Merge pull request #2527 from andysim/nhcommon

Convert Nose Hoover integrator to Common plaform

openmmapi/include/openmm/NoseHooverIntegrator.h

@@ -264,6 +264,10 @@ protected:
      * Compute the kinetic energy of the system at the current time.
      */
     virtual double computeKineticEnergy();
+    /**
+     * Computing kinetic energy for this integrator does not require forces.
+     */
+    bool kineticEnergyRequiresForce() const override;
 
     std::vector<NoseHooverChain> noseHooverChains;
     std::vector<int> allAtoms;

openmmapi/src/NoseHooverIntegrator.cpp

@@ -267,6 +267,7 @@ void NoseHooverIntegrator::setRelativeCollisionFrequency(double frequency, int c
 }
 
 double NoseHooverIntegrator::computeKineticEnergy() {
+    forcesAreValid = false;
     double kE = 0.0;
     if(noseHooverChains.size() > 0) {
         for (const auto &nhc: noseHooverChains){
@@ -278,6 +279,10 @@ double NoseHooverIntegrator::computeKineticEnergy() {
     return kE;
 }
 
+bool NoseHooverIntegrator::kineticEnergyRequiresForce() const {
+    return false;
+}
+
 double NoseHooverIntegrator::computeHeatBathEnergy() {
     double energy = 0;
     for(auto &nhc : noseHooverChains) {
@@ -340,7 +345,8 @@ void NoseHooverIntegrator::step(int steps) {
         throw OpenMMException("This Integrator is not bound to a context!");
     std::pair<double, double> scale, kineticEnergy;
     for (int i = 0; i < steps; ++i) {
-        context->updateContextState();
+        if(context->updateContextState())
+            forcesAreValid = false;
         for(auto &nhc : noseHooverChains) {
             kineticEnergy = nhcKernel.getAs<NoseHooverChainKernel>().computeMaskedKineticEnergy(*context, nhc, false);
             scale = nhcKernel.getAs<NoseHooverChainKernel>().propagateChain(*context, nhc, kineticEnergy, getStepSize());

platforms/common/include/openmm/common/CommonKernels.h

@@ -941,6 +941,116 @@ private:
     ComputeKernel kernel1, kernel2, kernel3;
 };
 
+/*
+ * This kernel is invoked by NoseHooverIntegrator to take one time step.
+ */
+class CommonIntegrateVelocityVerletStepKernel : public IntegrateVelocityVerletStepKernel {
+public:
+    CommonIntegrateVelocityVerletStepKernel(std::string name, const Platform& platform, ComputeContext& cc) :
+                                  IntegrateVelocityVerletStepKernel(name, platform), cc(cc), hasInitializedKernels(false) { }
+    ~CommonIntegrateVelocityVerletStepKernel() {}
+    /**
+     * Initialize the kernel.
+     *
+     * @param system     the System this kernel will be applied to
+     * @param integrator the NoseHooverIntegrator this kernel will be used for
+     */
+    void initialize(const System& system, const NoseHooverIntegrator& integrator);
+    /**
+     * Execute the kernel.
+     *
+     * @param context    the context in which to execute this kernel
+     * @param integrator the VerletIntegrator this kernel is being used for
+     * @param forcesAreValid a reference to the parent integrator's boolean for keeping
+     *                       track of the validity of the current forces.
+     */
+    void execute(ContextImpl& context, const NoseHooverIntegrator& integrator, bool &forcesAreValid);
+    /**
+     * Compute the kinetic energy.
+     *
+     * @param context    the context in which to execute this kernel
+     * @param integrator the NoseHooverIntegrator this kernel is being used for
+     */
+    double computeKineticEnergy(ContextImpl& context, const NoseHooverIntegrator& integrator);
+private:
+    ComputeContext& cc;
+    float prevMaxPairDistance;
+    ComputeArray maxPairDistanceBuffer, pairListBuffer, atomListBuffer, pairTemperatureBuffer;
+    ComputeKernel kernel1, kernel2, kernel3, kernelHardWall;
+    bool hasInitializedKernels;
+};
+
+/**
+ * This kernel is invoked by NoseHooverChain at the start of each time step to adjust the thermostat
+ * and update the associated particle velocities.
+ */
+class CommonNoseHooverChainKernel : public NoseHooverChainKernel {
+public:
+    CommonNoseHooverChainKernel(std::string name, const Platform& platform, ComputeContext& cc) :
+                 NoseHooverChainKernel(name, platform), cc(cc), hasInitializedPropagateKernel(false),
+                 hasInitializedKineticEnergyKernel(false), hasInitializedHeatBathEnergyKernel(false),
+                 hasInitializedScaleVelocitiesKernel(false) {}
+    ~CommonNoseHooverChainKernel() {}
+    /**
+     * Initialize the kernel.
+     */
+    void initialize();
+    /**
+     * Execute the kernel that propagates the Nose Hoover chain and determines the velocity scale factor.
+     *
+     * @param context  the context in which to execute this kernel
+     * @param noseHooverChain the object describing the chain to be propagated.
+     * @param kineticEnergies the {absolute, relative} kineticEnergy of the particles being thermostated by this chain.
+     * @param timeStep the time step used by the integrator.
+     * @return the {absolute, relative} velocity scale factor to apply to the particles associated with this heat bath.
+     */
+    std::pair<double, double> propagateChain(ContextImpl& context, const NoseHooverChain &nhc, std::pair<double, double> kineticEnergies, double timeStep);
+    /**
+     * Execute the kernal that computes the total (kinetic + potential) heat bath energy.
+     *
+     * @param context the context in which to execute this kernel
+     * @param noseHooverChain the chain whose energy is to be determined.
+     * @return the total heat bath energy.
+     */
+    double computeHeatBathEnergy(ContextImpl& context, const NoseHooverChain &nhc);
+    /**
+     * Execute the kernel that computes the kinetic energy for a subset of atoms,
+     * or the relative kinetic energy of Drude particles with respect to their parent atoms
+     *
+     * @param context the context in which to execute this kernel
+     * @param noseHooverChain the chain whose energy is to be determined.
+     * @param downloadValue whether the computed value should be downloaded and returned.
+     *
+     */
+    std::pair<double,double> computeMaskedKineticEnergy(ContextImpl& context, const NoseHooverChain &noseHooverChain, bool downloadValue);
+
+    /**
+     * Execute the kernel that scales the velocities of particles associated with a nose hoover chain
+     *
+     * @param context the context in which to execute this kernel
+     * @param noseHooverChain the chain whose energy is to be determined.
+     * @param scaleFactors the {absolute, relative} multiplicative factor by which velocities are scaled.
+     */
+    void scaleVelocities(ContextImpl& context, const NoseHooverChain &noseHooverChain, std::pair<double, double> scaleFactors);
+
+private:
+    int sumWorkGroupSize;
+    ComputeContext& cc;
+    ComputeArray energyBuffer, scaleFactorBuffer, kineticEnergyBuffer, chainMasses, chainForces, heatBathEnergy;
+    std::map<int, ComputeArray> atomlists, pairlists;
+    std::map<int, ComputeKernel> propagateKernels;
+    bool hasInitializedPropagateKernel;
+    bool hasInitializedKineticEnergyKernel;
+    bool hasInitializedHeatBathEnergyKernel;
+    bool hasInitializedScaleVelocitiesKernel;
+    ComputeKernel reduceEnergyKernel;
+    ComputeKernel computeHeatBathEnergyKernel;
+    ComputeKernel computeAtomsKineticEnergyKernel;
+    ComputeKernel computePairsKineticEnergyKernel;
+    ComputeKernel scaleAtomsVelocitiesKernel;
+    ComputeKernel scalePairsVelocitiesKernel;
+};
+
 /**
  * This kernel is invoked by BrownianIntegrator to take one time step.
  */

platforms/common/src/CommonKernels.cpp

@@ -5640,6 +5640,550 @@ double CommonIntegrateLangevinMiddleStepKernel::computeKineticEnergy(ContextImpl
     return cc.getIntegrationUtilities().computeKineticEnergy(0.0);
 }
 
