Merge changes from main branch

openmmapi/include/openmm/internal/PeriodicTorsionForceImpl.h

@@ -53,7 +53,7 @@ public:
     const PeriodicTorsionForce& getOwner() const {
         return owner;
     }
-    void updateContextState(ContextImpl& context) {
+    void updateContextState(ContextImpl& context, bool& forcesInvalid) {
         // This force field doesn't update the state directly.
     }
     double calcForcesAndEnergy(ContextImpl& context, bool includeForces, bool includeEnergy, int groups);

openmmapi/include/openmm/internal/RBTorsionForceImpl.h

@@ -53,7 +53,7 @@ public:
     const RBTorsionForce& getOwner() const {
         return owner;
     }
-    void updateContextState(ContextImpl& context) {
+    void updateContextState(ContextImpl& context, bool& forcesInvalid) {
         // This force field doesn't update the state directly.
     }
     double calcForcesAndEnergy(ContextImpl& context, bool includeForces, bool includeEnergy, int groups);

openmmapi/src/AndersenThermostatImpl.cpp

@@ -47,7 +47,7 @@ void AndersenThermostatImpl::initialize(ContextImpl& context) {
     kernel.getAs<ApplyAndersenThermostatKernel>().initialize(context.getSystem(), owner);
 }
 
-void AndersenThermostatImpl::updateContextState(ContextImpl& context) {
+void AndersenThermostatImpl::updateContextState(ContextImpl& context, bool& forcesInvalid) {
     kernel.getAs<ApplyAndersenThermostatKernel>().execute(context);
 }
 

openmmapi/src/CMMotionRemoverImpl.cpp

@@ -48,7 +48,7 @@ void CMMotionRemoverImpl::initialize(ContextImpl& context) {
     kernel.getAs<RemoveCMMotionKernel>().initialize(system, owner);
 }
 
-void CMMotionRemoverImpl::updateContextState(ContextImpl& context) {
+void CMMotionRemoverImpl::updateContextState(ContextImpl& context, bool& forcesInvalid) {
     kernel.getAs<RemoveCMMotionKernel>().execute(context);
 }
 

openmmapi/src/Context.cpp

@@ -40,16 +40,25 @@
 using namespace OpenMM;
 using namespace std;
 
+Context::Context(const System& system, Integrator& integrator, ContextImpl& linked) : properties(linked.getOwner().properties) {
+    // This is used by ContextImpl::createLinkedContext().
+    impl = new ContextImpl(*this, system, integrator, &linked.getPlatform(), properties, &linked);
+    impl->initialize();
+}
+
 Context::Context(const System& system, Integrator& integrator) : properties(map<string, string>()) {
     impl = new ContextImpl(*this, system, integrator, 0, properties);
+    impl->initialize();
 }
 
 Context::Context(const System& system, Integrator& integrator, Platform& platform) : properties(map<string, string>()) {
     impl = new ContextImpl(*this, system, integrator, &platform, properties);
+    impl->initialize();
 }
 
 Context::Context(const System& system, Integrator& integrator, Platform& platform, const map<string, string>& properties) : properties(properties) {
     impl = new ContextImpl(*this, system, integrator, &platform, properties);
+    impl->initialize();
 }
 
 Context::~Context() {
@@ -240,6 +249,7 @@ void Context::reinitialize() {
     integrator.cleanup();
     delete impl;
     impl = new ContextImpl(*this, system, integrator, &platform, properties);
+    impl->initialize();
 }
 
 void Context::createCheckpoint(ostream& stream) {

openmmapi/src/ContextImpl.cpp

@@ -53,7 +53,7 @@ using namespace std;
 const static char CHECKPOINT_MAGIC_BYTES[] = "OpenMM Binary Checkpoint\n";
 