+void CommonIntegrateVelocityVerletStepKernel::initialize(const System& system, const NoseHooverIntegrator& integrator) {
+    cc.initializeContexts();
+    map<string, string> defines;
+    defines["BOLTZ"] = cc.doubleToString(BOLTZ);
+    ComputeProgram program = cc.compileProgram(CommonKernelSources::velocityVerlet, defines);
+    kernel1 = program->createKernel("integrateVelocityVerletPart1");
+    kernel2 = program->createKernel("integrateVelocityVerletPart2");
+    kernel3 = program->createKernel("integrateVelocityVerletPart3");
+    kernelHardWall = program->createKernel("integrateVelocityVerletHardWall");
+    prevMaxPairDistance = -1.0f;
+    maxPairDistanceBuffer.initialize<float>(cc, 1, "maxPairDistanceBuffer");
+}
+
+void CommonIntegrateVelocityVerletStepKernel::execute(ContextImpl& context, const NoseHooverIntegrator& integrator, bool &forcesAreValid) {
+    IntegrationUtilities& integration = cc.getIntegrationUtilities();
+    int paddedNumAtoms = cc.getPaddedNumAtoms();
+    double dt = integrator.getStepSize();
+    cc.getIntegrationUtilities().setNextStepSize(dt);
+
+    // If the atom reordering has occured, the forces from the previous step are permuted and thus invalid.
+    // They need to be either sorted or recomputed; here we choose the latter.
+    if (!forcesAreValid || cc.getAtomsWereReordered()) context.calcForcesAndEnergy(true, false);
+
+    const auto& atomList = integrator.getAllThermostatedIndividualParticles();
+    const auto& pairList = integrator.getAllThermostatedPairs();
+    int numAtoms = atomList.size();
+    int numPairs = pairList.size();
+    int numParticles = numAtoms + 2*numPairs;
+    float maxPairDistance = integrator.getMaximumPairDistance();
+    // Make sure atom and pair metadata is uploaded and has the correct dimensions
+    if (prevMaxPairDistance != maxPairDistance) {
+        std::vector<float> tmp(1, maxPairDistance);
+        maxPairDistanceBuffer.upload(tmp);
+        prevMaxPairDistance = maxPairDistance;
+    }
+    if (numAtoms !=0 && (!atomListBuffer.isInitialized() || atomListBuffer.getSize() != numAtoms)) {
+        if (atomListBuffer.isInitialized())
+            atomListBuffer.resize(atomList.size());
+        else
+            atomListBuffer.initialize<int>(cc, atomList.size(), "atomListBuffer");
+        atomListBuffer.upload(atomList);
+    }
+    if (numPairs !=0 && (!pairListBuffer.isInitialized() || pairListBuffer.getSize() != numPairs)) {
+        if (pairListBuffer.isInitialized()) {
+            pairListBuffer.resize(pairList.size());
+            pairTemperatureBuffer.resize(pairList.size());
+        }
+        else {
+            pairListBuffer.initialize<mm_int2>(cc, pairList.size(), "pairListBuffer");
+            pairTemperatureBuffer.initialize<float>(cc, pairList.size(), "pairTemperatureBuffer");
+        }
+        std::vector<mm_int2> tmp;
+        std::vector<float> tmp2;
+        for(const auto &pair : pairList) {
+            tmp.push_back(mm_int2(std::get<0>(pair), std::get<1>(pair)));
+            tmp2.push_back(std::get<2>(pair));
+        }
+        pairListBuffer.upload(tmp);
+        pairTemperatureBuffer.upload(tmp2);
+    }
+
+    if (!hasInitializedKernels) {
+        hasInitializedKernels = true;
+        kernel1->addArg(numAtoms);
+        kernel1->addArg(numPairs);
+        kernel1->addArg(paddedNumAtoms);
+        kernel1->addArg(cc.getIntegrationUtilities().getStepSize());
+        kernel1->addArg(cc.getPosq());
+        kernel1->addArg(cc.getVelm());
+        kernel1->addArg(cc.getLongForceBuffer());
+        kernel1->addArg(integration.getPosDelta());
+        kernel1->addArg(numAtoms > 0 ? atomListBuffer : cc.getEnergyBuffer()); // The array is not used if num == 0
+        kernel1->addArg(numPairs > 0 ? pairListBuffer : cc.getEnergyBuffer()); // The array is not used if num == 0
+        if (cc.getUseMixedPrecision())
+            kernel1->addArg(cc.getPosqCorrection());
+        kernel2->addArg(numParticles);
+        kernel2->addArg(cc.getIntegrationUtilities().getStepSize());
+        kernel2->addArg(cc.getPosq());
+        kernel2->addArg(cc.getVelm());
+        kernel2->addArg(integration.getPosDelta());
+        if (cc.getUseMixedPrecision())
+            kernel2->addArg(cc.getPosqCorrection());
+        if (numPairs > 0) {
+            kernelHardWall->addArg(numPairs);
+            kernelHardWall->addArg(maxPairDistanceBuffer);
+            kernelHardWall->addArg(cc.getIntegrationUtilities().getStepSize());
+            kernelHardWall->addArg(cc.getPosq());
+            kernelHardWall->addArg(cc.getVelm());
+            kernelHardWall->addArg(pairListBuffer);
+            kernelHardWall->addArg(pairTemperatureBuffer);
+            if (cc.getUseMixedPrecision())
+                kernelHardWall->addArg(cc.getPosqCorrection());
+        }
+        kernel3->addArg(numAtoms);
+        kernel3->addArg(numPairs);
+        kernel3->addArg(paddedNumAtoms);
+        kernel3->addArg(cc.getIntegrationUtilities().getStepSize());
+        kernel3->addArg(cc.getPosq());
+        kernel3->addArg(cc.getVelm());
+        kernel3->addArg(cc.getLongForceBuffer());
+        kernel3->addArg(integration.getPosDelta());
+        kernel3->addArg(numAtoms > 0 ? atomListBuffer : cc.getEnergyBuffer()); // The array is not used if num == 0
+        kernel3->addArg(numPairs > 0 ? pairListBuffer : cc.getEnergyBuffer()); // The array is not used if num == 0
+        if (cc.getUseMixedPrecision())
+            kernel3->addArg(cc.getPosqCorrection());
+    }
+
+    /*
+     * Carry out the integration
+     */
+
+    // Advance the velocities a half step
+    kernel1->execute(std::max(numAtoms, numPairs));
+    integration.applyConstraints(integrator.getConstraintTolerance());
+    // Advance particle positions a full step
+    kernel2->execute(numParticles);
+    // Make sure any Drude-like particles have not wandered too far from home
+    if (numPairs > 0) kernelHardWall->execute(numPairs);
+    integration.computeVirtualSites();
+    context.calcForcesAndEnergy(true, false);
+    forcesAreValid = true;
+    // Update velocities another half step
+    kernel3->execute(std::max(numAtoms, numPairs));
+    integration.applyVelocityConstraints(integrator.getConstraintTolerance());
+
+    cc.setTime(cc.getTime()+dt);
+    cc.setStepCount(cc.getStepCount()+1);
+    cc.reorderAtoms();
+}
+
+double CommonIntegrateVelocityVerletStepKernel::computeKineticEnergy(ContextImpl& context, const NoseHooverIntegrator& integrator) {
+    return cc.getIntegrationUtilities().computeKineticEnergy(0);
+}
+
+void CommonNoseHooverChainKernel::initialize() {
+    bool useDouble = cc.getUseDoublePrecision() || cc.getUseMixedPrecision();
+    map<string, string> defines;
+    int workGroupSize = std::min(cc.getMaxThreadBlockSize(), 512);
+    defines["WORK_GROUP_SIZE"] = std::to_string(workGroupSize);
+    defines["BEGIN_YS_LOOP"] = "const real arr[1] = {1.0}; for(int i=0;i<1;++i) { const real ys = arr[i];";
+    defines["END_YS_LOOP"] = "}";
+    ComputeProgram program = cc.compileProgram(CommonKernelSources::noseHooverChain, defines);
+    propagateKernels[1] = program->createKernel("propagateNoseHooverChain");
+    defines["BEGIN_YS_LOOP"] = "const real arr[3] = {0.828981543588751, -0.657963087177502, 0.828981543588751}; for(int i=0;i<3;++i) { const real ys = arr[i];";
+    program = cc.compileProgram(CommonKernelSources::noseHooverChain, defines);
+    propagateKernels[3] = program->createKernel("propagateNoseHooverChain");
+    defines["BEGIN_YS_LOOP"] = "const real arr[5] = {0.2967324292201065, 0.2967324292201065, -0.186929716880426, 0.2967324292201065, 0.2967324292201065}; for(int i=0;i<5;++i) { const real ys = arr[i];";
+    program = cc.compileProgram(CommonKernelSources::noseHooverChain, defines);
+    propagateKernels[5] = program->createKernel("propagateNoseHooverChain");
+    program = cc.compileProgram(CommonKernelSources::noseHooverChain, defines);
+    reduceEnergyKernel = program->createKernel("reduceEnergyPair");
+
+    computeHeatBathEnergyKernel = program->createKernel("computeHeatBathEnergy");
+    computeAtomsKineticEnergyKernel = program->createKernel("computeAtomsKineticEnergy");
+    computePairsKineticEnergyKernel = program->createKernel("computePairsKineticEnergy");
+    scaleAtomsVelocitiesKernel = program->createKernel("scaleAtomsVelocities");
+    scalePairsVelocitiesKernel = program->createKernel("scalePairsVelocities");
+    int energyBufferSize = cc.getEnergyBuffer().getSize();
+    if (cc.getUseDoublePrecision() || cc.getUseMixedPrecision())
+        energyBuffer.initialize<mm_double2>(cc, energyBufferSize, "energyBuffer");
+    else
+        energyBuffer.initialize<mm_float2>(cc, energyBufferSize, "energyBuffer");
+}
+
+std::pair<double, double> CommonNoseHooverChainKernel::propagateChain(ContextImpl& context, const NoseHooverChain &nhc, std::pair<double, double> kineticEnergies, double timeStep) {
+    bool useDouble = cc.getUseDoublePrecision() || cc.getUseMixedPrecision();
+    int chainID = nhc.getChainID();
+    int nAtoms = nhc.getThermostatedAtoms().size();
+    int nPairs = nhc.getThermostatedPairs().size();
+    int chainLength = nhc.getChainLength();
+    int numYS = nhc.getNumYoshidaSuzukiTimeSteps();
+    int numMTS = nhc.getNumMultiTimeSteps();
+
+    if (numYS != 1 && numYS != 3 && numYS != 5) {
+        throw OpenMMException("Number of Yoshida Suzuki time steps has to be 1, 3, or 5.");
+    }
+
+    auto & chainState = cc.getIntegrationUtilities().getNoseHooverChainState();
+
+    if (!scaleFactorBuffer.isInitialized() || scaleFactorBuffer.getSize() == 0) {
+        if (useDouble) {
+            std::vector<mm_double2> zeros{{0,0}};
+            if (scaleFactorBuffer.isInitialized())
+                scaleFactorBuffer.resize(1);
+            else
+                scaleFactorBuffer.initialize<mm_double2>(cc, 1, "scaleFactorBuffer");
+            scaleFactorBuffer.upload(zeros);
+        }
+        else {
+            std::vector<mm_float2> zeros{{0,0}};
+            if (scaleFactorBuffer.isInitialized())
+                scaleFactorBuffer.resize(1);
+            else
+                scaleFactorBuffer.initialize<mm_float2>(cc, 1, "scaleFactorBuffer");
+            scaleFactorBuffer.upload(zeros);
+        }
+    }
+    if (!chainForces.isInitialized() || !chainMasses.isInitialized()) {
+        if (useDouble) {
+            std::vector<double> zeros(chainLength,0);
+            if (chainForces.isInitialized()) {
+                chainMasses.resize(chainLength);
+                chainForces.resize(chainLength);
+            }
+            else {
+                chainMasses.initialize<double>(cc, chainLength, "chainMasses");
+                chainForces.initialize<double>(cc, chainLength, "chainForces");
+            }
+            chainMasses.upload(zeros);
+            chainForces.upload(zeros);
+        }
+        else {
+            std::vector<float> zeros(chainLength,0);
+            if (chainForces.isInitialized()) {
+                chainMasses.resize(chainLength);
+                chainForces.resize(chainLength);
+            }
+            else {
+                chainMasses.initialize<float>(cc, chainLength, "chainMasses");
+                chainForces.initialize<float>(cc, chainLength, "chainForces");
+            }
+            chainMasses.upload(zeros);
+            chainForces.upload(zeros);
+        }
+    }
+    if (chainForces.getSize() < chainLength)
+        chainForces.resize(chainLength);
+    if (chainMasses.getSize() < chainLength)
+        chainMasses.resize(chainLength);
+
+
+    // N.B. We ignore the incoming kineticEnergy and grab it from the device buffer instead
+    if (nAtoms) {
+        if (!chainState.count(2*chainID))
+            chainState[2*chainID] = ComputeArray();
+        if (!chainState.at(2*chainID).isInitialized() || chainState.at(2*chainID).getSize() != chainLength) {
+            // We need to upload the Common array
+            if (useDouble) {
+                if (chainState.at(2*chainID).isInitialized())
+                    chainState.at(2*chainID).resize(chainLength);
+                else
+                    chainState.at(2*chainID).initialize<mm_double2>(cc, chainLength, "chainState" + std::to_string(2*chainID));
+                std::vector<mm_double2> zeros(chainLength, mm_double2(0.0, 0.0));
+                chainState.at(2*chainID).upload(zeros.data());
+            }
+            else {
+                if (chainState.at(2*chainID).isInitialized())
+                    chainState.at(2*chainID).resize(chainLength);
+                else
+                    chainState.at(2*chainID).initialize<mm_float2>(cc, chainLength, "chainState" + std::to_string(2*chainID));
+                std::vector<mm_float2> zeros(chainLength, mm_float2(0.0f, 0.0f));
+                chainState.at(2*chainID).upload(zeros.data());
+            }
+        }
+    }
+
+    if (nPairs) {
+        if (!chainState.count(2*chainID+1))
+            chainState[2*chainID+1] = ComputeArray();
+        if (!chainState.at(2*chainID+1).isInitialized() || chainState.at(2*chainID+1).getSize() != chainLength) {
+            // We need to upload the Common array
+            if (useDouble) {
+                if (chainState.at(2*chainID+1).isInitialized())
+                    chainState.at(2*chainID+1).resize(chainLength);
+                else
+                    chainState.at(2*chainID+1).initialize<mm_double2>(cc, chainLength, "chainState" + std::to_string(2*chainID+1));
+                std::vector<mm_double2> zeros(chainLength, mm_double2(0.0, 0.0));
+                chainState.at(2*chainID+1).upload(zeros.data());
+            }
+            else {
+                if (chainState.at(2*chainID+1).isInitialized())
+                    chainState.at(2*chainID+1).resize(chainLength);
+                else
+                    chainState.at(2*chainID+1).initialize<mm_float2>(cc, chainLength, "chainState" + std::to_string(2*chainID+1));
+                std::vector<mm_float2> zeros(chainLength, mm_float2(0.0f, 0.0f));
+                chainState.at(2*chainID+1).upload(zeros.data());
+            }
+        }
+    }
+
+    if (!hasInitializedPropagateKernel) {
+        hasInitializedPropagateKernel = true;
+        propagateKernels[numYS]->addArg(); // ChainState
+        propagateKernels[numYS]->addArg(kineticEnergyBuffer);
+        propagateKernels[numYS]->addArg(scaleFactorBuffer);
+        propagateKernels[numYS]->addArg(chainMasses);
+        propagateKernels[numYS]->addArg(chainForces);
+        propagateKernels[numYS]->addArg(); // ChainType
+        propagateKernels[numYS]->addArg(chainLength);
+        propagateKernels[numYS]->addArg(numMTS);
+        propagateKernels[numYS]->addArg(); // numDoFs
+        propagateKernels[numYS]->addArg((float)timeStep);
+        propagateKernels[numYS]->addArg(); // kT
+        propagateKernels[numYS]->addArg(); // frequency
+    }
+
+    if (nAtoms) {
+        int chainType = 0;
+        double temperature = nhc.getTemperature();
+        float frequency = nhc.getCollisionFrequency();
+        double kT = BOLTZ * temperature;
+        int numDOFs = nhc.getNumDegreesOfFreedom();
+        propagateKernels[numYS]->setArg(0, chainState[2*chainID]);
+        propagateKernels[numYS]->setArg(5, chainType);
+        propagateKernels[numYS]->setArg(8, numDOFs);
+        if (useDouble) {
+            propagateKernels[numYS]->setArg(10, kT);
+        } else {
+            propagateKernels[numYS]->setArg(10, (float)kT);
+        }
+        propagateKernels[numYS]->setArg(11, frequency);
+        propagateKernels[numYS]->execute(1, 1);
+    }
+    if (nPairs) {
+        int chainType = 1;
+        double relativeTemperature = nhc.getRelativeTemperature();
+        float relativeFrequency = nhc.getRelativeCollisionFrequency();
+        double kT = BOLTZ * relativeTemperature;
+        int ndf = 3*nPairs;
+        propagateKernels[numYS]->setArg(0, chainState[2*chainID+1]);
+        propagateKernels[numYS]->setArg(5, chainType);
+        propagateKernels[numYS]->setArg(8, ndf);
+        if (useDouble) {
+            propagateKernels[numYS]->setArg(10, kT);
+        } else {
+            propagateKernels[numYS]->setArg(10, (float)kT);
+        }
+        propagateKernels[numYS]->setArg(11, relativeFrequency);
+        propagateKernels[numYS]->execute(1, 1);
+    }
+    return {0, 0};
+}
+
+double CommonNoseHooverChainKernel::computeHeatBathEnergy(ContextImpl& context, const NoseHooverChain &nhc) {
+
+    bool useDouble = cc.getUseDoublePrecision() || cc.getUseMixedPrecision();
+
+    int chainID = nhc.getChainID();
+    int chainLength = nhc.getChainLength();
+
+    auto & chainState = cc.getIntegrationUtilities().getNoseHooverChainState();
+
+    bool absChainIsValid = chainState.count(2*chainID) != 0 &&
+                           chainState[2*chainID].isInitialized() &&
+                           chainState[2*chainID].getSize() == chainLength;
+    bool relChainIsValid = chainState.count(2*chainID+1) != 0 &&
+                           chainState[2*chainID+1].isInitialized() &&
+                           chainState[2*chainID+1].getSize() == chainLength;
+
+    if (!absChainIsValid && !relChainIsValid) return 0.0;
+
+    if (!heatBathEnergy.isInitialized() || heatBathEnergy.getSize() == 0) {
+        if (useDouble) {
+            std::vector<double> one(1);
+            heatBathEnergy.initialize<double>(cc, 1, "heatBathEnergy");
+            heatBathEnergy.upload(one);
+        }
+        else {
+            std::vector<float> one(1);
+            heatBathEnergy.initialize<float>(cc, 1, "heatBathEnergy");
+            heatBathEnergy.upload(one);
+        }
+    }
+
+    cc.clearBuffer(heatBathEnergy);
+
+    if(!hasInitializedHeatBathEnergyKernel) {
+        hasInitializedHeatBathEnergyKernel = true;
+        computeHeatBathEnergyKernel->addArg(heatBathEnergy);
+        computeHeatBathEnergyKernel->addArg(chainLength);
+        computeHeatBathEnergyKernel->addArg(); // numDOFs
+        computeHeatBathEnergyKernel->addArg(); // kT
+        computeHeatBathEnergyKernel->addArg(); // frequency
+        computeHeatBathEnergyKernel->addArg(); // chainstate
+    }
+
+    if (absChainIsValid) {
+        int numDOFs = nhc.getNumDegreesOfFreedom();
+        double temperature = nhc.getTemperature();
+        float frequency = nhc.getCollisionFrequency();
+        double kT = BOLTZ * temperature;
+
+        computeHeatBathEnergyKernel->setArg(2, numDOFs);
+        if (useDouble) {
+            computeHeatBathEnergyKernel->setArg(3, kT);
+        } else {
+            computeHeatBathEnergyKernel->setArg(3, (float)kT);
+        }
+        computeHeatBathEnergyKernel->setArg(4, frequency);
+        computeHeatBathEnergyKernel->setArg(5, chainState[2*chainID]);
+        computeHeatBathEnergyKernel->execute(1, 1);
+    }
+    if (relChainIsValid) {
+        int numDOFs = 3 * nhc.getThermostatedPairs().size();
+        double temperature = nhc.getRelativeTemperature();
+        float frequency = nhc.getRelativeCollisionFrequency();
+        double kT = BOLTZ * temperature;
+
+        computeHeatBathEnergyKernel->setArg(2, numDOFs);
+        if (useDouble) {
+            computeHeatBathEnergyKernel->setArg(3, kT);
+        } else {
+            computeHeatBathEnergyKernel->setArg(3, (float)kT);
+        }
+        computeHeatBathEnergyKernel->setArg(4, frequency);
+        computeHeatBathEnergyKernel->setArg(5, chainState[2*chainID+1]);
+        computeHeatBathEnergyKernel->execute(1, 1);
+    }
+
+
+    void * pinnedBuffer = cc.getPinnedBuffer();
+    heatBathEnergy.download(pinnedBuffer);
+    if (useDouble)
+        return *((double*) pinnedBuffer);
+    else
+        return *((float*) pinnedBuffer);
+}
+
+std::pair<double, double> CommonNoseHooverChainKernel::computeMaskedKineticEnergy(ContextImpl& context, const NoseHooverChain &nhc, bool downloadValue) {
+
+    bool useDouble = cc.getUseDoublePrecision() || cc.getUseMixedPrecision();
+
+    int chainID = nhc.getChainID();
+    const auto & nhcAtoms = nhc.getThermostatedAtoms();
+    const auto & nhcPairs = nhc.getThermostatedPairs();
+    int nAtoms = nhcAtoms.size();
+    int nPairs = nhcPairs.size();
+    if (nAtoms) {
+        if (!atomlists.count(chainID)) {
+            // We need to upload the Common array
+            atomlists[chainID] = ComputeArray();
+            atomlists[chainID].initialize<int>(cc, nAtoms, "atomlist" + std::to_string(chainID));
+            atomlists[chainID].upload(nhcAtoms);
+        }
+        if (atomlists[chainID].getSize() != nAtoms) {
+            throw OpenMMException("Number of atoms changed. Cannot be handled by the same Nose-Hoover thermostat.");
+        }
+    }
+    if (nPairs) {
+        if (!pairlists.count(chainID)) {
+            // We need to upload the Common array
+            pairlists[chainID] = ComputeArray();
+            pairlists[chainID].initialize<mm_int2>(cc, nPairs, "pairlist" + std::to_string(chainID));
+            std::vector<mm_int2> int2vec;
+            for(const auto &p : nhcPairs) int2vec.push_back(mm_int2(p.first, p.second));
+            pairlists[chainID].upload(int2vec);
+        }
+        if (pairlists[chainID].getSize() != nPairs) {
+            throw OpenMMException("Number of thermostated pairs changed. Cannot be handled by the same Nose-Hoover thermostat.");
+        }
+    }
+    if (!kineticEnergyBuffer.isInitialized() || kineticEnergyBuffer.getSize() == 0) {
+        if (useDouble) {
+            std::vector<mm_double2> zeros{{0,0}};
+            kineticEnergyBuffer.initialize<mm_double2>(cc, 1, "kineticEnergyBuffer");
+            kineticEnergyBuffer.upload(zeros);
+        }
+        else {
+            std::vector<mm_float2> zeros{{0,0}};
+            kineticEnergyBuffer.initialize<mm_float2>(cc, 1, "kineticEnergyBuffer");
+            kineticEnergyBuffer.upload(zeros);
+        }
+    }
+
+    int workGroupSize = std::min(cc.getMaxThreadBlockSize(), 512);
+    if (!hasInitializedKineticEnergyKernel) {
+        hasInitializedKineticEnergyKernel = true;
+        computeAtomsKineticEnergyKernel->addArg(energyBuffer);
+        computeAtomsKineticEnergyKernel->addArg(); // nAtoms
+        computeAtomsKineticEnergyKernel->addArg(cc.getVelm());
+        computeAtomsKineticEnergyKernel->addArg(); // atom list
+
+        computePairsKineticEnergyKernel->addArg(energyBuffer);
+        computePairsKineticEnergyKernel->addArg(); // nPairs
+        computePairsKineticEnergyKernel->addArg(cc.getVelm());
+        computePairsKineticEnergyKernel->addArg(); // pair list
+
+        reduceEnergyKernel->addArg(energyBuffer);
+        reduceEnergyKernel->addArg(kineticEnergyBuffer);
+        reduceEnergyKernel->addArg(energyBuffer.getSize());
+    }
+
+    cc.clearBuffer(energyBuffer);
+    if (nAtoms) {
+        computeAtomsKineticEnergyKernel->setArg(1, nAtoms);
+        computeAtomsKineticEnergyKernel->setArg(3, atomlists[chainID]);
+        computeAtomsKineticEnergyKernel->execute(nAtoms);
+    }
+    if (nPairs) {
+        computePairsKineticEnergyKernel->setArg(1, nPairs);
+        computePairsKineticEnergyKernel->setArg(3, pairlists[chainID]);
+        computePairsKineticEnergyKernel->execute(nPairs);
+    }
+    reduceEnergyKernel->execute(workGroupSize, workGroupSize);
+
+    std::pair<double, double> KEs = {0, 0};
+    if (downloadValue) {
+        if (useDouble) {
+            mm_double2 tmp;
+            kineticEnergyBuffer.download(&tmp);
+            KEs.first = tmp.x;
+            KEs.second = tmp.y;
+        }
+        else {
+            mm_float2 tmp;
+            kineticEnergyBuffer.download(&tmp);
+            KEs.first = tmp.x;
+            KEs.second = tmp.y;
+        }
+    }
+    return KEs;
+}
+
+void CommonNoseHooverChainKernel::scaleVelocities(ContextImpl& context, const NoseHooverChain &nhc, std::pair<double, double> scaleFactor) {
+    // For now we assume that the atoms and pairs info is valid, because compute{Atoms|Pairs}KineticEnergy must have been
+    // called before this kernel.  If that ever ceases to be true, some sanity checks are needed here.
+
+    int chainID = nhc.getChainID();
+    int nAtoms = nhc.getThermostatedAtoms().size();
+    int nPairs = nhc.getThermostatedPairs().size();
+    if (!hasInitializedScaleVelocitiesKernel) {
+        hasInitializedScaleVelocitiesKernel = true;
+        scaleAtomsVelocitiesKernel->addArg(scaleFactorBuffer);
+        scaleAtomsVelocitiesKernel->addArg(); // nAtoms
+        scaleAtomsVelocitiesKernel->addArg(cc.getVelm());
+        scaleAtomsVelocitiesKernel->addArg(); // atom list
+
+        scalePairsVelocitiesKernel->addArg(scaleFactorBuffer);
+        scalePairsVelocitiesKernel->addArg(); // nPairs
+        scalePairsVelocitiesKernel->addArg(cc.getVelm());
+        scalePairsVelocitiesKernel->addArg(); // pair list
+    }
+    if (nAtoms) {
+        scaleAtomsVelocitiesKernel->setArg(1, nAtoms);
+        scaleAtomsVelocitiesKernel->setArg(3, atomlists[chainID]);
+        scaleAtomsVelocitiesKernel->execute(nAtoms);
+    }
+    if (nPairs) {
+        scalePairsVelocitiesKernel->setArg(1, nPairs);
+        scalePairsVelocitiesKernel->setArg(3, pairlists[chainID]);
+        scalePairsVelocitiesKernel->execute(nPairs);
+    }
+}
+
 void CommonIntegrateBrownianStepKernel::initialize(const System& system, const BrownianIntegrator& integrator) {
     cc.initializeContexts();
     cc.setAsCurrent();

platforms/opencl/src/kernels/noseHooverChain.cl → platforms/common/src/kernels/noseHooverChain.cc

-
-//#include <initializer_list>
-
-__kernel void propagateNoseHooverChain(__global mixed2* restrict chainData, __global const mixed2 * restrict energySum, __global mixed2* restrict scaleFactor,
-                                                    __global mixed* restrict chainMasses, __global mixed* restrict chainForces, 
-                                                    int chainType, int chainLength, int numMTS, int numDOFs, float timeStep,
-                                                    mixed kT, float frequency){
+KERNEL void propagateNoseHooverChain(GLOBAL mixed2* RESTRICT chainData, GLOBAL const mixed2 * RESTRICT energySum, GLOBAL mixed2* RESTRICT scaleFactor,
+                                     GLOBAL mixed* RESTRICT chainMasses, GLOBAL mixed* RESTRICT chainForces, int chainType, int chainLength, int numMTS,
+                                     int numDOFs, float timeStep, mixed kT, float frequency){
     const mixed kineticEnergy = chainType == 0 ? energySum[0].x : energySum[0].y;
     mixed scale = 1;
     if(kineticEnergy < 1e-8) return;
@@ -54,10 +50,9 @@ __kernel void propagateNoseHooverChain(__global mixed2* restrict chainData, __gl
 /**
  * Compute total (potential + kinetic) energy of the Nose-Hoover beads
  */
-__kernel void computeHeatBathEnergy(__global mixed* restrict heatBathEnergy, int chainLength, int numDOFs,
-                                                 mixed kT, float frequency, __global const mixed2* restrict chainData){
+KERNEL void computeHeatBathEnergy(GLOBAL mixed* RESTRICT heatBathEnergy, int chainLength, int numDOFs,
+                                  mixed kT, float frequency, GLOBAL const mixed2* RESTRICT chainData){
     // Note that this is always incremented; make sure it's zeroed properly before the first call
-
     for(int i = 0; i < chainLength; ++i) {
         mixed prefac = i ? 1 : numDOFs;
         mixed mass = prefac * kT / (frequency * frequency);
@@ -70,25 +65,24 @@ __kernel void computeHeatBathEnergy(__global mixed* restrict heatBathEnergy, int
     }
 }
 
-__kernel void computeAtomsKineticEnergy(__global mixed2 * restrict energyBuffer, int numAtoms,
-                                        __global const mixed4* restrict velm, __global const int *restrict atoms){
-    mixed2 energy = (mixed2) (0,0);
-    //energy = 1; return;
-    int index = get_global_id(0);
+KERNEL void computeAtomsKineticEnergy(GLOBAL mixed2 * RESTRICT energyBuffer, int numAtoms,
+                                      GLOBAL const mixed4* RESTRICT velm, GLOBAL const int *RESTRICT atoms){
+    mixed2 energy = make_mixed2(0,0);
+    int index = GLOBAL_ID;
     while (index < numAtoms){
         int atom = atoms[index];
         mixed4 v = velm[atom];
         mixed mass = v.w == 0 ? 0 : 1 / v.w;
         energy.x += 0.5f * mass * (v.x*v.x + v.y*v.y + v.z*v.z);
-        index += get_global_size(0);
+        index += GLOBAL_SIZE;
     }
-    energyBuffer[get_global_id(0)] = energy;
+    energyBuffer[GLOBAL_ID] = energy;
 }
 
-__kernel void computePairsKineticEnergy(__global mixed2 * restrict energyBuffer, int numPairs,
-                                        __global const mixed4* restrict velm, __global const int2 *restrict pairs){
-    mixed2 energy = (mixed2) (0,0);
-    int index = get_global_id(0);
+KERNEL void computePairsKineticEnergy(GLOBAL mixed2 * RESTRICT energyBuffer, int numPairs,
+                                      GLOBAL const mixed4* RESTRICT velm, GLOBAL const int2 *RESTRICT pairs){
+    mixed2 energy = make_mixed2(0,0);
+    int index = GLOBAL_ID;
     while (index < numPairs){
         int2 pair = pairs[index];
         int atom1 = pair.x;
@@ -107,64 +101,74 @@ __kernel void computePairsKineticEnergy(__global mixed2 * restrict energyBuffer,
         rv.z = v2.z - v1.z;
         energy.x += 0.5f * (m1 + m2) * (cv.x*cv.x + cv.y*cv.y + cv.z*cv.z);
         energy.y += 0.5f * (m1 * m2 / (m1 + m2)) * (rv.x*rv.x + rv.y*rv.y + rv.z*rv.z);
-        index += get_global_size(0);
+        index += GLOBAL_SIZE;
     }
     // The atoms version of this has been called already, so accumulate instead of assigning here
-    energyBuffer[get_global_id(0)].xy += energy.xy;
+    energyBuffer[GLOBAL_ID].x += energy.x;
+    energyBuffer[GLOBAL_ID].y += energy.y;
 }
 
-__kernel void scaleAtomsVelocities(__global mixed2* restrict scaleFactor, int numAtoms,
-                                   __global mixed4* restrict velm, __global const int *restrict atoms){
+KERNEL void scaleAtomsVelocities(GLOBAL mixed2* RESTRICT scaleFactor, int numAtoms,
+                                   GLOBAL mixed4* RESTRICT velm, GLOBAL const int *RESTRICT atoms){
     const mixed scale = scaleFactor[0].x;
-    int index = get_global_id(0);
+    int index = GLOBAL_ID;
     while (index < numAtoms){
         int atom = atoms[index];
         velm[atom].x *= scale;
         velm[atom].y *= scale;
         velm[atom].z *= scale;
-        index += get_global_size(0);
+        index += GLOBAL_SIZE;
     }
 }
 