 
-ContextImpl::ContextImpl(Context& owner, const System& system, Integrator& integrator, Platform* platform, const map<string, string>& properties) :
+ContextImpl::ContextImpl(Context& owner, const System& system, Integrator& integrator, Platform* platform, const map<string, string>& properties, ContextImpl* originalContext) :
         owner(owner), system(system), integrator(integrator), hasInitializedForces(false), hasSetPositions(false), integratorIsDeleted(false),
         lastForceGroups(-1), platform(platform), platformData(NULL) {
     int numParticles = system.getNumParticles();
@@ -119,8 +119,6 @@ ContextImpl::ContextImpl(Context& owner, const System& system, Integrator& integ
     kernelNames.push_back(VirtualSitesKernel::Name());
     for (int i = 0; i < system.getNumForces(); ++i) {
         forceImpls.push_back(system.getForce(i).createImpl());
-        map<string, double> forceParameters = forceImpls[forceImpls.size()-1]->getDefaultParameters();
-        parameters.insert(forceParameters.begin(), forceParameters.end());
         vector<string> forceKernels = forceImpls[forceImpls.size()-1]->getKernelNames();
         kernelNames.insert(kernelNames.begin(), forceKernels.begin(), forceKernels.end());
     }
@@ -154,7 +152,10 @@ ContextImpl::ContextImpl(Context& owner, const System& system, Integrator& integ
     for (int i = candidatePlatforms.size()-1; i >= 0; i--) {
         try {
             this->platform = platform = candidatePlatforms[i].second;
+            if (originalContext == NULL)
                 platform->contextCreated(*this, validatedProperties);
+            else
+                platform->linkedContextCreated(*this, *originalContext);
             break;
         }
         catch (...) {
@@ -163,7 +164,9 @@ ContextImpl::ContextImpl(Context& owner, const System& system, Integrator& integ
             throw;
         }
     }
+}
 
+void ContextImpl::initialize() {
     // Create and initialize kernels and other objects.
     
     initializeForcesKernel = platform->createKernel(CalcForcesAndEnergyKernel::Name(), *this);
@@ -177,10 +180,13 @@ ContextImpl::ContextImpl(Context& owner, const System& system, Integrator& integ
     Vec3 periodicBoxVectors[3];
     system.getDefaultPeriodicBoxVectors(periodicBoxVectors[0], periodicBoxVectors[1], periodicBoxVectors[2]);
     updateStateDataKernel.getAs<UpdateStateDataKernel>().setPeriodicBoxVectors(*this, periodicBoxVectors[0], periodicBoxVectors[1], periodicBoxVectors[2]);
-    for (size_t i = 0; i < forceImpls.size(); ++i)
+    for (size_t i = 0; i < forceImpls.size(); ++i) {
         forceImpls[i]->initialize(*this);
+        map<string, double> forceParameters = forceImpls[i]->getDefaultParameters();
+        parameters.insert(forceParameters.begin(), forceParameters.end());
+    }
     integrator.initialize(*this);
-    updateStateDataKernel.getAs<UpdateStateDataKernel>().setVelocities(*this, vector<Vec3>(numParticles));
+    updateStateDataKernel.getAs<UpdateStateDataKernel>().setVelocities(*this, vector<Vec3>(system.getNumParticles()));
 }
 
 ContextImpl::~ContextImpl() {
@@ -301,7 +307,7 @@ double ContextImpl::calcForcesAndEnergy(bool includeForces, bool includeEnergy,
     }
 }
 
-int ContextImpl::getLastForceGroups() const {
+int& ContextImpl::getLastForceGroups() {
     return lastForceGroups;
 }
 
@@ -309,9 +315,11 @@ double ContextImpl::calcKineticEnergy() {
     return integrator.computeKineticEnergy();
 }
 