-__kernel void scalePairsVelocities(__global mixed2 * restrict scaleFactor, int numPairs,
-                                   __global mixed4* restrict velm, __global const int2 *restrict pairs){
-    int index = get_global_id(0);
+KERNEL void scalePairsVelocities(GLOBAL mixed2 * RESTRICT scaleFactor, int numPairs,
+                                 GLOBAL mixed4* RESTRICT velm, GLOBAL const int2 *RESTRICT pairs){
+    int index = GLOBAL_ID;
+    mixed comScale = scaleFactor[0].x;
+    mixed relScale = scaleFactor[0].y;
     while (index < numPairs){
         int atom1 = pairs[index].x;
         int atom2 = pairs[index].y;
         mixed m1 = velm[atom1].w == 0 ? 0 : 1 / velm[atom1].w;
         mixed m2 = velm[atom2].w == 0 ? 0 : 1 / velm[atom2].w;
         mixed4 cv;
-        cv.xyz = (m1*velm[atom1].xyz + m2*velm[atom2].xyz) / (m1 + m2);
+        cv.x = (m1*velm[atom1].x + m2*velm[atom2].x) / (m1 + m2);
+        cv.y = (m1*velm[atom1].y + m2*velm[atom2].y) / (m1 + m2);
+        cv.z = (m1*velm[atom1].z + m2*velm[atom2].z) / (m1 + m2);
         mixed4 rv;
-        rv.xyz = velm[atom2].xyz - velm[atom1].xyz;
-        velm[atom1].x = scaleFactor[0].x * cv.x - scaleFactor[0].y * rv.x * m2 / (m1 + m2);
-        velm[atom1].y = scaleFactor[0].x * cv.y - scaleFactor[0].y * rv.y * m2 / (m1 + m2);
-        velm[atom1].z = scaleFactor[0].x * cv.z - scaleFactor[0].y * rv.z * m2 / (m1 + m2);
-        velm[atom2].x = scaleFactor[0].x * cv.x + scaleFactor[0].y * rv.x * m1 / (m1 + m2);
-        velm[atom2].y = scaleFactor[0].x * cv.y + scaleFactor[0].y * rv.y * m1 / (m1 + m2);
-        velm[atom2].z = scaleFactor[0].x * cv.z + scaleFactor[0].y * rv.z * m1 / (m1 + m2);
-        index += get_global_size(0);
+        rv.x = velm[atom2].x - velm[atom1].x;
+        rv.y = velm[atom2].y - velm[atom1].y;
+        rv.z = velm[atom2].z - velm[atom1].z;
+        velm[atom1].x = comScale * cv.x - relScale * rv.x * m2 / (m1 + m2);
+        velm[atom1].y = comScale * cv.y - relScale * rv.y * m2 / (m1 + m2);
+        velm[atom1].z = comScale * cv.z - relScale * rv.z * m2 / (m1 + m2);
+        velm[atom2].x = comScale * cv.x + relScale * rv.x * m1 / (m1 + m2);
+        velm[atom2].y = comScale * cv.y + relScale * rv.y * m1 / (m1 + m2);
+        velm[atom2].z = comScale * cv.z + relScale * rv.z * m1 / (m1 + m2);
+        index += GLOBAL_SIZE;
     }
 }
 
 /**
- * Sum the energy buffer containing a pair of energies stored as mixed2.  This is copied from utilities.cu with small modifications
+ * Sum the energy buffer containing a pair of energies stored as mixed2.  This is taken from the analogous customIntegrator code
  */
-__kernel void reduceEnergyPair(__global const mixed2* restrict energyBuffer, __global mixed2* restrict result, int bufferSize, int workGroupSize, __local mixed2* restrict tempBuffer) {
-    const unsigned int thread = get_local_id(0);
-    mixed2 sum = (mixed2) (0,0);
-    for (unsigned int index = thread; index < bufferSize; index += get_local_size(0)) {
-        sum.xy += energyBuffer[index].xy;
+KERNEL void reduceEnergyPair(GLOBAL const mixed2* RESTRICT sumBuffer, GLOBAL mixed2* result, int bufferSize) {
+    LOCAL mixed2 tempBuffer[WORK_GROUP_SIZE];
+    const unsigned int thread = LOCAL_ID;
+    mixed2 sum = make_mixed2(0,0);
+    for (unsigned int index = thread; index < bufferSize; index += LOCAL_SIZE) {
+        sum.x += sumBuffer[index].x;
+        sum.y += sumBuffer[index].y;
     }
-    tempBuffer[thread].xy = sum.xy;
-    for (int i = 1; i < workGroupSize; i *= 2) {
-        barrier(CLK_LOCAL_MEM_FENCE);
-        if (thread%(i*2) == 0 && thread+i < workGroupSize) {
-            tempBuffer[thread].xy += tempBuffer[thread+i].xy;
+    tempBuffer[thread].x = sum.x;
+    tempBuffer[thread].y = sum.y;
+    for (int i = 1; i < WORK_GROUP_SIZE; i *= 2) {
+        SYNC_THREADS;
+        if (thread%(i*2) == 0 && thread+i < WORK_GROUP_SIZE) {
+            tempBuffer[thread].x += tempBuffer[thread+i].x;
+            tempBuffer[thread].y += tempBuffer[thread+i].y;
         }
     }
-    if (thread == 0) {
+    if (thread == 0)
         *result = tempBuffer[0];
-    }
 }

platforms/cuda/src/kernels/velocityVerlet.cu → platforms/common/src/kernels/velocityVerlet.cc

 /**
  * Perform the first step of Velocity Verlet integration.
- * 
- * update displacements (posDelta) and velocities (velm)
  */
 
-extern "C" __global__ void integrateVelocityVerletPart1(int numAtoms, int numPairs, int paddedNumAtoms, const mixed2* __restrict__ dt, const real4* __restrict__ posq,
-        const real4* __restrict__ posqCorrection, mixed4* __restrict__ velm, const long long* __restrict__ force, mixed4* __restrict__ posDelta,
-        const int* __restrict__ atomList, const int2* __restrict__ pairList) {
+KERNEL void integrateVelocityVerletPart1(int numAtoms, int numPairs, int paddedNumAtoms, GLOBAL const mixed2* RESTRICT dt, GLOBAL const real4* RESTRICT posq,
+                                         GLOBAL mixed4* RESTRICT velm, GLOBAL const mm_long* RESTRICT force, GLOBAL mixed4* RESTRICT posDelta,
+                                         GLOBAL const int* RESTRICT atomList, GLOBAL const int2* RESTRICT pairList
+#ifdef USE_MIXED_PRECISION
+                                        ,GLOBAL const real4* RESTRICT posqCorrection
+#endif
+    ){
     const mixed2 stepSize = dt[0];
     const mixed dtPos = stepSize.y;
     const mixed dtVel = 0.5f*(stepSize.x+stepSize.y);
-    const mixed scale = 0.5f*dtVel/(mixed) 0x100000000;
-    for (int index = blockIdx.x*blockDim.x+threadIdx.x; index < numAtoms; index += blockDim.x*gridDim.x) {
+    const mixed scale = 0.5f * dtVel/(mixed) 0x100000000;
+    int index = GLOBAL_ID;
+    while (index < numAtoms) {
         int atom = atomList[index];
         mixed4 velocity = velm[atom];
         if (velocity.w != 0.0) {
@@ -31,8 +34,10 @@ extern "C" __global__ void integrateVelocityVerletPart1(int numAtoms, int numPai
             posDelta[atom] = pos;
             velm[atom] = velocity;
         }
+        index += GLOBAL_SIZE;
     }
-    for (int index = blockIdx.x*blockDim.x+threadIdx.x; index < numPairs; index += blockDim.x*gridDim.x) {
+    index = GLOBAL_ID;
+    while (index < numPairs){
         int atom1 = pairList[index].x;
         int atom2 = pairList[index].y;
         mixed4 v1 = velm[atom1];
@@ -51,21 +56,27 @@ extern "C" __global__ void integrateVelocityVerletPart1(int numAtoms, int numPai
         relVel.x= v2.x - v1.x;
         relVel.y= v2.y - v1.y;
         relVel.z= v2.z - v1.z;
-        //
+
         mixed3 comFrc;
-        comFrc.x = force[atom1] + force[atom2];
-        comFrc.y = force[atom1 + paddedNumAtoms] + force[atom2 + paddedNumAtoms];
-        comFrc.z = force[atom1 + paddedNumAtoms*2] + force[atom2 + paddedNumAtoms*2];
+        mixed F1x = scale*force[atom1];
+        mixed F1y = scale*force[atom1+paddedNumAtoms];
+        mixed F1z = scale*force[atom1+paddedNumAtoms*2];
+        mixed F2x = scale*force[atom2];
+        mixed F2y = scale*force[atom2+paddedNumAtoms];
+        mixed F2z = scale*force[atom2+paddedNumAtoms*2];
+        comFrc.x = F1x + F2x;
+        comFrc.y = F1y + F2y;
+        comFrc.z = F1z + F2z;
         mixed3 relFrc;
-        relFrc.x = mass1fract*force[atom2] - mass2fract*force[atom1];
-        relFrc.y = mass1fract*force[atom2+paddedNumAtoms] - mass2fract*force[atom1+paddedNumAtoms];
-        relFrc.z = mass1fract*force[atom2+paddedNumAtoms*2] - mass2fract*force[atom1+paddedNumAtoms*2];
-        comVel.x += comFrc.x * scale * invTotMass;
-        comVel.y += comFrc.y * scale * invTotMass;
-        comVel.z += comFrc.z * scale * invTotMass;
-        relVel.x += relFrc.x * scale * invRedMass;
-        relVel.y += relFrc.y * scale * invRedMass;
-        relVel.z += relFrc.z * scale * invRedMass;
+        relFrc.x = mass1fract*F2x - mass2fract*F1x;
+        relFrc.y = mass1fract*F2y - mass2fract*F1y;
+        relFrc.z = mass1fract*F2z - mass2fract*F1z;
+        comVel.x += comFrc.x * invTotMass;
+        comVel.y += comFrc.y * invTotMass;
+        comVel.z += comFrc.z * invTotMass;
+        relVel.x += relFrc.x * invRedMass;
+        relVel.y += relFrc.y * invRedMass;
+        relVel.z += relFrc.z * invRedMass;
 #ifdef USE_MIXED_PRECISION
         real4 posv1 = posq[atom1];
         real4 posv2 = posq[atom2];
@@ -97,22 +108,25 @@ extern "C" __global__ void integrateVelocityVerletPart1(int numAtoms, int numPai
             posDelta[atom2] = pos2;
             velm[atom2] = v2;
         }
+        index += GLOBAL_SIZE;
      }
 }
 
 /**
  * Perform the second step of Velocity Verlet integration.
- * 
- * apply displacements to positions (posq) after constraints have been enforced
  */
 
-extern "C" __global__ void integrateVelocityVerletPart2(int numAtoms, mixed2* __restrict__ dt, real4* __restrict__ posq,
-        real4* __restrict__ posqCorrection, mixed4* __restrict__ velm, const mixed4* __restrict__ posDelta) {
+KERNEL void integrateVelocityVerletPart2(int numAtoms, GLOBAL mixed2* RESTRICT dt, GLOBAL real4* RESTRICT posq, GLOBAL mixed4* RESTRICT velm,
+                                         GLOBAL const mixed4* RESTRICT posDelta
+#ifdef USE_MIXED_PRECISION
+                                        ,GLOBAL real4* RESTRICT posqCorrection
+#endif
+    ){
     mixed2 stepSize = dt[0];
-    int index = blockIdx.x*blockDim.x+threadIdx.x;
+    int index = GLOBAL_ID;
     if (index == 0)
         dt[0].x = stepSize.y;
-    for (; index < numAtoms; index += blockDim.x*gridDim.x) {
+    while(index < numAtoms) {
         mixed4 velocity = velm[index];
         if (velocity.w != 0.0) {
 #ifdef USE_MIXED_PRECISION
@@ -133,21 +147,23 @@ extern "C" __global__ void integrateVelocityVerletPart2(int numAtoms, mixed2* __
             posq[index] = pos;
 #endif
         }
+        index += GLOBAL_SIZE;
     }
 }
 
-
 /**
  * Perform the third step of Velocity Verlet integration.
- *
- * modify the velocities (velm) after the force update
  */
 
-extern "C" __global__ void integrateVelocityVerletPart3(int numAtoms, int numPairs, int paddedNumAtoms, mixed2* __restrict__ dt, real4* __restrict__ posq,
-        real4* __restrict__ posqCorrection, mixed4* __restrict__ velm,  const long long* __restrict__ force, const mixed4* __restrict__ posDelta,
-        const int* __restrict__ atomList, const int2* __restrict__ pairList) {
+KERNEL void integrateVelocityVerletPart3(int numAtoms, int numPairs, int paddedNumAtoms, GLOBAL mixed2* RESTRICT dt, GLOBAL real4* RESTRICT posq,
+                                         GLOBAL mixed4* RESTRICT velm, GLOBAL const mm_long* RESTRICT force, GLOBAL const mixed4* RESTRICT posDelta,
+                                         GLOBAL const int* RESTRICT atomList, GLOBAL const int2* RESTRICT pairList
+#ifdef USE_MIXED_PRECISION
+                                        ,GLOBAL const real4* RESTRICT posqCorrection
+#endif
+    ){
     mixed2 stepSize = dt[0];
-#if __CUDA_ARCH__ >= 130
+#ifdef SUPPORTS_DOUBLE_PRECISION
     double oneOverDt = 1.0/stepSize.y;
 #else
     float oneOverDt = 1.0f/stepSize.y;
@@ -155,11 +171,10 @@ extern "C" __global__ void integrateVelocityVerletPart3(int numAtoms, int numPai
 #endif
     const mixed dtVel = 0.5f*(stepSize.x+stepSize.y);
     const mixed scale = 0.5f*dtVel/(mixed) 0x100000000;
-    int index = blockIdx.x*blockDim.x+threadIdx.x;
+    int index = GLOBAL_ID;
     if (index == 0)
         dt[0].x = stepSize.y;
-
-    for (int index = blockIdx.x*blockDim.x+threadIdx.x; index < numAtoms; index += blockDim.x*gridDim.x) {
+    while(index < numAtoms) {
         int atom = atomList[index];
         mixed4 velocity = velm[atom];
         if (velocity.w != 0.0) {
@@ -167,15 +182,17 @@ extern "C" __global__ void integrateVelocityVerletPart3(int numAtoms, int numPai
             velocity.x += scale*force[atom]*velocity.w + (deltaXconstrained.x - velocity.x*stepSize.y)*oneOverDt;
             velocity.y += scale*force[atom+paddedNumAtoms]*velocity.w + (deltaXconstrained.y - velocity.y*stepSize.y)*oneOverDt;
             velocity.z += scale*force[atom+paddedNumAtoms*2]*velocity.w + (deltaXconstrained.z - velocity.z*stepSize.y)*oneOverDt;
-#if __CUDA_ARCH__ < 130
+#ifndef SUPPORTS_DOUBLE_PRECISION
             velocity.x += (deltaXconstrained.x - velocity.x*stepSize.y)*correction;
             velocity.y += (deltaXconstrained.y - velocity.y*stepSize.y)*correction;
             velocity.z += (deltaXconstrained.z - velocity.z*stepSize.y)*correction;
 #endif
             velm[atom] = velocity;
         }
+        index += GLOBAL_SIZE;
     }
-    for (int index = blockIdx.x*blockDim.x+threadIdx.x; index < numPairs; index += blockDim.x*gridDim.x) {
+    index = GLOBAL_ID;
+    while(index < numPairs) {
         int atom1 = pairList[index].x;
         int atom2 = pairList[index].y;
         mixed4 v1 = velm[atom1];
@@ -194,27 +211,33 @@ extern "C" __global__ void integrateVelocityVerletPart3(int numAtoms, int numPai
         relVel.x= v2.x - v1.x;
         relVel.y= v2.y - v1.y;
         relVel.z= v2.z - v1.z;
-        //
+
         mixed3 comFrc;
-        comFrc.x = force[atom1] + force[atom2];
-        comFrc.y = force[atom1 + paddedNumAtoms] + force[atom2 + paddedNumAtoms];
-        comFrc.z = force[atom1 + paddedNumAtoms*2] + force[atom2 + paddedNumAtoms*2];
+        mixed F1x = scale*force[atom1];
+        mixed F1y = scale*force[atom1+paddedNumAtoms];
+        mixed F1z = scale*force[atom1+paddedNumAtoms*2];
+        mixed F2x = scale*force[atom2];
+        mixed F2y = scale*force[atom2+paddedNumAtoms];
+        mixed F2z = scale*force[atom2+paddedNumAtoms*2];
+        comFrc.x = F1x + F2x;
+        comFrc.y = F1y + F2y;
+        comFrc.z = F1z + F2z;
         mixed3 relFrc;
-        relFrc.x = mass1fract*force[atom2] - mass2fract*force[atom1];
-        relFrc.y = mass1fract*force[atom2+paddedNumAtoms] - mass2fract*force[atom1+paddedNumAtoms];
-        relFrc.z = mass1fract*force[atom2+paddedNumAtoms*2] - mass2fract*force[atom1+paddedNumAtoms*2];
-        comVel.x += comFrc.x * scale * invTotMass;
-        comVel.y += comFrc.y * scale * invTotMass;
-        comVel.z += comFrc.z * scale * invTotMass;
-        relVel.x += relFrc.x * scale * invRedMass;
-        relVel.y += relFrc.y * scale * invRedMass;
-        relVel.z += relFrc.z * scale * invRedMass;
+        relFrc.x = mass1fract*F2x - mass2fract*F1x;
+        relFrc.y = mass1fract*F2y - mass2fract*F1y;
+        relFrc.z = mass1fract*F2z - mass2fract*F1z;
+        comVel.x += comFrc.x * invTotMass;
+        comVel.y += comFrc.y * invTotMass;
+        comVel.z += comFrc.z * invTotMass;
+        relVel.x += relFrc.x * invRedMass;
+        relVel.y += relFrc.y * invRedMass;
+        relVel.z += relFrc.z * invRedMass;
         if (v1.w != 0.0f) {
             mixed4 deltaXconstrained = posDelta[atom1];
             v1.x = comVel.x - relVel.x*mass2fract + (deltaXconstrained.x - v1.x*stepSize.y)*oneOverDt;
             v1.y = comVel.y - relVel.y*mass2fract + (deltaXconstrained.y - v1.y*stepSize.y)*oneOverDt;
             v1.z = comVel.z - relVel.z*mass2fract + (deltaXconstrained.z - v1.z*stepSize.y)*oneOverDt;
-#if __CUDA_ARCH__ < 130
+#ifndef SUPPORTS_DOUBLE_PRECISION
             v1.x += (deltaXconstrained.x - v1.x*stepSize.y)*correction;
             v1.y += (deltaXconstrained.y - v1.y*stepSize.y)*correction;
             v1.z += (deltaXconstrained.z - v1.z*stepSize.y)*correction;
@@ -226,58 +249,57 @@ extern "C" __global__ void integrateVelocityVerletPart3(int numAtoms, int numPai
             v2.x = comVel.x + relVel.x*mass1fract + (deltaXconstrained.x - v2.x*stepSize.y)*oneOverDt;
             v2.y = comVel.y + relVel.y*mass1fract + (deltaXconstrained.y - v2.y*stepSize.y)*oneOverDt;
             v2.z = comVel.z + relVel.z*mass1fract + (deltaXconstrained.z - v2.z*stepSize.y)*oneOverDt;
-#if __CUDA_ARCH__ < 130
+#ifndef SUPPORTS_DOUBLE_PRECISION
             v2.x += (deltaXconstrained.x - v2.x*stepSize.y)*correction;
             v2.y += (deltaXconstrained.y - v2.y*stepSize.y)*correction;
             v2.z += (deltaXconstrained.z - v2.z*stepSize.y)*correction;
 #endif
             velm[atom2] = v2;
         }
+        index += GLOBAL_SIZE;
     }
 }
 
+KERNEL void integrateVelocityVerletHardWall(int numPairs, GLOBAL const float* RESTRICT maxPairDistance, 
+                                            GLOBAL mixed2* RESTRICT dt, GLOBAL real4* RESTRICT posq,
+                                            GLOBAL mixed4* RESTRICT velm, GLOBAL const int2* RESTRICT pairList,
+                                            GLOBAL const float* RESTRICT pairTemperature
+#ifdef USE_MIXED_PRECISION
+                                           ,GLOBAL real4* RESTRICT posqCorrection
+#endif
+    ){
 
-
-/**
- * Apply the hard wall constraint 
- */
-
-extern "C" __global__ void integrateVelocityVerletHardWall(int numPairs, const float* __restrict__ maxPairDistance, mixed2* __restrict__ dt, real4* __restrict__ posq,
-        real4* __restrict__ posqCorrection, mixed4* __restrict__ velm, 
-        const int2* __restrict__ pairList, const float* __restrict__ pairTemperature) {
     mixed dtPos = dt[0].y;
     mixed maxDelta = (mixed) maxPairDistance[0];
-    // Apply hard wall constraints.
-    if (maxDelta > 0) {
-        for (int index = blockIdx.x*blockDim.x+threadIdx.x; index < numPairs; index += blockDim.x*gridDim.x) {
+    if (maxDelta > 0){
+        int index = GLOBAL_ID;
+        while(index < numPairs) {
+
             const mixed hardWallScale = sqrt( ((mixed) pairTemperature[index]) * ((mixed) BOLTZ));
-            int2 atom = make_int2(pairList[index].x, pairList[index].y);
+            int atom1 = pairList[index].x;
+            int atom2 = pairList[index].y;
 #ifdef USE_MIXED_PRECISION
-            real4 posv1 = posq[atom.x];
-            real4 posc1 = posqCorrection[atom.x];
+            real4 posv1 = posq[atom1];
+            real4 posc1 = posqCorrection[atom1];
             mixed4 pos1 = make_mixed4(posv1.x+(mixed)posc1.x, posv1.y+(mixed)posc1.y, posv1.z+(mixed)posc1.z, posv1.w);
-            real4 posv2 = posq[atom.y];
-            real4 posc2 = posqCorrection[atom.y];
+            real4 posv2 = posq[atom2];
+            real4 posc2 = posqCorrection[atom2];
             mixed4 pos2 = make_mixed4(posv2.x+(mixed)posc2.x, posv2.y+(mixed)posc2.y, posv2.z+(mixed)posc2.z, posv2.w);
 #else
-            real4 pos1 = posq[atom.x];
-            real4 pos2 = posq[atom.y];
+            real4 pos1 = posq[atom1];
+            real4 pos2 = posq[atom2];
 #endif
-            mixed3 delta = make_mixed3(
-                mixed (pos1.x - pos2.x),
-                mixed (pos1.y - pos2.y),
-                mixed (pos1.z - pos2.z)
-            );
+            mixed3 delta = make_mixed3(pos1.x - pos2.x, pos1.y - pos2.y, pos1.z - pos2.z);
             mixed r = sqrt(delta.x*delta.x + delta.y*delta.y + delta.z*delta.z);
             mixed rInv = 1/r;
             if (rInv*maxDelta < 1.0) {
                 // The constraint has been violated, so make the inter-particle distance "bounce"
                 // off the hard wall.
                 mixed3 bondDir = make_mixed3(delta.x * rInv, delta.y * rInv, delta.z * rInv);
-                mixed3 vel1 = make_mixed3(velm[atom.x].x, velm[atom.x].y, velm[atom.x].z);
-                mixed3 vel2 = make_mixed3(velm[atom.y].x, velm[atom.y].y, velm[atom.y].z);
-                mixed m1 = velm[atom.x].w != 0.0 ? 1.0/velm[atom.x].w : 0.0;
-                mixed m2 = velm[atom.y].w != 0.0 ? 1.0/velm[atom.y].w : 0.0;
+                mixed3 vel1 = make_mixed3(velm[atom1].x, velm[atom1].y, velm[atom1].z);
+                mixed3 vel2 = make_mixed3(velm[atom2].x, velm[atom2].y, velm[atom2].z);
+                mixed m1 = velm[atom1].w != 0.0 ? 1.0/velm[atom1].w : 0.0;
+                mixed m2 = velm[atom2].w != 0.0 ? 1.0/velm[atom2].w : 0.0;
                 mixed invTotMass = (m1 + m2 != 0.0) ? 1.0 /(m1 + m2) : 0.0;
                 mixed deltaR = r-maxDelta;
                 mixed deltaT = dtPos;
@@ -298,12 +320,12 @@ extern "C" __global__ void integrateVelocityVerletHardWall(int numPairs, const f
                     pos1.x += bondDir.x*dr;
                     pos1.y += bondDir.y*dr;
                     pos1.z += bondDir.z*dr;
-                    velm[atom.x] = make_mixed4(vp1.x + bondDir.x*dotvr1, vp1.y + bondDir.y*dotvr1, vp1.z + bondDir.z*dotvr1, velm[atom.x].w);
+                    velm[atom1] = make_mixed4(vp1.x + bondDir.x*dotvr1, vp1.y + bondDir.y*dotvr1, vp1.z + bondDir.z*dotvr1, velm[atom1].w);
 #ifdef USE_MIXED_PRECISION
-                    posq[atom.x] = make_real4((real) pos1.x, (real) pos1.y, (real) pos1.z, (real) pos1.w);
-                    posqCorrection[atom.x] = make_real4(pos1.x-(real) pos1.x, pos1.y-(real) pos1.y, pos1.z-(real) pos1.z, 0);
+                    posq[atom1] = make_real4((real) pos1.x, (real) pos1.y, (real) pos1.z, (real) pos1.w);
+                    posqCorrection[atom1] = make_real4(pos1.x-(real) pos1.x, pos1.y-(real) pos1.y, pos1.z-(real) pos1.z, 0);
 #else
-                    posq[atom.x] = pos1;
+                    posq[atom1] = pos1;
 #endif
                 }
                 else {
@@ -331,19 +353,21 @@ extern "C" __global__ void integrateVelocityVerletHardWall(int numPairs, const f
                     pos2.x += bondDir.x*dr2;
                     pos2.y += bondDir.y*dr2;
                     pos2.z += bondDir.z*dr2;
-                    velm[atom.x] = make_mixed4(vp1.x + bondDir.x*dotvr1, vp1.y + bondDir.y*dotvr1, vp1.z + bondDir.z*dotvr1, velm[atom.x].w);
-                    velm[atom.y] = make_mixed4(vp2.x + bondDir.x*dotvr2, vp2.y + bondDir.y*dotvr2, vp2.z + bondDir.z*dotvr2, velm[atom.y].w);
+                    velm[atom1] = make_mixed4(vp1.x + bondDir.x*dotvr1, vp1.y + bondDir.y*dotvr1, vp1.z + bondDir.z*dotvr1, velm[atom1].w);
+                    velm[atom2] = make_mixed4(vp2.x + bondDir.x*dotvr2, vp2.y + bondDir.y*dotvr2, vp2.z + bondDir.z*dotvr2, velm[atom2].w);
 #ifdef USE_MIXED_PRECISION
-                    posq[atom.x] = make_real4((real) pos1.x, (real) pos1.y, (real) pos1.z, (real) pos1.w);
-                    posq[atom.y] = make_real4((real) pos2.x, (real) pos2.y, (real) pos2.z, (real) pos2.w);
-                    posqCorrection[atom.x] = make_real4(pos1.x-(real) pos1.x, pos1.y-(real) pos1.y, pos1.z-(real) pos1.z, 0);
-                    posqCorrection[atom.y] = make_real4(pos2.x-(real) pos2.x, pos2.y-(real) pos2.y, pos2.z-(real) pos2.z, 0);
+                    posq[atom1] = make_real4((real) pos1.x, (real) pos1.y, (real) pos1.z, (real) pos1.w);
+                    posq[atom2] = make_real4((real) pos2.x, (real) pos2.y, (real) pos2.z, (real) pos2.w);
+                    posqCorrection[atom1] = make_real4(pos1.x-(real) pos1.x, pos1.y-(real) pos1.y, pos1.z-(real) pos1.z, 0);
+                    posqCorrection[atom2] = make_real4(pos2.x-(real) pos2.x, pos2.y-(real) pos2.y, pos2.z-(real) pos2.z, 0);
 #else
-                    posq[atom.x] = pos1;
-                    posq[atom.y] = pos2;
+                    posq[atom1] = pos1;
+                    posq[atom2] = pos2;
 #endif
                 }
             }
+            index += GLOBAL_SIZE;
+        }
     }
-    } /* end of hard wall constraint part */
 }
+

platforms/cuda/include/CudaKernels.h

@@ -447,109 +447,6 @@ private:
     CUfunction copyStateKernel, copyForcesKernel, addForcesKernel;
 };
 
-/*
- * This kernel is invoked by NoseHooverIntegrator to take one time step.
- */
-class CudaIntegrateVelocityVerletStepKernel : public IntegrateVelocityVerletStepKernel {
-public:
-    CudaIntegrateVelocityVerletStepKernel(std::string name, const Platform& platform, CudaContext& cu) :
-                                  IntegrateVelocityVerletStepKernel(name, platform), cu(cu) { }
-    ~CudaIntegrateVelocityVerletStepKernel() {}
-    /**
-     * Initialize the kernel.
-     * 
-     * @param system     the System this kernel will be applied to
-     * @param integrator the NoseHooverIntegrator this kernel will be used for
-     */
-    void initialize(const System& system, const NoseHooverIntegrator& integrator);
-    /**
-     * Execute the kernel.
-     * 
-     * @param context    the context in which to execute this kernel
-     * @param integrator the VerletIntegrator this kernel is being used for
-     * @param forcesAreValid a reference to the parent integrator's boolean for keeping
-     *                       track of the validity of the current forces.
-     */
-    void execute(ContextImpl& context, const NoseHooverIntegrator& integrator, bool &forcesAreValid);
-    /**
-     * Compute the kinetic energy.
-     * 
-     * @param context    the context in which to execute this kernel
-     * @param integrator the NoseHooverIntegrator this kernel is being used for
-     */
-    double computeKineticEnergy(ContextImpl& context, const NoseHooverIntegrator& integrator);
-private:
-    CudaContext& cu;
-    float prevMaxPairDistance;
-    CudaArray maxPairDistanceBuffer, pairListBuffer, atomListBuffer, pairTemperatureBuffer;
-    CUfunction kernel1, kernel2, kernel3, kernelHardWall;
-};
-
-/**
- * This kernel is invoked by NoseHooverChain at the start of each time step to adjust the thermostat
- * and update the associated particle velocities.
- */
-class CudaNoseHooverChainKernel : public NoseHooverChainKernel {
-public:
-    CudaNoseHooverChainKernel(std::string name, const Platform& platform, CudaContext& cu) : NoseHooverChainKernel(name, platform), cu(cu) {
-    }
-    ~CudaNoseHooverChainKernel() {}
-    /**
-     * Initialize the kernel.
-     */
-    void initialize();
-    /**
-     * Execute the kernel that propagates the Nose Hoover chain and determines the velocity scale factor.
-     * 
-     * @param context  the context in which to execute this kernel
-     * @param noseHooverChain the object describing the chain to be propagated.
-     * @param kineticEnergies the {absolute, relative} kineticEnergy of the particles being thermostated by this chain.
-     * @param timeStep the time step used by the integrator.
-     * @return the {absolute, relative} velocity scale factor to apply to the particles associated with this heat bath.
-     */
-    std::pair<double, double> propagateChain(ContextImpl& context, const NoseHooverChain &nhc, std::pair<double, double> kineticEnergies, double timeStep);
-    /**
-     * Execute the kernal that computes the total (kinetic + potential) heat bath energy.
-     *
-     * @param context the context in which to execute this kernel
-     * @param noseHooverChain the chain whose energy is to be determined.
-     * @return the total heat bath energy.
-     */
-    double computeHeatBathEnergy(ContextImpl& context, const NoseHooverChain &nhc);
-    /**
-     * Execute the kernel that computes the kinetic energy for a subset of atoms,
-     * or the relative kinetic energy of Drude particles with respect to their parent atoms
-     *
-     * @param context the context in which to execute this kernel
-     * @param noseHooverChain the chain whose energy is to be determined.
-     * @param downloadValue whether the computed value should be downloaded and returned.
-     *
-     */
-    std::pair<double,double> computeMaskedKineticEnergy(ContextImpl& context, const NoseHooverChain &noseHooverChain, bool downloadValue);
-
-    /**
-     * Execute the kernel that scales the velocities of particles associated with a nose hoover chain
-     *
-     * @param context the context in which to execute this kernel
-     * @param noseHooverChain the chain whose energy is to be determined.
-     * @param scaleFactors the {absolute, relative} multiplicative factor by which velocities are scaled.
-     */
-    void scaleVelocities(ContextImpl& context, const NoseHooverChain &noseHooverChain, std::pair<double, double> scaleFactors);
-
-private:
-    int sumWorkGroupSize;
-    CudaContext& cu;
-    CudaArray energyBuffer, scaleFactorBuffer, kineticEnergyBuffer, chainMasses, chainForces, heatBathEnergy;
-    std::map<int, CudaArray> atomlists, pairlists;
-    std::map<int, CUfunction> propagateKernels;
-    CUfunction reduceEnergyKernel;
-    CUfunction computeHeatBathEnergyKernel;
-    CUfunction computeAtomsKineticEnergyKernel;
-    CUfunction computePairsKineticEnergyKernel;
-    CUfunction scaleAtomsVelocitiesKernel;
-    CUfunction scalePairsVelocitiesKernel;
-};
-
 /**
  * This kernel is invoked by MonteCarloBarostat to adjust the periodic box volume
  */

platforms/cuda/src/CudaKernelFactory.cpp

@@ -134,9 +134,9 @@ KernelImpl* CudaKernelFactory::createKernelImpl(std::string name, const Platform
     if (name == ApplyAndersenThermostatKernel::Name())
         return new CommonApplyAndersenThermostatKernel(name, platform, cu);
     if (name == NoseHooverChainKernel::Name())
-        return new CudaNoseHooverChainKernel(name, platform, cu);
+        return new CommonNoseHooverChainKernel(name, platform, cu);
     if (name == IntegrateVelocityVerletStepKernel::Name())
-        return new CudaIntegrateVelocityVerletStepKernel(name, platform, cu);
+        return new CommonIntegrateVelocityVerletStepKernel(name, platform, cu);
     if (name == ApplyMonteCarloBarostatKernel::Name())
         return new CudaApplyMonteCarloBarostatKernel(name, platform, cu);
     if (name == RemoveCMMotionKernel::Name())

platforms/cuda/src/CudaKernels.cpp

@@ -1497,118 +1497,6 @@ void CudaCalcNonbondedForceKernel::getLJPMEParameters(double& alpha, int& nx, in
         nz = dispersionGridSizeZ;
     }
 }
-void CudaIntegrateVelocityVerletStepKernel::initialize(const System& system, const NoseHooverIntegrator& integrator) {
-    cu.getPlatformData().initializeContexts(system);
-    cu.setAsCurrent();
-    map<string, string> defines;
-    defines["BOLTZ"] = cu.doubleToString(BOLTZ);
-    CUmodule module = cu.createModule(CudaKernelSources::velocityVerlet, defines, "");
-    kernel1 = cu.getKernel(module, "integrateVelocityVerletPart1");
-    kernel2 = cu.getKernel(module, "integrateVelocityVerletPart2");
-    kernel3 = cu.getKernel(module, "integrateVelocityVerletPart3");
-    kernelHardWall = cu.getKernel(module, "integrateVelocityVerletHardWall");
-    prevMaxPairDistance = -1.0;
-    maxPairDistanceBuffer.initialize<float>(cu, 1, "maxPairDistanceBuffer");
-}
-
-void CudaIntegrateVelocityVerletStepKernel::execute(ContextImpl& context, const NoseHooverIntegrator& integrator, bool &forcesAreValid) {
-    cu.setAsCurrent();
-    CudaIntegrationUtilities& integration = cu.getIntegrationUtilities();
-    int paddedNumAtoms = cu.getPaddedNumAtoms();
-    double dt = integrator.getStepSize();
-    cu.getIntegrationUtilities().setNextStepSize(dt);
-
-    if (!forcesAreValid) context.calcForcesAndEnergy(true, false);
-
-    const auto& atomList = integrator.getAllThermostatedIndividualParticles();
-    const auto& pairList = integrator.getAllThermostatedPairs();
-    int numAtoms = atomList.size();
-    int numPairs = pairList.size();
-    int numParticles = numAtoms + 2*numPairs;
-    float maxPairDistance = integrator.getMaximumPairDistance();
-    // Make sure atom and pair metadata is uploaded and has the correct dimensions
-    if (prevMaxPairDistance != maxPairDistance) {
-        std::vector<float> tmp(1, maxPairDistance);
-        maxPairDistanceBuffer.upload(tmp);
-        prevMaxPairDistance = maxPairDistance;
-    }
-    if (numAtoms !=0 && (!atomListBuffer.isInitialized() || atomListBuffer.getSize() != numAtoms)) {
-        if (atomListBuffer.isInitialized())
-            atomListBuffer.resize(atomList.size());
-        else
-            atomListBuffer.initialize<int>(cu, atomList.size(), "atomListBuffer");
-        atomListBuffer.upload(atomList);
-    }
-    if (numPairs !=0 && (!pairListBuffer.isInitialized() || pairListBuffer.getSize() != numPairs)) {
-        if (pairListBuffer.isInitialized()) {
-            pairListBuffer.resize(pairList.size());
-            pairTemperatureBuffer.resize(pairList.size());
-        }
-        else {
-            pairListBuffer.initialize<int2>(cu, pairList.size(), "pairListBuffer");
-            pairTemperatureBuffer.initialize<float>(cu, pairList.size(), "pairTemperatureBuffer");
-        }
-        std::vector<int2> tmp;
-        std::vector<float> tmp2;
-        for(const auto &pair : pairList) {
-            tmp.push_back(make_int2(std::get<0>(pair), std::get<1>(pair)));
-            tmp2.push_back(std::get<2>(pair));
-        }
-        pairListBuffer.upload(tmp);
-        pairTemperatureBuffer.upload(tmp2);
-    }
-    //// Call the first integration kernel.
-
-    CUdeviceptr posCorrection = (cu.getUseMixedPrecision() ? cu.getPosqCorrection().getDevicePointer() : 0);
-    void* args1[] = {&numAtoms, &numPairs, &paddedNumAtoms, &cu.getIntegrationUtilities().getStepSize().getDevicePointer(), &cu.getPosq().getDevicePointer(), &posCorrection,
-            &cu.getVelm().getDevicePointer(), &cu.getForce().getDevicePointer(), &integration.getPosDelta().getDevicePointer(),
-            &atomListBuffer.getDevicePointer(), &pairListBuffer.getDevicePointer()};
-    cu.executeKernel(kernel1, args1, std::max(numAtoms,numPairs), 128);
-
-    //// Apply constraints.
-
-    integration.applyConstraints(integrator.getConstraintTolerance());
-
-    //// Call the second integration kernel.
-    void* args2[] = {&numParticles, &cu.getIntegrationUtilities().getStepSize().getDevicePointer(), &cu.getPosq().getDevicePointer(), &posCorrection,
-            &cu.getVelm().getDevicePointer(), &integration.getPosDelta().getDevicePointer()};
-    cu.executeKernel(kernel2, args2, numParticles, 128);
-
-    if (numPairs > 0) {
-        //// Enforce hard wall constraint
-        void* argsHardWall[] = {&numPairs, &maxPairDistanceBuffer.getDevicePointer(), 
-                 &cu.getIntegrationUtilities().getStepSize().getDevicePointer(), &cu.getPosq().getDevicePointer(), &posCorrection,
-                 &cu.getVelm().getDevicePointer(), &pairListBuffer.getDevicePointer(), 
-                 &pairTemperatureBuffer.getDevicePointer()}; 
-        cu.executeKernel(kernelHardWall, argsHardWall, numPairs, 128);
-    }
-
-    integration.computeVirtualSites();
-
-    //// Update forces
-    context.calcForcesAndEnergy(true, false);
-    forcesAreValid = true;
-
-    //// Call the third integration kernel.
-    void* args3[] = {&numAtoms, &numPairs, &paddedNumAtoms, &cu.getIntegrationUtilities().getStepSize().getDevicePointer(), &cu.getPosq().getDevicePointer(), &posCorrection,
-            &cu.getVelm().getDevicePointer(), &cu.getForce().getDevicePointer(), &integration.getPosDelta().getDevicePointer(),
-            &atomListBuffer.getDevicePointer(), &pairListBuffer.getDevicePointer()};
-    cu.executeKernel(kernel3, args3, std::max(numAtoms,numPairs), 128);
-
-    // TODO: Figure out if this is really needed.  The constraint velocities are accounted for
-    // in a finite difference sense in the step 3 kernel, when the velocities are updated.
-    integration.applyVelocityConstraints(integrator.getConstraintTolerance());
-
-    //// Update the time and step count.
-
-    cu.setTime(cu.getTime()+dt);
-    cu.setStepCount(cu.getStepCount()+1);
-    cu.reorderAtoms();
-}
-
-double CudaIntegrateVelocityVerletStepKernel::computeKineticEnergy(ContextImpl& context, const NoseHooverIntegrator& integrator) {
-    return cu.getIntegrationUtilities().computeKineticEnergy(0);
-}
 
 class CudaCalcCustomCVForceKernel::ForceInfo : public CudaForceInfo {
 public:
@@ -1820,357 +1708,6 @@ void CudaCalcCustomCVForceKernel::copyParametersToContext(ContextImpl& context,
         delete function.second;
 }
 
-void CudaNoseHooverChainKernel::initialize() {
-    cu.setAsCurrent();
-    bool useDouble = cu.getUseDoublePrecision() || cu.getUseMixedPrecision();
-    map<string, string> defines;
-    sumWorkGroupSize = 512;
-    defines["WORK_GROUP_SIZE"] = cu.intToString(sumWorkGroupSize);
-    defines["MIXEDEXP"] = useDouble ? "exp" : "expf";
-    defines["BEGIN_YS_LOOP"] = "for(const real & ys : {1}) {";
-    defines["END_YS_LOOP"] = "}";
-    CUmodule module = cu.createModule(CudaKernelSources::noseHooverChain, defines, "-std=c++11");
-    propagateKernels[1] = cu.getKernel(module, "propagateNoseHooverChain");
-    defines["BEGIN_YS_LOOP"] = "for(const real & ys : {0.828981543588751, -0.657963087177502, 0.828981543588751}) {";
-    module = cu.createModule(CudaKernelSources::noseHooverChain, defines, "-std=c++11");
-    propagateKernels[3] = cu.getKernel(module, "propagateNoseHooverChain");
-    defines["BEGIN_YS_LOOP"] = "for(const real & ys : {0.2967324292201065, 0.2967324292201065, -0.186929716880426, 0.2967324292201065, 0.2967324292201065}) {";
-    module = cu.createModule(CudaKernelSources::noseHooverChain, defines, "-std=c++11");
-    propagateKernels[5] = cu.getKernel(module, "propagateNoseHooverChain");
-    module = cu.createModule(CudaKernelSources::noseHooverChain, defines, "-std=c++11");
-    reduceEnergyKernel = cu.getKernel(module, "reduceEnergyPair");
-
-    computeHeatBathEnergyKernel = cu.getKernel(module, "computeHeatBathEnergy");
-    computeAtomsKineticEnergyKernel = cu.getKernel(module, "computeAtomsKineticEnergy");
-    computePairsKineticEnergyKernel = cu.getKernel(module, "computePairsKineticEnergy");
-    scaleAtomsVelocitiesKernel = cu.getKernel(module, "scaleAtomsVelocities");
-    scalePairsVelocitiesKernel = cu.getKernel(module, "scalePairsVelocities");
-
-    int energyBufferSize = cu.getEnergyBuffer().getSize();
-    if (cu.getUseDoublePrecision() || cu.getUseMixedPrecision())
-        energyBuffer.initialize<double2>(cu, energyBufferSize, "energyBuffer");
-    else
-        energyBuffer.initialize<float2>(cu, energyBufferSize, "energyBuffer");
-}
-
-std::pair<double, double> CudaNoseHooverChainKernel::propagateChain(ContextImpl& context, const NoseHooverChain &nhc, std::pair<double, double> kineticEnergies, double timeStep) {
-    cu.setAsCurrent();
-
-    bool useDouble = cu.getUseDoublePrecision() || cu.getUseMixedPrecision();
-
-    int chainID = nhc.getChainID();
-    int nAtoms = nhc.getThermostatedAtoms().size();
-    int nPairs = nhc.getThermostatedPairs().size();
-    int chainLength = nhc.getChainLength();
-    int numYS = nhc.getNumYoshidaSuzukiTimeSteps();
-    int numMTS = nhc.getNumMultiTimeSteps();
-    int numDOFs = nhc.getNumDegreesOfFreedom();
-    double temperature = nhc.getTemperature();
-    double frequency = nhc.getCollisionFrequency();
-    double relativeTemperature = nhc.getRelativeTemperature();
-    double relativeFrequency = nhc.getRelativeCollisionFrequency();
-
-    if (numYS != 1 && numYS != 3 && numYS != 5) {
-        throw OpenMMException("Number of Yoshida Suzuki time steps has to be 1, 3, or 5.");
-    }
-
-    auto & chainState = cu.getIntegrationUtilities().getNoseHooverChainState();
-
-    if (!scaleFactorBuffer.isInitialized() || scaleFactorBuffer.getSize() == 0) {
-        if (useDouble) {
-            std::vector<double2> zeros{{0,0}};
-            if (scaleFactorBuffer.isInitialized())
-                scaleFactorBuffer.resize(1);
-            else
-                scaleFactorBuffer.initialize<double2>(cu, 1, "scaleFactorBuffer");
-            scaleFactorBuffer.upload(zeros);
-        }
-        else {
-            std::vector<float2> zeros{{0,0}};
-            if (scaleFactorBuffer.isInitialized())
-                scaleFactorBuffer.resize(1);
-            else
-                scaleFactorBuffer.initialize<float2>(cu, 1, "scaleFactorBuffer");
-            scaleFactorBuffer.upload(zeros);
-        }
-    }
-    std::vector<double> zeros(chainLength,0);
-    if (!chainForces.isInitialized() || !chainMasses.isInitialized()) {
-        if (useDouble) {
-            if (chainForces.isInitialized()) {
-                chainMasses.resize(chainLength);
-                chainForces.resize(chainLength);
-            }
-            else {
-                chainMasses.initialize<double>(cu, chainLength, "chainMasses");
-                chainForces.initialize<double>(cu, chainLength, "chainForces");
-            }
-            chainMasses.upload(zeros);
-            chainForces.upload(zeros);
-        }
-        else {
-            if (chainForces.isInitialized()) {
-                chainMasses.resize(chainLength);
-                chainForces.resize(chainLength);
-            }
-            else {
-                chainMasses.initialize<float>(cu, chainLength, "chainMasses");
-                chainForces.initialize<float>(cu, chainLength, "chainForces");
-            }
-            chainMasses.upload(zeros, true);
-            chainForces.upload(zeros, true);
-        }
-    }
-    if (chainForces.getSize() < chainLength)
-        chainMasses.resize(chainLength);
-    if (chainMasses.getSize() < chainLength)
-        chainMasses.resize(chainLength);
-
-    float timeStepFloat = (float) timeStep;
-    // N.B. We ignore the incoming kineticEnergy and grab it from the device buffer instead
-    if (nAtoms) {
-        if (!chainState.count(2*chainID))
-            chainState[2*chainID] = ComputeArray();
-        if (!chainState.at(2*chainID).isInitialized() || chainState.at(2*chainID).getSize() != chainLength) {
-            // We need to upload the CUDA array
-            if (useDouble) {
-                if (chainState.at(2*chainID).isInitialized())
-                    chainState.at(2*chainID).resize(chainLength);
-                else
-                    chainState.at(2*chainID).initialize<double2>(cu, chainLength, "chainState" + std::to_string(2*chainID));
-                std::vector<double2> zeros(chainLength, make_double2(0, 0));
-                chainState.at(2*chainID).upload(zeros.data());
-            }
-            else {
-                if (chainState.at(2*chainID).isInitialized())
-                    chainState.at(2*chainID).resize(chainLength);
-                else
-                    chainState.at(2*chainID).initialize<float2>(cu, chainLength, "chainState" + std::to_string(2*chainID));
-                std::vector<float2> zeros(chainLength, make_float2(0, 0));
-                chainState.at(2*chainID).upload(zeros.data());
-            }
-        }
-        int chainType = 0;
-        double kT = BOLTZ * temperature;
-        float kTfloat = (float) kT;
-        float frequencyFloat = (float) frequency;
-        void *args[] = {
-                    &cu.unwrap(chainState[2*chainID]).getDevicePointer(),
-                    &kineticEnergyBuffer.getDevicePointer(),
-                    &scaleFactorBuffer.getDevicePointer(),
-                    &chainMasses.getDevicePointer(),
-                    &chainForces.getDevicePointer(),
-                    &chainType, &chainLength, &numMTS, &numDOFs,
-                    &timeStepFloat,
-                    useDouble ? (void*) &kT : (void*) &kTfloat, 
-                    &frequencyFloat
-                    };
-        cu.executeKernel(propagateKernels[numYS], args, 1, 1);
-    }
-    if (nPairs) {
-        if (!chainState.count(2*chainID+1))
-            chainState[2*chainID+1] = ComputeArray();
-        if (!chainState.at(2*chainID+1).isInitialized() || chainState.at(2*chainID+1).getSize() != chainLength) {
-            // We need to upload the CUDA array
-            if (useDouble) {
-                if (chainState.at(2*chainID+1).isInitialized())
-                    chainState.at(2*chainID+1).resize(chainLength);
-                else
-                    chainState.at(2*chainID+1).initialize<double2>(cu, chainLength, "chainState" + std::to_string(2*chainID+1));
-                std::vector<double2> zeros(chainLength, make_double2(0, 0));
-                chainState.at(2*chainID+1).upload(zeros.data());
-            }
-            else {
-                if (chainState.at(2*chainID+1).isInitialized())
-                    chainState.at(2*chainID+1).resize(chainLength);
-                else
-                    chainState.at(2*chainID+1).initialize<float2>(cu, chainLength, "chainState" + std::to_string(2*chainID+1));
-                std::vector<float2> zeros(chainLength, make_float2(0, 0));
-                chainState.at(2*chainID+1).upload(zeros.data());
-            }
-        }
-        int chainType = 1;
-        double kT = BOLTZ * relativeTemperature;
-        int ndf = 3*nPairs;
-        float kTfloat = (float) kT;
-        float frequencyFloat = (float) relativeFrequency;
-        void *args[] = {
-                    &cu.unwrap(chainState[2*chainID+1]).getDevicePointer(),
-                    &kineticEnergyBuffer.getDevicePointer(),
-                    &scaleFactorBuffer.getDevicePointer(),
-                    &chainMasses.getDevicePointer(),
-                    &chainForces.getDevicePointer(),
-                    &chainType, &chainLength, &numMTS, &ndf,
-                    &timeStepFloat,
-                    useDouble ? (void*) &kT : (void*) &kTfloat, 
-                    &frequencyFloat
-                    };
-        cu.executeKernel(propagateKernels[numYS], args, 1, 1);
-    }
-    return {0, 0};
-}
-
-double CudaNoseHooverChainKernel::computeHeatBathEnergy(ContextImpl& context, const NoseHooverChain &nhc) {
-    cu.setAsCurrent();
-
-    bool useDouble = cu.getUseDoublePrecision() || cu.getUseMixedPrecision();
-
-    int chainID = nhc.getChainID();
-    int chainLength = nhc.getChainLength();
-
-    auto & chainState = cu.getIntegrationUtilities().getNoseHooverChainState();
-
-    bool absChainIsValid = chainState.count(2*chainID) != 0 &&
-                           chainState[2*chainID].isInitialized() &&
-                           chainState[2*chainID].getSize() == chainLength;
-    bool relChainIsValid = chainState.count(2*chainID+1) != 0 &&
-                           chainState[2*chainID+1].isInitialized() &&
-                           chainState[2*chainID+1].getSize() == chainLength;
-
-    if (!absChainIsValid && !relChainIsValid) return 0.0;
-
-    if (!heatBathEnergy.isInitialized() || heatBathEnergy.getSize() == 0) {
-        if (useDouble) {
-            std::vector<double> one(1);
-            heatBathEnergy.initialize<double>(cu, 1, "heatBathEnergy");
-            heatBathEnergy.upload(one);
-        }
-        else {
-            std::vector<float> one(1);
-            heatBathEnergy.initialize<float>(cu, 1, "heatBathEnergy");
-            heatBathEnergy.upload(one);
-        }
-    }
-
-    cu.clearBuffer(heatBathEnergy);
-
-    if (absChainIsValid) {
-        int numDOFs = nhc.getNumDegreesOfFreedom();
-        double temperature = nhc.getTemperature();
-        double frequency = nhc.getCollisionFrequency();
-        double kT = BOLTZ * temperature;
-        float kTfloat = (float) kT;
-        float frequencyFloat = (float) frequency;
-
-        void * args[] = {&heatBathEnergy.getDevicePointer(), &chainLength, &numDOFs, 
-                         useDouble ? (void*) &kT : (void*) & kTfloat,
-                         &frequencyFloat, &cu.unwrap(chainState[2*chainID]).getDevicePointer()};
-        cu.executeKernel(computeHeatBathEnergyKernel, args, 1, 1);
-    }
-    if (relChainIsValid) {
-        int numDOFs = 3 * nhc.getThermostatedPairs().size();
-        double temperature = nhc.getRelativeTemperature();
-        double frequency = nhc.getRelativeCollisionFrequency();
-        double kT = BOLTZ * temperature;
-        float kTfloat = (float) kT;
-        float frequencyFloat = (float) frequency;
-
-        void * args[] = {&heatBathEnergy.getDevicePointer(), &chainLength, &numDOFs, 
-                         useDouble ? (void*) &kT : (void*) & kTfloat,
-                         &frequencyFloat, &cu.unwrap(chainState[2*chainID+1]).getDevicePointer()};
-        cu.executeKernel(computeHeatBathEnergyKernel, args, 1, 1);
-    }
-
-
-    void * pinnedBuffer = cu.getPinnedBuffer();
-    heatBathEnergy.download(pinnedBuffer);
-    if (useDouble)
-        return *((double*) pinnedBuffer);
-    else
-        return *((float*) pinnedBuffer);
-}
-
-std::pair<double, double> CudaNoseHooverChainKernel::computeMaskedKineticEnergy(ContextImpl& context, const NoseHooverChain &nhc, bool downloadValue) {
-    cu.setAsCurrent();
-
-    bool useDouble = cu.getUseDoublePrecision() || cu.getUseMixedPrecision();
-
-    int chainID = nhc.getChainID();
-    const auto & nhcAtoms = nhc.getThermostatedAtoms();
-    const auto & nhcPairs = nhc.getThermostatedPairs();
-    auto nAtoms = nhcAtoms.size();
-    auto nPairs = nhcPairs.size();
-    if (nAtoms) {
-        if (!atomlists.count(chainID)) { 
-            // We need to upload the CUDA array
-            atomlists[chainID] = CudaArray();
-            atomlists[chainID].initialize<int>(cu, nAtoms, "atomlist" + std::to_string(chainID));
-            atomlists[chainID].upload(nhcAtoms);
-        }
-        if (atomlists[chainID].getSize() != nAtoms) {
-            throw OpenMMException("Number of atoms changed. Cannot be handled by the same Nose-Hoover thermostat.");
-        }
-    }
-    if (nPairs) {
-        if (!pairlists.count(chainID)) { 
-            // We need to upload the CUDA array
-            pairlists[chainID] = CudaArray();
-            pairlists[chainID].initialize<int2>(cu, nPairs, "pairlist" + std::to_string(chainID));
-            std::vector<int2> int2vec;
-            for(const auto &p : nhcPairs) int2vec.push_back(make_int2(p.first, p.second));
-            pairlists[chainID].upload(int2vec);
-        }
-        if (pairlists[chainID].getSize() != nPairs) {
-            throw OpenMMException("Number of thermostated pairs changed. Cannot be handled by the same Nose-Hoover thermostat.");
-        }
-    }
-    if (!kineticEnergyBuffer.isInitialized() || kineticEnergyBuffer.getSize() == 0) {
-        if (useDouble) {
-            std::vector<double2> zeros{{0,0}};
-            kineticEnergyBuffer.initialize<double2>(cu, 1, "kineticEnergyBuffer");
-            kineticEnergyBuffer.upload(zeros);
-        }
-        else {
-            std::vector<float2> zeros{{0,0}};
-            kineticEnergyBuffer.initialize<float2>(cu, 1, "kineticEnergyBuffer");
-            kineticEnergyBuffer.upload(zeros);
-        }
-    }
-    cu.clearBuffer(energyBuffer);
-    if (nAtoms) {
-        void *args[] = {&energyBuffer.getDevicePointer(),&nAtoms, &cu.getVelm().getDevicePointer(), &atomlists[chainID].getDevicePointer()};
-        cu.executeKernel(computeAtomsKineticEnergyKernel, args, nAtoms);
-    }
-    if (nPairs) {
-        void *args[] = {&energyBuffer.getDevicePointer(),&nPairs, &cu.getVelm().getDevicePointer(), &pairlists[chainID].getDevicePointer()};
-        cu.executeKernel(computePairsKineticEnergyKernel, args, nPairs);
-    }
-
-    //taken from CudaContext::reduceEnergy(); the final kinetic energy will live in the kineticEnergy buffer
-    int bufferSize = energyBuffer.getSize();
-    void* args2[] = {&energyBuffer.getDevicePointer(), &kineticEnergyBuffer.getDevicePointer(), &bufferSize, &sumWorkGroupSize};
-    cu.executeKernel(reduceEnergyKernel, args2, sumWorkGroupSize, sumWorkGroupSize, sumWorkGroupSize*energyBuffer.getElementSize());
-
-    std::pair<double, double> KEs = {0, 0};
-    if (downloadValue) {
-        void * pinnedBuffer = cu.getPinnedBuffer();
-        kineticEnergyBuffer.download(pinnedBuffer);
-        KEs.first = useDouble ? *((double*) pinnedBuffer) : *((float*) pinnedBuffer);
-        KEs.second = useDouble ? *((double*) pinnedBuffer + 1) : *((float*) pinnedBuffer + 1);
-    }
-    return KEs;
-}
-
-void CudaNoseHooverChainKernel::scaleVelocities(ContextImpl& context, const NoseHooverChain &nhc, std::pair<double, double> scaleFactor) {
-    // For now we assume that the atoms and pairs info is valid, because compute{Atoms|Pairs}KineticEnergy must have been
-    // called before this kernel.  If that ever ceases to be true, some sanity checks are needed here.
-    cu.setAsCurrent();
-
-    int chainID = nhc.getChainID();
-    auto nAtoms = nhc.getThermostatedAtoms().size();
-    auto nPairs = nhc.getThermostatedPairs().size();
-    if (nAtoms) {
-        void *args[] = {&scaleFactorBuffer.getDevicePointer(),
-                        &nAtoms, &cu.getVelm().getDevicePointer(), &atomlists[chainID].getDevicePointer()};
-        cu.executeKernel(scaleAtomsVelocitiesKernel, args, nAtoms);
-    }
-    if (nPairs) {
-        void *args[] = {&scaleFactorBuffer.getDevicePointer(),
-                        &nPairs, &cu.getVelm().getDevicePointer(), &pairlists[chainID].getDevicePointer()};
-        cu.executeKernel(scalePairsVelocitiesKernel, args, nPairs);
-    }
-}
-
 void CudaApplyMonteCarloBarostatKernel::initialize(const System& system, const Force& thermostat) {
     cu.setAsCurrent();
     savedPositions.initialize(cu, cu.getPaddedNumAtoms(), cu.getUseDoublePrecision() ? sizeof(double4) : sizeof(float4), "savedPositions");

platforms/cuda/src/kernels/noseHooverChain.cu

-
-#include <initializer_list>
-
-extern "C" __global__ void propagateNoseHooverChain(mixed2* __restrict__ chainData, const mixed2 * __restrict__ energySum, mixed2* __restrict__ scaleFactor,
-                                                    mixed* __restrict__ chainMasses, mixed* __restrict__ chainForces, 
-                                                    int chainType, int chainLength, int numMTS, int numDOFs, float timeStep,
-                                                    mixed kT, float frequency){
-    const mixed & kineticEnergy = chainType ? energySum[0].y : energySum[0].x;
-    mixed &scale = chainType ? scaleFactor[0].y : scaleFactor[0].x;
-    scale = (mixed) 1;
-    if(kineticEnergy < 1e-8) return;
-    for (int bead = 0; bead < chainLength; ++bead) chainMasses[bead] = kT / (frequency * frequency);
-    chainMasses[0] *= numDOFs;
-    mixed KE2 = 2.0f * kineticEnergy;
-    mixed timeOverMTS = timeStep / numMTS;
-    chainForces[0] = (KE2 - numDOFs * kT) / chainMasses[0];
-    for (int bead = 0; bead < chainLength - 1; ++bead) {
-        chainForces[bead + 1] = (chainMasses[bead] * chainData[bead].y * chainData[bead].y - kT) / chainMasses[bead + 1];
-    }
-    for (int mts = 0; mts < numMTS; ++mts) {
-        BEGIN_YS_LOOP
-            mixed wdt = ys * timeOverMTS;
-            chainData[chainLength-1].y += 0.25f * wdt * chainForces[chainLength-1];
-            for (int bead = chainLength - 2; bead >= 0; --bead) {
-                mixed aa = MIXEDEXP(-0.125f * wdt * chainData[bead + 1].y);
-                chainData[bead].y = aa * (chainData[bead].y * aa + 0.25f * wdt * chainForces[bead]);
-            }
-            // update particle velocities
-            mixed aa = MIXEDEXP(-0.5f * wdt * chainData[0].y);
-            scale *= aa;
-            // update the thermostat positions
-            for (int bead = 0; bead < chainLength; ++bead) {
-                chainData[bead].x += 0.5f * chainData[bead].y * wdt;
-            }
-            // update the forces
-            chainForces[0] = (scale * scale * KE2 - numDOFs * kT) / chainMasses[0];
-            // update thermostat velocities
-            for (int bead = 0; bead < chainLength - 1; ++bead) {
-                mixed aa = MIXEDEXP(-0.125f * wdt * chainData[bead + 1].y);
-                chainData[bead].y = aa * (aa * chainData[bead].y + 0.25f * wdt * chainForces[bead]);
-                chainForces[bead + 1] = (chainMasses[bead] * chainData[bead].y * chainData[bead].y - kT) / chainMasses[bead + 1];
-            }
-            chainData[chainLength-1].y += 0.25f * wdt * chainForces[chainLength-1];
-        END_YS_LOOP
-    } // MTS loop
-}
-
-
-/**
- * Compute total (potential + kinetic) energy of the Nose-Hoover beads
- */
-extern "C" __global__ void computeHeatBathEnergy(mixed* __restrict__ heatBathEnergy, int chainLength, int numDOFs,
-                                                 mixed kT, float frequency, const mixed2* __restrict__ chainData){
-    // Note that this is always incremented; make sure it's zeroed properly before the first call
-    mixed &energy = heatBathEnergy[0];
-
-    for(int i = 0; i < chainLength; ++i) {
-        mixed prefac = i ? 1 : numDOFs;
-        mixed mass = prefac * kT / (frequency * frequency);
-        mixed velocity = chainData[i].y; 
-        // The kinetic energy of this bead
-        energy += 0.5f * mass * velocity * velocity;
-        // The potential energy of this bead
-        mixed position = chainData[i].x;
-        energy += prefac * kT * position;
-    }
-}
-
-extern "C" __global__ void computeAtomsKineticEnergy(mixed2 * __restrict__ energyBuffer, int numAtoms,
-                                                     const mixed4* __restrict__ velm, const int *__restrict__ atoms){
-    mixed2 energy = make_mixed2(0,0);
-    //energy = 1; return;
-    for (int index = blockIdx.x*blockDim.x+threadIdx.x; index < numAtoms; index += blockDim.x*gridDim.x) {
-        int atom = atoms[index];
-        mixed4 v = velm[atom];
-        mixed mass = v.w == 0 ? 0 : 1 / v.w;
-        energy.x += 0.5f * mass * (v.x*v.x + v.y*v.y + v.z*v.z);
-    }
-    energyBuffer[blockIdx.x*blockDim.x+threadIdx.x] = energy;
-}
-
-extern "C" __global__ void computePairsKineticEnergy(mixed2 * __restrict__ energyBuffer, int numPairs,
-                                                     const mixed4* __restrict__ velm, const int2 *__restrict__ pairs){
-    mixed2 energy = make_mixed2(0,0);
-    for (int index = blockIdx.x*blockDim.x+threadIdx.x; index < numPairs; index += blockDim.x*gridDim.x) {
-        int2 pair = pairs[index];
-        int atom1 = pair.x;
-        int atom2 = pair.y;
-        mixed4 v1 = velm[atom1];
-        mixed4 v2 = velm[atom2];
-        mixed m1 = v1.w == 0 ? 0 : 1 / v1.w;
-        mixed m2 = v2.w == 0 ? 0 : 1 / v2.w;
-        mixed4 cv;
-        cv.x = (m1*v1.x + m2*v2.x) / (m1 + m2);
-        cv.y = (m1*v1.y + m2*v2.y) / (m1 + m2);
-        cv.z = (m1*v1.z + m2*v2.z) / (m1 + m2);
-        mixed4 rv;
-        rv.x = v2.x - v1.x;
-        rv.y = v2.y - v1.y;
-        rv.z = v2.z - v1.z;
-        energy.x += 0.5f * (m1 + m2) * (cv.x*cv.x + cv.y*cv.y + cv.z*cv.z);
-        energy.y += 0.5f * (m1 * m2 / (m1 + m2)) * (rv.x*rv.x + rv.y*rv.y + rv.z*rv.z);
-    }
-    // The atoms version of this has been called already, so accumulate instead of assigning here
-    energyBuffer[blockIdx.x*blockDim.x+threadIdx.x].x += energy.x;
-    energyBuffer[blockIdx.x*blockDim.x+threadIdx.x].y += energy.y;
-}
-
-extern "C" __global__ void scaleAtomsVelocities(mixed2* __restrict__ scaleFactor, int numAtoms,
-                                                mixed4* __restrict__ velm, const int *__restrict__ atoms){
-    const mixed &scale = scaleFactor[0].x;
-    for (int index = blockIdx.x*blockDim.x+threadIdx.x; index < numAtoms; index += blockDim.x*gridDim.x) {
-        int atom = atoms[index];
-        mixed4 &v = velm[atom];
-        v.x *= scale;
-        v.y *= scale;
-        v.z *= scale;
-    }
-}
-
-extern "C" __global__ void scalePairsVelocities(mixed2 * __restrict__ scaleFactor, int numPairs,
-                                                mixed4* __restrict__ velm, const int2 *__restrict__ pairs){
-    const mixed &absScale = scaleFactor[0].x;
-    const mixed &relScale = scaleFactor[0].y;
-    for (int index = blockIdx.x*blockDim.x+threadIdx.x; index < numPairs; index += blockDim.x*gridDim.x) {
-        int atom1 = pairs[index].x;
-        int atom2 = pairs[index].y;
-        mixed4 v1 = velm[atom1];
-        mixed4 v2 = velm[atom2];
-        mixed m1 = v1.w == 0 ? 0 : 1 / v1.w;
-        mixed m2 = v2.w == 0 ? 0 : 1 / v2.w;
-        mixed4 cv;
-        cv.x = (m1*v1.x + m2*v2.x) / (m1 + m2);
-        cv.y = (m1*v1.y + m2*v2.y) / (m1 + m2);
-        cv.z = (m1*v1.z + m2*v2.z) / (m1 + m2);
-        mixed4 rv;
-        rv.x = v2.x - v1.x;
-        rv.y = v2.y - v1.y;
-        rv.z = v2.z - v1.z;
-        v1.x = absScale * cv.x - relScale * rv.x * m2 / (m1 + m2);
-        v1.y = absScale * cv.y - relScale * rv.y * m2 / (m1 + m2);
-        v1.z = absScale * cv.z - relScale * rv.z * m2 / (m1 + m2);
-        v2.x = absScale * cv.x + relScale * rv.x * m1 / (m1 + m2);
-        v2.y = absScale * cv.y + relScale * rv.y * m1 / (m1 + m2);
-        v2.z = absScale * cv.z + relScale * rv.z * m1 / (m1 + m2);
-        velm[atom1] = v1;
-        velm[atom2] = v2;
-    }
-}
-
-/**
- * Sum the energy buffer containing a pair of energies stored as mixed2.  This is copied from utilities.cu with small modifications
- */
-extern "C" __global__ void reduceEnergyPair(const mixed2* __restrict__ energyBuffer, mixed2* __restrict__ result, int bufferSize, int workGroupSize) {
-    __shared__ mixed2 tempBuffer[WORK_GROUP_SIZE];
-    const unsigned int thread = threadIdx.x;
-    mixed2 sum = make_mixed2(0,0);
-    for (unsigned int idx = thread; idx < bufferSize; idx += blockDim.x) {
-        sum.x += energyBuffer[idx].x;
-        sum.y += energyBuffer[idx].y;
-    }
-    tempBuffer[thread] = sum;
-    for (int i = 1; i < workGroupSize; i *= 2) {
-        __syncthreads();
-        if (thread%(i*2) == 0 && thread+i < workGroupSize) {
-            tempBuffer[thread].x += tempBuffer[thread+i].x;
-            tempBuffer[thread].y += tempBuffer[thread+i].y;
-        }
-    }
-    if (thread == 0)
-        *result = tempBuffer[0];
-}

platforms/opencl/include/OpenCLKernels.h

@@ -428,109 +428,6 @@ private:
     cl::Kernel copyStateKernel, copyForcesKernel, addForcesKernel;
 };
 
-/*
- * This kernel is invoked by NoseHooverIntegrator to take one time step.
- */
-class OpenCLIntegrateVelocityVerletStepKernel : public IntegrateVelocityVerletStepKernel {
-public:
-    OpenCLIntegrateVelocityVerletStepKernel(std::string name, const Platform& platform, OpenCLContext& cl) :
-                                  IntegrateVelocityVerletStepKernel(name, platform), cl(cl) { }
-    ~OpenCLIntegrateVelocityVerletStepKernel() {}
-    /**
-     * Initialize the kernel.
-     * 
-     * @param system     the System this kernel will be applied to
-     * @param integrator the NoseHooverIntegrator this kernel will be used for
-     */
-    void initialize(const System& system, const NoseHooverIntegrator& integrator);
-    /**
-     * Execute the kernel.
-     * 
-     * @param context    the context in which to execute this kernel
-     * @param integrator the VerletIntegrator this kernel is being used for
-     * @param forcesAreValid a reference to the parent integrator's boolean for keeping
-     *                       track of the validity of the current forces.
-     */
-    void execute(ContextImpl& context, const NoseHooverIntegrator& integrator, bool &forcesAreValid);
-    /**
-     * Compute the kinetic energy.
-     * 
-     * @param context    the context in which to execute this kernel
-     * @param integrator the NoseHooverIntegrator this kernel is being used for
-     */
-    double computeKineticEnergy(ContextImpl& context, const NoseHooverIntegrator& integrator);
-private:
-    OpenCLContext& cl;
-    float prevMaxPairDistance;
-    OpenCLArray maxPairDistanceBuffer, pairListBuffer, atomListBuffer, pairTemperatureBuffer; 
-    cl::Kernel kernel1, kernel2, kernel3, kernelHardWall;
-};
-
-/**
- * This kernel is invoked by NoseHooverChain at the start of each time step to adjust the thermostat
- * and update the associated particle velocities.
- */
-class OpenCLNoseHooverChainKernel : public NoseHooverChainKernel {
-public:
-    OpenCLNoseHooverChainKernel(std::string name, const Platform& platform, OpenCLContext& cl) : NoseHooverChainKernel(name, platform), cl(cl) {
-    }
-    ~OpenCLNoseHooverChainKernel() {}
-    /**
-     * Initialize the kernel.
-     */
-    void initialize();
-    /**
-     * Execute the kernel that propagates the Nose Hoover chain and determines the velocity scale factor.
-     * 
-     * @param context  the context in which to execute this kernel
-     * @param noseHooverChain the object describing the chain to be propagated.
-     * @param kineticEnergies the {absolute, relative} kineticEnergy of the particles being thermostated by this chain.
-     * @param timeStep the time step used by the integrator.
-     * @return the {absolute, relative} velocity scale factor to apply to the particles associated with this heat bath.
-     */
-    std::pair<double, double> propagateChain(ContextImpl& context, const NoseHooverChain &nhc, std::pair<double, double> kineticEnergies, double timeStep);
-    /**
-     * Execute the kernal that computes the total (kinetic + potential) heat bath energy.
-     *
-     * @param context the context in which to execute this kernel
-     * @param noseHooverChain the chain whose energy is to be determined.
-     * @return the total heat bath energy.
-     */
-    double computeHeatBathEnergy(ContextImpl& context, const NoseHooverChain &nhc);
-    /**
-     * Execute the kernel that computes the kinetic energy for a subset of atoms,
-     * or the relative kinetic energy of Drude particles with respect to their parent atoms
-     *
-     * @param context the context in which to execute this kernel
-     * @param noseHooverChain the chain whose energy is to be determined.
-     * @param downloadValue whether the computed value should be downloaded and returned.
-     *
-     */
-    std::pair<double,double> computeMaskedKineticEnergy(ContextImpl& context, const NoseHooverChain &noseHooverChain, bool downloadValue);
-
-    /**
-     * Execute the kernel that scales the velocities of particles associated with a nose hoover chain
-     *
-     * @param context the context in which to execute this kernel
-     * @param noseHooverChain the chain whose energy is to be determined.
-     * @param scaleFactors the {absolute, relative} multiplicative factor by which velocities are scaled.
-     */
-    void scaleVelocities(ContextImpl& context, const NoseHooverChain &noseHooverChain, std::pair<double, double> scaleFactors);
-
-private:
-    int sumWorkGroupSize;
-    OpenCLContext& cl;
-    OpenCLArray energyBuffer, scaleFactorBuffer, kineticEnergyBuffer, chainMasses, chainForces, heatBathEnergy;
-    std::map<int, OpenCLArray> atomlists, pairlists;
-    std::map<int, cl::Kernel> propagateKernels;
-    cl::Kernel reduceEnergyKernel;
-    cl::Kernel computeHeatBathEnergyKernel;
-    cl::Kernel computeAtomsKineticEnergyKernel;
-    cl::Kernel computePairsKineticEnergyKernel;
-    cl::Kernel scaleAtomsVelocitiesKernel;
-    cl::Kernel scalePairsVelocitiesKernel;
-};
-
 /**
  * This kernel is invoked by MonteCarloBarostat to adjust the periodic box volume
  */

platforms/opencl/src/OpenCLKernelFactory.cpp

@@ -132,9 +132,9 @@ KernelImpl* OpenCLKernelFactory::createKernelImpl(std::string name, const Platfo
     if (name == ApplyAndersenThermostatKernel::Name())
         return new CommonApplyAndersenThermostatKernel(name, platform, cl);
     if (name == NoseHooverChainKernel::Name())
-        return new OpenCLNoseHooverChainKernel(name, platform, cl);
+        return new CommonNoseHooverChainKernel(name, platform, cl);
     if (name == IntegrateVelocityVerletStepKernel::Name())
-        return new OpenCLIntegrateVelocityVerletStepKernel(name, platform, cl);
+        return new CommonIntegrateVelocityVerletStepKernel(name, platform, cl);
     if (name == ApplyMonteCarloBarostatKernel::Name())
         return new OpenCLApplyMonteCarloBarostatKernel(name, platform, cl);
     if (name == RemoveCMMotionKernel::Name())

platforms/opencl/src/OpenCLKernels.cpp

@@ -1667,151 +1667,6 @@ void OpenCLCalcNonbondedForceKernel::getLJPMEParameters(double& alpha, int& nx,
     }
 }
 
-void OpenCLIntegrateVelocityVerletStepKernel::initialize(const System& system, const NoseHooverIntegrator& integrator) {
-    cl.getPlatformData().initializeContexts(system);
-    map<string, string> defines;
-    defines["BOLTZ"] = cl.doubleToString(BOLTZ);
-    cl::Program program = cl.createProgram(OpenCLKernelSources::velocityVerlet, defines, "");
-    kernel1 = cl::Kernel(program, "integrateVelocityVerletPart1");
-    kernel2 = cl::Kernel(program, "integrateVelocityVerletPart2");
-    kernel3 = cl::Kernel(program, "integrateVelocityVerletPart3");
-    kernelHardWall = cl::Kernel(program, "integrateVelocityVerletHardWall");
-    prevMaxPairDistance = (cl_float) -1.0;
-    maxPairDistanceBuffer.initialize<cl_float>(cl, 1, "maxPairDistanceBuffer");
-}
-
-void OpenCLIntegrateVelocityVerletStepKernel::execute(ContextImpl& context, const NoseHooverIntegrator& integrator, bool &forcesAreValid) {
-    OpenCLIntegrationUtilities& integration = cl.getIntegrationUtilities();
-    int paddedNumAtoms = cl.getPaddedNumAtoms();
-    double dt = integrator.getStepSize();
-    cl.getIntegrationUtilities().setNextStepSize(dt);
-
-    if (!forcesAreValid) context.calcForcesAndEnergy(true, false);
-
-    const auto& atomList = integrator.getAllThermostatedIndividualParticles();
-    const auto& pairList = integrator.getAllThermostatedPairs();
-    int numAtoms = atomList.size();
-    int numPairs = pairList.size();
-    int numParticles = numAtoms + 2*numPairs;
-    float maxPairDistance = integrator.getMaximumPairDistance();
-    // Make sure atom and pair metadata is uploaded and has the correct dimensions
-    if (prevMaxPairDistance != maxPairDistance) {
-        std::vector<float> tmp(1, maxPairDistance);
-        maxPairDistanceBuffer.upload(tmp);
-        prevMaxPairDistance = maxPairDistance;
-    }
-    if (numAtoms !=0 && (!atomListBuffer.isInitialized() || atomListBuffer.getSize() != numAtoms)) {
-        if (atomListBuffer.isInitialized())
-            atomListBuffer.resize(atomList.size());
-        else
-            atomListBuffer.initialize<cl_int>(cl, atomList.size(), "atomListBuffer");
-        atomListBuffer.upload(atomList);
-    }
-    if (numPairs !=0 && (!pairListBuffer.isInitialized() || pairListBuffer.getSize() != numPairs)) {
-        if (pairListBuffer.isInitialized()) {
-            pairListBuffer.resize(pairList.size());
-            pairTemperatureBuffer.resize(pairList.size());
-        }
-        else {
-            pairListBuffer.initialize<mm_int2>(cl, pairList.size(), "pairListBuffer");
-            pairTemperatureBuffer.initialize<cl_float>(cl, pairList.size(), "pairTemperatureBuffer");
-        }
-        std::vector<mm_int2> tmp;
-        std::vector<float> tmp2;
-        for(const auto &pair : pairList) {
-            tmp.push_back(mm_int2(std::get<0>(pair), std::get<1>(pair)));
-            tmp2.push_back(std::get<2>(pair));
-        }
-        pairListBuffer.upload(tmp);
-        pairTemperatureBuffer.upload(tmp2);
-    }
-
-//// Call the first integration kernel.
-    kernel1.setArg<cl_int>(0, numAtoms);
-    kernel1.setArg<cl_int>(1, numPairs);
-    kernel1.setArg<cl_int>(2, paddedNumAtoms);
-    kernel1.setArg<cl::Buffer>(3, cl.getIntegrationUtilities().getStepSize().getDeviceBuffer());
-    kernel1.setArg<cl::Buffer>(4, cl.getPosq().getDeviceBuffer());
-    setPosqCorrectionArg(cl, kernel1, 5);
-    kernel1.setArg<cl::Buffer>(6, cl.getVelm().getDeviceBuffer());
-    kernel1.setArg<cl::Buffer>(7, cl.getForce().getDeviceBuffer());
-    kernel1.setArg<cl::Buffer>(8, integration.getPosDelta().getDeviceBuffer());
-    if (numAtoms > 0)
-        kernel1.setArg<cl::Buffer>(9, atomListBuffer.getDeviceBuffer());
-    else
-        kernel1.setArg<void*>(9, NULL);
-    if (numPairs > 0)
-        kernel1.setArg<cl::Buffer>(10, pairListBuffer.getDeviceBuffer());
-    else
-        kernel1.setArg<void*>(10, NULL);
-    cl.executeKernel(kernel1, std::max(numAtoms, numPairs));
-
-    //// Apply constraints.
-
-    integration.applyConstraints(integrator.getConstraintTolerance());
-
-    //// Call the second integration kernel.
-    kernel2.setArg<cl_int>(0, numParticles);
-    kernel2.setArg<cl::Buffer>(1, cl.getIntegrationUtilities().getStepSize().getDeviceBuffer());
-    kernel2.setArg<cl::Buffer>(2, cl.getPosq().getDeviceBuffer());
-    setPosqCorrectionArg(cl, kernel2, 3);
-    kernel2.setArg<cl::Buffer>(4, cl.getVelm().getDeviceBuffer());
-    kernel2.setArg<cl::Buffer>(5, integration.getPosDelta().getDeviceBuffer());
-    cl.executeKernel(kernel2, numParticles);
-
-    if (numPairs > 0) {
-        //// Enforce hard wall constraint
-        kernelHardWall.setArg<cl_int>(0, numPairs);
-        kernelHardWall.setArg<cl::Buffer>(1, maxPairDistanceBuffer.getDeviceBuffer());
-        kernelHardWall.setArg<cl::Buffer>(2, cl.getIntegrationUtilities().getStepSize().getDeviceBuffer());
-        kernelHardWall.setArg<cl::Buffer>(3, cl.getPosq().getDeviceBuffer());
-        setPosqCorrectionArg(cl, kernelHardWall, 4);
-        kernelHardWall.setArg<cl::Buffer>(5, cl.getVelm().getDeviceBuffer());
-        kernelHardWall.setArg<cl::Buffer>(6, pairListBuffer.getDeviceBuffer());
-        kernelHardWall.setArg<cl::Buffer>(7, pairTemperatureBuffer.getDeviceBuffer());
-        cl.executeKernel(kernelHardWall, numPairs);
-    }
-
-
-    integration.computeVirtualSites();
-
-    //// Update forces
-    context.calcForcesAndEnergy(true, false);
-    forcesAreValid = true;
-
-    //// Call the third integration kernel.
-    kernel3.setArg<cl_int>(0, numAtoms);
-    kernel3.setArg<cl_int>(1, numPairs);
-    kernel3.setArg<cl_int>(2, paddedNumAtoms);
-    kernel3.setArg<cl::Buffer>(3, cl.getIntegrationUtilities().getStepSize().getDeviceBuffer());
-    kernel3.setArg<cl::Buffer>(4, cl.getPosq().getDeviceBuffer());
-    setPosqCorrectionArg(cl, kernel3, 5);
-    kernel3.setArg<cl::Buffer>(6, cl.getVelm().getDeviceBuffer());
-    kernel3.setArg<cl::Buffer>(7, cl.getForce().getDeviceBuffer());
-    kernel3.setArg<cl::Buffer>(8, integration.getPosDelta().getDeviceBuffer());
-    if (numAtoms > 0)
-        kernel3.setArg<cl::Buffer>(9, atomListBuffer.getDeviceBuffer());
-    else
-        kernel3.setArg<void*>(9, NULL);
-    if (numPairs > 0)
-        kernel3.setArg<cl::Buffer>(10, pairListBuffer.getDeviceBuffer());
-    else
-        kernel3.setArg<void*>(10, NULL);
-    cl.executeKernel(kernel3, std::max(numAtoms, numPairs));
-
-    integration.applyVelocityConstraints(integrator.getConstraintTolerance());
-
-    //// Update the time and step count.
-
-    cl.setTime(cl.getTime()+dt);
-    cl.setStepCount(cl.getStepCount()+1);
-    cl.reorderAtoms();
-}
-
-double OpenCLIntegrateVelocityVerletStepKernel::computeKineticEnergy(ContextImpl& context, const NoseHooverIntegrator& integrator) {
-    return cl.getIntegrationUtilities().computeKineticEnergy(0);
-}
-
 class OpenCLCalcCustomCVForceKernel::ForceInfo : public OpenCLForceInfo {
 public:
     ForceInfo(ComputeForceInfo& force) : OpenCLForceInfo(0), force(force) {
@@ -2037,390 +1892,6 @@ void OpenCLCalcCustomCVForceKernel::copyParametersToContext(ContextImpl& context
         delete function.second;
 }
 
-void OpenCLNoseHooverChainKernel::initialize() {
-    bool useDouble = cl.getUseDoublePrecision() || cl.getUseMixedPrecision();
-    map<string, string> defines;
-    defines["BEGIN_YS_LOOP"] = "const real arr[1] = {1.0}; for(int i=0;i<1;++i) { const real ys = arr[i];";
-    defines["END_YS_LOOP"] = "}";
-    cl::Program program = cl.createProgram(OpenCLKernelSources::noseHooverChain, defines);
-    propagateKernels[1] = cl::Kernel(program, "propagateNoseHooverChain");
-    defines["BEGIN_YS_LOOP"] = "const real arr[3] = {0.828981543588751, -0.657963087177502, 0.828981543588751}; for(int i=0;i<3;++i) { const real ys = arr[i];";
-    program = cl.createProgram(OpenCLKernelSources::noseHooverChain, defines);
-    propagateKernels[3] = cl::Kernel(program, "propagateNoseHooverChain");
-    defines["BEGIN_YS_LOOP"] = "const real arr[5] = {0.2967324292201065, 0.2967324292201065, -0.186929716880426, 0.2967324292201065, 0.2967324292201065}; for(int i=0;i<5;++i) { const real ys = arr[i];";
-    program = cl.createProgram(OpenCLKernelSources::noseHooverChain, defines);
-    propagateKernels[5] = cl::Kernel(program, "propagateNoseHooverChain");
-    program = cl.createProgram(OpenCLKernelSources::noseHooverChain, defines);
-    reduceEnergyKernel = cl::Kernel(program, "reduceEnergyPair");
-
-    computeHeatBathEnergyKernel = cl::Kernel(program, "computeHeatBathEnergy");
-    computeAtomsKineticEnergyKernel = cl::Kernel(program, "computeAtomsKineticEnergy");
-    computePairsKineticEnergyKernel = cl::Kernel(program, "computePairsKineticEnergy");
-    scaleAtomsVelocitiesKernel = cl::Kernel(program, "scaleAtomsVelocities");
-    scalePairsVelocitiesKernel = cl::Kernel(program, "scalePairsVelocities");
-    int energyBufferSize = cl.getEnergyBuffer().getSize();
-    if (cl.getUseDoublePrecision() || cl.getUseMixedPrecision())
-        energyBuffer.initialize<mm_double2>(cl, energyBufferSize, "energyBuffer");
-    else
-        energyBuffer.initialize<mm_float2>(cl, energyBufferSize, "energyBuffer");
-}
-
-std::pair<double, double> OpenCLNoseHooverChainKernel::propagateChain(ContextImpl& context, const NoseHooverChain &nhc, std::pair<double, double> kineticEnergies, double timeStep) {
-    bool useDouble = cl.getUseDoublePrecision() || cl.getUseMixedPrecision();
-    int chainID = nhc.getChainID();
-    int nAtoms = nhc.getThermostatedAtoms().size();
-    int nPairs = nhc.getThermostatedPairs().size();
-    int chainLength = nhc.getChainLength();
-    int numYS = nhc.getNumYoshidaSuzukiTimeSteps();
-    int numMTS = nhc.getNumMultiTimeSteps();
-    int numDOFs = nhc.getNumDegreesOfFreedom();
-    double temperature = nhc.getTemperature();
-    double frequency = nhc.getCollisionFrequency();
-    double relativeTemperature = nhc.getRelativeTemperature();
-    double relativeFrequency = nhc.getRelativeCollisionFrequency();
-
-    if (numYS != 1 && numYS != 3 && numYS != 5) {
-        throw OpenMMException("Number of Yoshida Suzuki time steps has to be 1, 3, or 5.");
-    }
-
-    auto & chainState = cl.getIntegrationUtilities().getNoseHooverChainState();
-
-    if (!scaleFactorBuffer.isInitialized() || scaleFactorBuffer.getSize() == 0) {
-        if (useDouble) {
-            std::vector<mm_double2> zeros{{0,0}};
-            if (scaleFactorBuffer.isInitialized())
-                scaleFactorBuffer.resize(1);
-            else
-                scaleFactorBuffer.initialize<mm_double2>(cl, 1, "scaleFactorBuffer");
-            scaleFactorBuffer.upload(zeros);
-        }
-        else {
-            std::vector<mm_float2> zeros{{0,0}};
-            if (scaleFactorBuffer.isInitialized())
-                scaleFactorBuffer.resize(1);
-            else
-                scaleFactorBuffer.initialize<mm_float2>(cl, 1, "scaleFactorBuffer");
-            scaleFactorBuffer.upload(zeros);
-        }
-    }
-    if (!chainForces.isInitialized() || !chainMasses.isInitialized()) {
-        if (useDouble) {
-            std::vector<cl_double> zeros(chainLength,0);
-            if (chainForces.isInitialized()) {
-                chainMasses.resize(chainLength);
-                chainForces.resize(chainLength);
-            }
-            else {
-                chainMasses.initialize<cl_double>(cl, chainLength, "chainMasses");
-                chainForces.initialize<cl_double>(cl, chainLength, "chainForces");
-            }
-            chainMasses.upload(zeros);
-            chainForces.upload(zeros);
-        }
-        else {
-            std::vector<cl_float> zeros(chainLength,0);
-            if (chainForces.isInitialized()) {
-                chainMasses.resize(chainLength);
-                chainForces.resize(chainLength);
-            }
-            else {
-                chainMasses.initialize<cl_float>(cl, chainLength, "chainMasses");
-                chainForces.initialize<cl_float>(cl, chainLength, "chainForces");
-            }
-            chainMasses.upload(zeros);
-            chainForces.upload(zeros);
-        }
-    }
-    if (chainForces.getSize() < chainLength)
-        chainMasses.resize(chainLength);
-    if (chainMasses.getSize() < chainLength)
-        chainMasses.resize(chainLength);
-
-    float timeStepFloat = (float) timeStep;
-    // N.B. We ignore the incoming kineticEnergy and grab it from the device buffer instead
-    if (nAtoms) {
-        if (!chainState.count(2*chainID))
-            chainState[2*chainID] = ComputeArray();
-        if (!chainState.at(2*chainID).isInitialized() || chainState.at(2*chainID).getSize() != chainLength) {
-            // We need to upload the OpenCL array
-            if (useDouble) {
-                if (chainState.at(2*chainID).isInitialized())
-                    chainState.at(2*chainID).resize(chainLength);
-                else
-                    chainState.at(2*chainID).initialize<mm_double2>(cl, chainLength, "chainState" + std::to_string(2*chainID));
-                std::vector<mm_double2> zeros(chainLength, mm_double2(0.0, 0.0));
-                chainState.at(2*chainID).upload(zeros.data());
-            }
-            else {
-                if (chainState.at(2*chainID).isInitialized())
-                    chainState.at(2*chainID).resize(chainLength);
-                else
-                    chainState.at(2*chainID).initialize<mm_float2>(cl, chainLength, "chainState" + std::to_string(2*chainID));
-                std::vector<mm_float2> zeros(chainLength, mm_float2(0.0f, 0.0f));
-                chainState.at(2*chainID).upload(zeros.data());
-            }
-        }
-        int chainType = 0;
-        double kT = BOLTZ * temperature;
-        float kTfloat = (float) kT;
-        float frequencyFloat = (float) frequency;
-        propagateKernels[numYS].setArg<cl::Buffer>(0, cl.unwrap(chainState[2*chainID]).getDeviceBuffer());
-        propagateKernels[numYS].setArg<cl::Buffer>(1, kineticEnergyBuffer.getDeviceBuffer());
-        propagateKernels[numYS].setArg<cl::Buffer>(2, scaleFactorBuffer.getDeviceBuffer());
-        propagateKernels[numYS].setArg<cl::Buffer>(3, chainMasses.getDeviceBuffer());
-        propagateKernels[numYS].setArg<cl::Buffer>(4, chainForces.getDeviceBuffer());
-        propagateKernels[numYS].setArg<cl_int>(5, chainType);
-        propagateKernels[numYS].setArg<cl_int>(6, chainLength);
-        propagateKernels[numYS].setArg<cl_int>(7, numMTS);
-        propagateKernels[numYS].setArg<cl_int>(8, numDOFs);
-        propagateKernels[numYS].setArg<cl_float>(9, timeStepFloat);
-        if (useDouble) 
-            propagateKernels[numYS].setArg<cl_double>(10, kT);
-        else
-            propagateKernels[numYS].setArg<cl_float>(10, kTfloat);
-        propagateKernels[numYS].setArg<cl_float>(11, frequencyFloat);
-        cl.executeKernel(propagateKernels[numYS], 1, 1);
-    }
-    if (nPairs) {
-        if (!chainState.count(2*chainID+1))
-            chainState[2*chainID+1] = ComputeArray();
-        if (!chainState.at(2*chainID+1).isInitialized() || chainState.at(2*chainID+1).getSize() != chainLength) {
-            // We need to upload the OpenCL array
-            if (useDouble) {
-                if (chainState.at(2*chainID+1).isInitialized())
-                    chainState.at(2*chainID+1).resize(chainLength);
-                else
-                    chainState.at(2*chainID+1).initialize<mm_double2>(cl, chainLength, "chainState" + std::to_string(2*chainID+1));
-                std::vector<mm_double2> zeros(chainLength, mm_double2(0.0, 0.0));
-                chainState.at(2*chainID+1).upload(zeros.data());
-            }
-            else {
-                if (chainState.at(2*chainID+1).isInitialized())
-                    chainState.at(2*chainID+1).resize(chainLength);
-                else
-                    chainState.at(2*chainID+1).initialize<mm_float2>(cl, chainLength, "chainState" + std::to_string(2*chainID+1));
-                std::vector<mm_float2> zeros(chainLength, mm_float2(0.0f, 0.0f));
-                chainState.at(2*chainID+1).upload(zeros.data());
-            }
-        }
-        int chainType = 1;
-        double kT = BOLTZ * relativeTemperature;
-        int ndf = 3*nPairs;
-        float kTfloat = (float) kT;
-        float frequencyFloat = (float) relativeFrequency;
-        propagateKernels[numYS].setArg<cl::Buffer>(0, cl.unwrap(chainState[2*chainID+1]).getDeviceBuffer());
-        propagateKernels[numYS].setArg<cl::Buffer>(1, kineticEnergyBuffer.getDeviceBuffer());
-        propagateKernels[numYS].setArg<cl::Buffer>(2, scaleFactorBuffer.getDeviceBuffer());
-        propagateKernels[numYS].setArg<cl::Buffer>(3, chainMasses.getDeviceBuffer());
-        propagateKernels[numYS].setArg<cl::Buffer>(4, chainForces.getDeviceBuffer());
-        propagateKernels[numYS].setArg<cl_int>(5, chainType);
-        propagateKernels[numYS].setArg<cl_int>(6, chainLength);
-        propagateKernels[numYS].setArg<cl_int>(7, numMTS);
-        propagateKernels[numYS].setArg<cl_int>(8, ndf);
-        propagateKernels[numYS].setArg<cl_float>(9, timeStepFloat);
-        if (useDouble) 
-            propagateKernels[numYS].setArg<cl_double>(10, kT);
-        else
-            propagateKernels[numYS].setArg<cl_float>(10, kTfloat);
-        propagateKernels[numYS].setArg<cl_float>(11, frequencyFloat);
-        cl.executeKernel(propagateKernels[numYS], 1, 1);
-    }
-    return {0, 0};
-}
-
-double OpenCLNoseHooverChainKernel::computeHeatBathEnergy(ContextImpl& context, const NoseHooverChain &nhc) {
-
-    bool useDouble = cl.getUseDoublePrecision() || cl.getUseMixedPrecision();
-
-    int chainID = nhc.getChainID();
-    int chainLength = nhc.getChainLength();
-
-    auto & chainState = cl.getIntegrationUtilities().getNoseHooverChainState();
-
-    bool absChainIsValid = chainState.count(2*chainID) != 0 &&
-                           chainState[2*chainID].isInitialized() &&
-                           chainState[2*chainID].getSize() == chainLength;
-    bool relChainIsValid = chainState.count(2*chainID+1) != 0 &&
-                           chainState[2*chainID+1].isInitialized() &&
-                           chainState[2*chainID+1].getSize() == chainLength;
-
-    if (!absChainIsValid && !relChainIsValid) return 0.0;
-
-    if (!heatBathEnergy.isInitialized() || heatBathEnergy.getSize() == 0) {
-        if (useDouble) {
-            std::vector<cl_double> one(1);
-            heatBathEnergy.initialize<cl_double>(cl, 1, "heatBathEnergy");
-            heatBathEnergy.upload(one);
-        }
-        else {
-            std::vector<cl_float> one(1);
-            heatBathEnergy.initialize<cl_float>(cl, 1, "heatBathEnergy");
-            heatBathEnergy.upload(one);
-        }
-    }
-
-    cl.clearBuffer(heatBathEnergy);
-
-    if (absChainIsValid) {
-        int numDOFs = nhc.getNumDegreesOfFreedom();
-        double temperature = nhc.getTemperature();
-        double frequency = nhc.getCollisionFrequency();
-        double kT = BOLTZ * temperature;
-        float kTfloat = (float) kT;
-        float frequencyFloat = (float) frequency;
-
-        computeHeatBathEnergyKernel.setArg<cl::Buffer>(0, heatBathEnergy.getDeviceBuffer());
-        computeHeatBathEnergyKernel.setArg<cl_int>(1, chainLength);
-        computeHeatBathEnergyKernel.setArg<cl_int>(2, numDOFs); 
-        if (useDouble)
-            computeHeatBathEnergyKernel.setArg<cl_double>(3, kT);
-        else
-            computeHeatBathEnergyKernel.setArg<cl_float>(3, kTfloat);
-        computeHeatBathEnergyKernel.setArg<cl_float>(4, frequencyFloat);
-        computeHeatBathEnergyKernel.setArg<cl::Buffer>(5, cl.unwrap(chainState[2*chainID]).getDeviceBuffer());
-        cl.executeKernel(computeHeatBathEnergyKernel, 1, 1);
-    }
-    if (relChainIsValid) {
-        int numDOFs = 3 * nhc.getThermostatedPairs().size();
-        double temperature = nhc.getRelativeTemperature();
-        double frequency = nhc.getRelativeCollisionFrequency();
-        double kT = BOLTZ * temperature;
-        float kTfloat = (float) kT;
-        float frequencyFloat = (float) frequency;
-
-        computeHeatBathEnergyKernel.setArg<cl::Buffer>(0, heatBathEnergy.getDeviceBuffer());
-        computeHeatBathEnergyKernel.setArg<cl_int>(1, chainLength);
-        computeHeatBathEnergyKernel.setArg<cl_int>(2, numDOFs); 
-        if (useDouble)
-            computeHeatBathEnergyKernel.setArg<cl_double>(3, kT);
-        else
-            computeHeatBathEnergyKernel.setArg<cl_float>(3, kTfloat);
-        computeHeatBathEnergyKernel.setArg<cl_float>(4, frequencyFloat);
-        computeHeatBathEnergyKernel.setArg<cl::Buffer>(5, cl.unwrap(chainState[2*chainID+1]).getDeviceBuffer());
-        cl.executeKernel(computeHeatBathEnergyKernel, 1, 1);
-    }
-
-
-    void * pinnedBuffer = cl.getPinnedBuffer();
-    heatBathEnergy.download(pinnedBuffer);
-    if (useDouble)
-        return *((double*) pinnedBuffer);
-    else
-        return *((float*) pinnedBuffer);
-}
-
-std::pair<double, double> OpenCLNoseHooverChainKernel::computeMaskedKineticEnergy(ContextImpl& context, const NoseHooverChain &nhc, bool downloadValue) {
-
-    bool useDouble = cl.getUseDoublePrecision() || cl.getUseMixedPrecision();
-
-    int chainID = nhc.getChainID();
-    const auto & nhcAtoms = nhc.getThermostatedAtoms();
-    const auto & nhcPairs = nhc.getThermostatedPairs();
-    auto nAtoms = nhcAtoms.size();
-    auto nPairs = nhcPairs.size();
-    if (nAtoms) {
-        if (!atomlists.count(chainID)) { 
-            // We need to upload the OpenCL array
-            atomlists[chainID] = OpenCLArray();
-            atomlists[chainID].initialize<int>(cl, nAtoms, "atomlist" + std::to_string(chainID));
-            atomlists[chainID].upload(nhcAtoms);
-        }
-        if (atomlists[chainID].getSize() != nAtoms) {
-            throw OpenMMException("Number of atoms changed. Cannot be handled by the same Nose-Hoover thermostat.");
-        }
-    }
-    if (nPairs) {
-        if (!pairlists.count(chainID)) { 
-            // We need to upload the OpenCL array
-            pairlists[chainID] = OpenCLArray();
-            pairlists[chainID].initialize<mm_int2>(cl, nPairs, "pairlist" + std::to_string(chainID));
-            std::vector<mm_int2> int2vec;
-            for(const auto &p : nhcPairs) int2vec.push_back(mm_int2(p.first, p.second));
-            pairlists[chainID].upload(int2vec);
-        }
-        if (pairlists[chainID].getSize() != nPairs) {
-            throw OpenMMException("Number of thermostated pairs changed. Cannot be handled by the same Nose-Hoover thermostat.");
-        }
-    }
-    if (!kineticEnergyBuffer.isInitialized() || kineticEnergyBuffer.getSize() == 0) {
-        if (useDouble) {
-            std::vector<mm_double2> zeros{{0,0}};
-            kineticEnergyBuffer.initialize<mm_double2>(cl, 1, "kineticEnergyBuffer");
-            kineticEnergyBuffer.upload(zeros);
-        }
-        else {
-            std::vector<mm_float2> zeros{{0,0}};
-            kineticEnergyBuffer.initialize<mm_float2>(cl, 1, "kineticEnergyBuffer");
-            kineticEnergyBuffer.upload(zeros);
-        }
-    }
-    cl.clearBuffer(cl.getEnergyBuffer());
-    if (nAtoms) {
-        computeAtomsKineticEnergyKernel.setArg<cl::Buffer>(0, energyBuffer.getDeviceBuffer());
-        computeAtomsKineticEnergyKernel.setArg<cl_int>(1, nAtoms);
-        computeAtomsKineticEnergyKernel.setArg<cl::Buffer>(2, cl.getVelm().getDeviceBuffer());
-        computeAtomsKineticEnergyKernel.setArg<cl::Buffer>(3, atomlists[chainID].getDeviceBuffer());
-        cl.executeKernel(computeAtomsKineticEnergyKernel, nAtoms);
-    }
-    if (nPairs) {
-        computePairsKineticEnergyKernel.setArg<cl::Buffer>(0, energyBuffer.getDeviceBuffer());
-        computePairsKineticEnergyKernel.setArg<cl_int>(1, nPairs);
-        computePairsKineticEnergyKernel.setArg<cl::Buffer>(2, cl.getVelm().getDeviceBuffer());
-        computePairsKineticEnergyKernel.setArg<cl::Buffer>(3, pairlists[chainID].getDeviceBuffer());
-        cl.executeKernel(computePairsKineticEnergyKernel, nPairs);
-    }
-    int bufferSize = energyBuffer.getSize();
-    int workGroupSize  = cl.getDevice().getInfo<CL_DEVICE_MAX_WORK_GROUP_SIZE>();
-    if (workGroupSize > 512)
-        workGroupSize = 512;
-    reduceEnergyKernel.setArg<cl::Buffer>(0, energyBuffer.getDeviceBuffer());
-    reduceEnergyKernel.setArg<cl::Buffer>(1, kineticEnergyBuffer.getDeviceBuffer());
-    reduceEnergyKernel.setArg<cl_int>(2, bufferSize);
-    reduceEnergyKernel.setArg<cl_int>(3, workGroupSize);
-    reduceEnergyKernel.setArg(4, workGroupSize*energyBuffer.getElementSize(), NULL);
-    cl.executeKernel(reduceEnergyKernel, workGroupSize, workGroupSize);
-
-    std::pair<double, double> KEs = {0, 0};
-    if (downloadValue) {
-        if (useDouble) {
-            mm_double2 tmp;
-            kineticEnergyBuffer.download(&tmp);
-            KEs.first = tmp.x;
-            KEs.second = tmp.y;
-        }
-        else {
-            mm_float2 tmp;
-            kineticEnergyBuffer.download(&tmp);
-            KEs.first = tmp.x;
-            KEs.second = tmp.y;
-        }
-    }
-    return KEs;
-}
-
-void OpenCLNoseHooverChainKernel::scaleVelocities(ContextImpl& context, const NoseHooverChain &nhc, std::pair<double, double> scaleFactor) {
-    // For now we assume that the atoms and pairs info is valid, because compute{Atoms|Pairs}KineticEnergy must have been
-    // called before this kernel.  If that ever ceases to be true, some sanity checks are needed here.
-
-    int chainID = nhc.getChainID();
-    auto nAtoms = nhc.getThermostatedAtoms().size();
-    auto nPairs = nhc.getThermostatedPairs().size();
-    if (nAtoms) {
-        scaleAtomsVelocitiesKernel.setArg<cl::Buffer>(0, scaleFactorBuffer.getDeviceBuffer());
-        scaleAtomsVelocitiesKernel.setArg<cl_int>(1, nAtoms);
-        scaleAtomsVelocitiesKernel.setArg<cl::Buffer>(2, cl.getVelm().getDeviceBuffer());
-        scaleAtomsVelocitiesKernel.setArg<cl::Buffer>(3, atomlists[chainID].getDeviceBuffer());
-        cl.executeKernel(scaleAtomsVelocitiesKernel, nAtoms);
-    }
-    if (nPairs) {
-        scalePairsVelocitiesKernel.setArg<cl::Buffer>(0, scaleFactorBuffer.getDeviceBuffer());
-        scalePairsVelocitiesKernel.setArg<cl_int>(1, nPairs);
-        scalePairsVelocitiesKernel.setArg<cl::Buffer>(2, cl.getVelm().getDeviceBuffer());
-        scalePairsVelocitiesKernel.setArg<cl::Buffer>(3, pairlists[chainID].getDeviceBuffer());
-        cl.executeKernel(scalePairsVelocitiesKernel, nPairs);
-    }
-}
-
 void OpenCLApplyMonteCarloBarostatKernel::initialize(const System& system, const Force& thermostat) {
     savedPositions.initialize(cl, cl.getPaddedNumAtoms(), cl.getUseDoublePrecision() ? sizeof(mm_double4) : sizeof(mm_float4), "savedPositions");
     savedForces.initialize(cl, cl.getPaddedNumAtoms(), cl.getUseDoublePrecision() ? sizeof(mm_double4) : sizeof(mm_float4), "savedForces");

platforms/opencl/src/kernels/velocityVerlet.cl

-/**
- * Perform the first step of Velocity Verlet integration.
- */
-
-__kernel void integrateVelocityVerletPart1(int numAtoms, int numPairs, int paddedNumAtoms, __global const mixed2* restrict dt, __global const real4* restrict posq,
-        __global const real4* restrict posqCorrection, __global mixed4* restrict velm, __global const real4* restrict force, __global mixed4* restrict posDelta,
-        __global const int* restrict atomList, __global const int2* restrict pairList) {
-    const mixed2 stepSize = dt[0];
-    const mixed dtPos = stepSize.y;
-    const mixed dtVel = 0.5f*(stepSize.x+stepSize.y);
-    int index = get_global_id(0);
-    while (index < numAtoms) {
-        int atom = atomList[index];
-        mixed4 velocity = velm[atom];
-        if (velocity.w != 0.0) {
-#ifdef USE_MIXED_PRECISION
-            real4 pos1 = posq[atom];
-            real4 pos2 = posqCorrection[atom];
-            mixed4 pos = (mixed4) (pos1.x+(mixed)pos2.x, pos1.y+(mixed)pos2.y, pos1.z+(mixed)pos2.z, pos1.w);
-#else
-            real4 pos = posq[atom];
-#endif
-            velocity.x += 0.5f * dtVel*force[atom].x*velocity.w;
-            velocity.y += 0.5f * dtVel*force[atom].y*velocity.w;
-            velocity.z += 0.5f * dtVel*force[atom].z*velocity.w;
-            pos.x = velocity.x*dtPos;
-            pos.y = velocity.y*dtPos;
-            pos.z = velocity.z*dtPos;
-            posDelta[atom] = pos;
-            velm[atom] = velocity;
-        }
-        index += get_global_size(0);
-    }
-    index = get_global_id(0);
-    while (index < numPairs){
-        int atom1 = pairList[index].x;
-        int atom2 = pairList[index].y;
-        mixed4 v1 = velm[atom1];
-        mixed4 v2 = velm[atom2];
-        mixed m1 = v1.w == 0.0f ? 0.0f : 1.0f / v1.w;
-        mixed m2 = v2.w == 0.0f ? 0.0f : 1.0f / v2.w;
-        mixed mass1fract = m1 / (m1 + m2);
-        mixed mass2fract = m2 / (m1 + m2);
-        mixed invRedMass = (m1 * m2 != 0.0f) ? (m1 + m2)/(m1 * m2) : 0.0f;
-        mixed invTotMass = (m1 + m2 != 0.0f) ? 1.0f /(m1 + m2) : 0.0f;
-        mixed3 comVel;
-        comVel.x= v1.x*mass1fract + v2.x*mass2fract;
-        comVel.y= v1.y*mass1fract + v2.y*mass2fract;
-        comVel.z= v1.z*mass1fract + v2.z*mass2fract;
-        mixed3 relVel;
-        relVel.x= v2.x - v1.x;
-        relVel.y= v2.y - v1.y;
-        relVel.z= v2.z - v1.z;
-
-        mixed3 comFrc;
-        comFrc.x = force[atom1].x + force[atom2].x;
-        comFrc.y = force[atom1].y + force[atom2].y;
-        comFrc.z = force[atom1].z + force[atom2].z;
-        mixed3 relFrc;
-        relFrc.x = mass1fract*force[atom2].x - mass2fract*force[atom1].x;
-        relFrc.y = mass1fract*force[atom2].y - mass2fract*force[atom1].y;
-        relFrc.z = mass1fract*force[atom2].z - mass2fract*force[atom1].z;
-        comVel.x += comFrc.x * 0.5f * dtVel * invTotMass;
-        comVel.y += comFrc.y * 0.5f * dtVel * invTotMass;
-        comVel.z += comFrc.z * 0.5f * dtVel * invTotMass;
-        relVel.x += relFrc.x * 0.5f * dtVel * invRedMass;
-        relVel.y += relFrc.y * 0.5f * dtVel * invRedMass;
-        relVel.z += relFrc.z * 0.5f * dtVel * invRedMass;
-#ifdef USE_MIXED_PRECISION
-        real4 posv1 = posq[atom1];
-        real4 posv2 = posq[atom2];
-        real4 posc1 = posqCorrection[atom1];
-        real4 posc2 = posqCorrection[atom2];
-        mixed4 pos1 = (mixed4) (posv1.x+(mixed)posc1.x, posv1.y+(mixed)posc1.y, posv1.z+(mixed)posc1.z, posv1.w);
-        mixed4 pos2 = (mixed4) (posv2.x+(mixed)posc2.x, posv2.y+(mixed)posc2.y, posv2.z+(mixed)posc2.z, posv2.w);
-#else
-        real4 pos1 = posq[atom1];
-        real4 pos2 = posq[atom2];
-#endif
-        if (v1.w != 0.0f) {
-            v1.x = comVel.x - relVel.x*mass2fract;
-            v1.y = comVel.y - relVel.y*mass2fract;
-            v1.z = comVel.z - relVel.z*mass2fract;
-            pos1.x = v1.x*dtPos;
-            pos1.y = v1.y*dtPos;
-            pos1.z = v1.z*dtPos;
-            posDelta[atom1] = pos1;
-            velm[atom1] = v1;
-        }
-        if (v2.w != 0.0f) {
-            v2.x = comVel.x + relVel.x*mass1fract;
-            v2.y = comVel.y + relVel.y*mass1fract;
-            v2.z = comVel.z + relVel.z*mass1fract;
-            pos2.x = v2.x*dtPos;
-            pos2.y = v2.y*dtPos;
-            pos2.z = v2.z*dtPos;
-            posDelta[atom2] = pos2;
-            velm[atom2] = v2;
-        }
-        index += get_global_size(0);
-     }
-}
-
-/**
- * Perform the second step of Velocity Verlet integration.
- */
-
-__kernel void integrateVelocityVerletPart2(int numAtoms, __global mixed2* restrict dt, __global real4* restrict posq,
-        __global real4* restrict posqCorrection, __global mixed4* restrict velm, __global const mixed4* restrict posDelta) {
-    mixed2 stepSize = dt[0];
-    int index = get_global_id(0);
-    if (index == 0)
-        dt[0].x = stepSize.y;
-    while(index < numAtoms) {
-        mixed4 velocity = velm[index];
-        if (velocity.w != 0.0) {
-#ifdef USE_MIXED_PRECISION
-            real4 pos1 = posq[index];
-            real4 pos2 = posqCorrection[index];
-            mixed4 pos = (mixed4) (pos1.x+(mixed)pos2.x, pos1.y+(mixed)pos2.y, pos1.z+(mixed)pos2.z, pos1.w);
-#else
-            real4 pos = posq[index];
-#endif
-            mixed4 delta = posDelta[index];
-            pos.xyz += delta.xyz;
-#ifdef USE_MIXED_PRECISION
-            posq[index] = (real4) ((real) pos.x, (real) pos.y, (real) pos.z, (real) pos.w);
-            posqCorrection[index] = (real4) (pos.x-(real) pos.x, pos.y-(real) pos.y, pos.z-(real) pos.z, 0);
-#else
-            posq[index] = pos;
-#endif
-        }
-        index += get_global_size(0);
-    }
-}
-
-/**
- * Perform the third step of Velocity Verlet integration.
- */
-
-__kernel void integrateVelocityVerletPart3(int numAtoms, int numPairs, int paddedNumAtoms, __global mixed2* restrict dt, __global real4* restrict posq,
-        __global real4* restrict posqCorrection, __global mixed4* restrict velm, __global const real4* restrict force, __global const mixed4* restrict posDelta,
-        __global const int* restrict atomList, __global const int2* __restrict__ pairList) {
-    mixed2 stepSize = dt[0];
-#ifndef SUPPORTS_DOUBLE_PRECISION
-    double oneOverDt = 1.0/stepSize.y;
-#else
-    float oneOverDt = 1.0f/stepSize.y;
-    float correction = (1.0f-oneOverDt*stepSize.y)/stepSize.y;
-#endif
-    const mixed dtVel = 0.5f*(stepSize.x+stepSize.y);
-    int index = get_global_id(0);
-    if (index == 0)
-        dt[0].x = stepSize.y;
-    while(index < numAtoms) {
-        int atom = atomList[index];
-        mixed4 velocity = velm[atom];
-        if (velocity.w != 0.0) {
-            mixed4 deltaXconstrained = posDelta[atom];
-            velocity.x += 0.5f * dtVel*force[atom].x*velocity.w + (deltaXconstrained.x - velocity.x*stepSize.y)*oneOverDt;
-            velocity.y += 0.5f * dtVel*force[atom].y*velocity.w + (deltaXconstrained.y - velocity.y*stepSize.y)*oneOverDt;
-            velocity.z += 0.5f * dtVel*force[atom].z*velocity.w + (deltaXconstrained.z - velocity.z*stepSize.y)*oneOverDt;
-#ifdef SUPPORTS_DOUBLE_PRECISION
-            velocity.x += (deltaXconstrained.x - velocity.x*stepSize.y)*correction;
-            velocity.y += (deltaXconstrained.y - velocity.y*stepSize.y)*correction;
-            velocity.z += (deltaXconstrained.z - velocity.z*stepSize.y)*correction;
-#endif
-            velm[atom] = velocity;
-        }
-        index += get_global_size(0);
-    }
-    index = get_global_id(0);
-    while(index < numPairs) {
-        int atom1 = pairList[index].x;
-        int atom2 = pairList[index].y;
-        mixed4 v1 = velm[atom1];
-        mixed4 v2 = velm[atom2];
-        mixed m1 = v1.w == 0.0f ? 0.0f : 1.0f / v1.w;
-        mixed m2 = v2.w == 0.0f ? 0.0f : 1.0f / v2.w;
-        mixed mass1fract = m1 / (m1 + m2);
-        mixed mass2fract = m2 / (m1 + m2);
-        mixed invRedMass = (m1 * m2 != 0.0f) ? (m1 + m2)/(m1 * m2) : 0.0f;
-        mixed invTotMass = (m1 + m2 != 0.0f) ? 1.0f /(m1 + m2) : 0.0f;
-        mixed3 comVel;
-        comVel.x= v1.x*mass1fract + v2.x*mass2fract;
-        comVel.y= v1.y*mass1fract + v2.y*mass2fract;
-        comVel.z= v1.z*mass1fract + v2.z*mass2fract;
-        mixed3 relVel;
-        relVel.x= v2.x - v1.x;
-        relVel.y= v2.y - v1.y;
-        relVel.z= v2.z - v1.z;
-
-        mixed3 comFrc;
-        comFrc.x = force[atom1].x + force[atom2].x;
-        comFrc.y = force[atom1].y + force[atom2].y;
-        comFrc.z = force[atom1].z + force[atom2].z;
-        mixed3 relFrc;
-        relFrc.x = mass1fract*force[atom2].x - mass2fract*force[atom1].x;
-        relFrc.y = mass1fract*force[atom2].y - mass2fract*force[atom1].y;
-        relFrc.z = mass1fract*force[atom2].z - mass2fract*force[atom1].z;
-        comVel.x += comFrc.x * 0.5f * dtVel * invTotMass;
-        comVel.y += comFrc.y * 0.5f * dtVel * invTotMass;
-        comVel.z += comFrc.z * 0.5f * dtVel * invTotMass;
-        relVel.x += relFrc.x * 0.5f * dtVel * invRedMass;
-        relVel.y += relFrc.y * 0.5f * dtVel * invRedMass;
-        relVel.z += relFrc.z * 0.5f * dtVel * invRedMass;
-        if (v1.w != 0.0f) {
-            mixed4 deltaXconstrained = posDelta[atom1];
-            v1.x = comVel.x - relVel.x*mass2fract + (deltaXconstrained.x - v1.x*stepSize.y)*oneOverDt;
-            v1.y = comVel.y - relVel.y*mass2fract + (deltaXconstrained.y - v1.y*stepSize.y)*oneOverDt;
-            v1.z = comVel.z - relVel.z*mass2fract + (deltaXconstrained.z - v1.z*stepSize.y)*oneOverDt;
-#ifdef SUPPORTS_DOUBLE_PRECISION
-            v1.x += (deltaXconstrained.x - v1.x*stepSize.y)*correction;
-            v1.y += (deltaXconstrained.y - v1.y*stepSize.y)*correction;
-            v1.z += (deltaXconstrained.z - v1.z*stepSize.y)*correction;
-#endif
-            velm[atom1] = v1;
-        }
-        if (v2.w != 0.0f) {
-            mixed4 deltaXconstrained = posDelta[atom2];
-            v2.x = comVel.x + relVel.x*mass1fract + (deltaXconstrained.x - v2.x*stepSize.y)*oneOverDt;
-            v2.y = comVel.y + relVel.y*mass1fract + (deltaXconstrained.y - v2.y*stepSize.y)*oneOverDt;
-            v2.z = comVel.z + relVel.z*mass1fract + (deltaXconstrained.z - v2.z*stepSize.y)*oneOverDt;
-#ifdef SUPPORTS_DOUBLE_PRECISION
-            v2.x += (deltaXconstrained.x - v2.x*stepSize.y)*correction;
-            v2.y += (deltaXconstrained.y - v2.y*stepSize.y)*correction;
-            v2.z += (deltaXconstrained.z - v2.z*stepSize.y)*correction;
-#endif
-            velm[atom2] = v2;
-        }
-        index += get_global_size(0);
-    }
-}
-
-__kernel void integrateVelocityVerletHardWall(int numPairs, __global const float* restrict maxPairDistance, 
-        __global mixed2* restrict dt, __global real4* restrict posq,
-        __global real4* restrict posqCorrection, __global mixed4* restrict velm, 
-        __global const int2* restrict pairList, __global const float* __restrict__ pairTemperature) {
-
-    mixed dtPos = dt[0].y;
-    mixed maxDelta = (mixed) maxPairDistance[0];
-    if (maxDelta > 0){
-        int index = get_global_id(0);
-        while(index < numPairs) {
-
-            const mixed hardWallScale = sqrt( ((mixed) pairTemperature[index]) * ((mixed) BOLTZ));
-            int2 atom = (int2) (pairList[index].x, pairList[index].y);
-#ifdef USE_MIXED_PRECISION
-            real4 posv1 = posq[atom.x];
-            real4 posc1 = posqCorrection[atom.x];
-            mixed4 pos1 = (mixed4) (posv1.x+(mixed)posc1.x, posv1.y+(mixed)posc1.y, posv1.z+(mixed)posc1.z, posv1.w);
-            real4 posv2 = posq[atom.y];
-            real4 posc2 = posqCorrection[atom.y];
-            mixed4 pos2 = (mixed4) (posv2.x+(mixed)posc2.x, posv2.y+(mixed)posc2.y, posv2.z+(mixed)posc2.z, posv2.w);
-#else
-            real4 pos1 = posq[atom.x];
-            real4 pos2 = posq[atom.y];
-#endif
-            mixed3 delta = (mixed3) (
-                (mixed) (pos1.x - pos2.x),
-                (mixed) (pos1.y - pos2.y),
-                (mixed) (pos1.z - pos2.z)
-            );
-            mixed r = sqrt(delta.x*delta.x + delta.y*delta.y + delta.z*delta.z);
-            mixed rInv = 1/r;
-            if (rInv*maxDelta < 1.0) {
-                // The constraint has been violated, so make the inter-particle distance "bounce"
-                // off the hard wall.
-                mixed3 bondDir = (mixed3) (delta.x * rInv, delta.y * rInv, delta.z * rInv);
-                mixed3 vel1 = (mixed3) (velm[atom.x].x, velm[atom.x].y, velm[atom.x].z);
-                mixed3 vel2 = (mixed3) (velm[atom.y].x, velm[atom.y].y, velm[atom.y].z);
-                mixed m1 = velm[atom.x].w != 0.0 ? 1.0/velm[atom.x].w : 0.0;
-                mixed m2 = velm[atom.y].w != 0.0 ? 1.0/velm[atom.y].w : 0.0;
-                mixed invTotMass = (m1 + m2 != 0.0) ? 1.0 /(m1 + m2) : 0.0;
-                mixed deltaR = r-maxDelta;
-                mixed deltaT = dtPos;
-                mixed dt = dtPos;
-
-                mixed dotvr1 = vel1.x*bondDir.x + vel1.y*bondDir.y + vel1.z*bondDir.z;
-                mixed3 vb1 = (mixed3) (bondDir.x*dotvr1, bondDir.y*dotvr1, bondDir.z*dotvr1);
-                mixed3 vp1 = (mixed3) (vel1.x-vb1.x, vel1.y-vb1.y, vel1.z-vb1.z);
-                if (m2 == 0) {
-                    // The parent particle is massless, so move only the Drude particle.
-
-                    if (dotvr1 != 0.0)
-                        deltaT = deltaR/fabs(dotvr1);
-                    if (deltaT > dtPos)
-                        deltaT = dtPos;
-                    dotvr1 = -dotvr1*hardWallScale/(fabs(dotvr1)*sqrt(m1));
-                    mixed dr = -deltaR + deltaT*dotvr1;
-                    pos1.x += bondDir.x*dr;
-                    pos1.y += bondDir.y*dr;
-                    pos1.z += bondDir.z*dr;
-                    velm[atom.x] = (mixed4) (vp1.x + bondDir.x*dotvr1, vp1.y + bondDir.y*dotvr1, vp1.z + bondDir.z*dotvr1, velm[atom.x].w);
-#ifdef USE_MIXED_PRECISION
-                    posq[atom.x] = (real4) ((real) pos1.x, (real) pos1.y, (real) pos1.z, (real) pos1.w);
-                    posqCorrection[atom.x] = (real4) (pos1.x-(real) pos1.x, pos1.y-(real) pos1.y, pos1.z-(real) pos1.z, 0);
-#else
-                    posq[atom.x] = pos1;
-#endif
-                }
-                else {
-                    // Move both particles.
-                    mixed dotvr2 = vel2.x*bondDir.x + vel2.y*bondDir.y + vel2.z*bondDir.z;
-                    mixed3 vb2 = (mixed3) (bondDir.x*dotvr2, bondDir.y*dotvr2, bondDir.z*dotvr2);
-                    mixed3 vp2 = (mixed3) (vel2.x-vb2.x, vel2.y-vb2.y, vel2.z-vb2.z);
-                    mixed vbCMass = (m1*dotvr1 + m2*dotvr2)*invTotMass;
-                    dotvr1 -= vbCMass;
-                    dotvr2 -= vbCMass;
-                    if (dotvr1 != dotvr2)
-                        deltaT = deltaR/fabs(dotvr1-dotvr2);
-                    if (deltaT > dt)
-                        deltaT = dt;
-                    mixed vBond = hardWallScale/sqrt(m1);
-                    dotvr1 = -dotvr1*vBond*m2*invTotMass/fabs(dotvr1);
-                    dotvr2 = -dotvr2*vBond*m1*invTotMass/fabs(dotvr2);
-                    mixed dr1 = -deltaR*m2*invTotMass + deltaT*dotvr1;
-                    mixed dr2 = deltaR*m1*invTotMass + deltaT*dotvr2;
-                    dotvr1 += vbCMass;
-                    dotvr2 += vbCMass;
-                    pos1.x += bondDir.x*dr1;
-                    pos1.y += bondDir.y*dr1;
-                    pos1.z += bondDir.z*dr1;
-                    pos2.x += bondDir.x*dr2;
-                    pos2.y += bondDir.y*dr2;
-                    pos2.z += bondDir.z*dr2;
-                    velm[atom.x] = (mixed4) (vp1.x + bondDir.x*dotvr1, vp1.y + bondDir.y*dotvr1, vp1.z + bondDir.z*dotvr1, velm[atom.x].w);
-                    velm[atom.y] = (mixed4) (vp2.x + bondDir.x*dotvr2, vp2.y + bondDir.y*dotvr2, vp2.z + bondDir.z*dotvr2, velm[atom.y].w);
-#ifdef USE_MIXED_PRECISION
-                    posq[atom.x] = (real4) ((real) pos1.x, (real) pos1.y, (real) pos1.z, (real) pos1.w);
-                    posq[atom.y] = (real4) ((real) pos2.x, (real) pos2.y, (real) pos2.z, (real) pos2.w);
-                    posqCorrection[atom.x] = (real4) (pos1.x-(real) pos1.x, pos1.y-(real) pos1.y, pos1.z-(real) pos1.z, 0);
-                    posqCorrection[atom.y] = (real4) (pos2.x-(real) pos2.x, pos2.y-(real) pos2.y, pos2.z-(real) pos2.z, 0);
-#else
-                    posq[atom.x] = pos1;
-                    posq[atom.y] = pos2;
-#endif
-                }
-            }
-            index += get_global_size(0);
-        }
-    }
-}
-