-void ContextImpl::updateContextState() {
+bool ContextImpl::updateContextState() {
+    bool forcesInvalid = false;
     for (auto force : forceImpls)
-        force->updateContextState(*this);
+        force->updateContextState(*this, forcesInvalid);
+    return forcesInvalid;
 }
 
 const vector<ForceImpl*>& ContextImpl::getForceImpls() const {
@@ -478,3 +486,7 @@ void ContextImpl::loadCheckpoint(istream& stream) {
 void ContextImpl::systemChanged() {
     integrator.stateChanged(State::Energy);
 }
+
+Context* ContextImpl::createLinkedContext(const System& system, Integrator& integrator) {
+    return new Context(system, integrator, *this);
+}

openmmapi/src/CustomCVForce.cpp

+/* -------------------------------------------------------------------------- *
+ *                                   OpenMM                                   *
+ * -------------------------------------------------------------------------- *
+ * This is part of the OpenMM molecular simulation toolkit originating from   *
+ * Simbios, the NIH National Center for Physics-Based Simulation of           *
+ * Biological Structures at Stanford, funded under the NIH Roadmap for        *
+ * Medical Research, grant U54 GM072970. See https://simtk.org.               *
+ *                                                                            *
+ * Portions copyright (c) 2008-2017 Stanford University and the Authors.      *
+ * Authors: Peter Eastman                                                     *
+ * Contributors:                                                              *
+ *                                                                            *
+ * Permission is hereby granted, free of charge, to any person obtaining a    *
+ * copy of this software and associated documentation files (the "Software"), *
+ * to deal in the Software without restriction, including without limitation  *
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,   *
+ * and/or sell copies of the Software, and to permit persons to whom the      *
+ * Software is furnished to do so, subject to the following conditions:       *
+ *                                                                            *
+ * The above copyright notice and this permission notice shall be included in *
+ * all copies or substantial portions of the Software.                        *
+ *                                                                            *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR *
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,   *
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL    *
+ * THE AUTHORS, CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,    *
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR      *
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE  *
+ * USE OR OTHER DEALINGS IN THE SOFTWARE.                                     *
+ * -------------------------------------------------------------------------- */
+
+#include "openmm/OpenMMException.h"
+#include "openmm/CustomCVForce.h"
+#include "openmm/internal/AssertionUtilities.h"
+#include "openmm/internal/CustomCVForceImpl.h"
+#include <cmath>
+#include <map>
+#include <set>
+#include <utility>
+
+using namespace OpenMM;
+using namespace std;
+
+CustomCVForce::CustomCVForce(const string& energy) : energyExpression(energy) {
+}
+
+CustomCVForce::~CustomCVForce() {
+    for (auto variable : variables)
+        delete variable.variable;
+    for (auto function : functions)
+        delete function.function;
+}
+
+const string& CustomCVForce::getEnergyFunction() const {
+    return energyExpression;
+}
+
+void CustomCVForce::setEnergyFunction(const std::string& energy) {
+    energyExpression = energy;
+}
+
+int CustomCVForce::addCollectiveVariable(const std::string& name, Force* variable) {
+    if (variables.size() >= 32)
+        throw OpenMMException("CustomCVForce cannot have more than 32 collective variables");
+    variables.push_back(VariableInfo(name, variable));
+    return variables.size()-1;
+}
+
+const string& CustomCVForce::getCollectiveVariableName(int index) const {
+    ASSERT_VALID_INDEX(index, variables);
+    return variables[index].name;
+}
+
+Force& CustomCVForce::getCollectiveVariable(int index) {
+    ASSERT_VALID_INDEX(index, variables);
+    return *variables[index].variable;
+}
+
+const Force& CustomCVForce::getCollectiveVariable(int index) const {
+    ASSERT_VALID_INDEX(index, variables);
+    return *variables[index].variable;
+}
+
+int CustomCVForce::addGlobalParameter(const string& name, double defaultValue) {
+    globalParameters.push_back(GlobalParameterInfo(name, defaultValue));
+    return globalParameters.size()-1;
+}
+
+const string& CustomCVForce::getGlobalParameterName(int index) const {
+    ASSERT_VALID_INDEX(index, globalParameters);
+    return globalParameters[index].name;
+}
+
+void CustomCVForce::setGlobalParameterName(int index, const string& name) {
+    ASSERT_VALID_INDEX(index, globalParameters);
+    globalParameters[index].name = name;
+}
+
+double CustomCVForce::getGlobalParameterDefaultValue(int index) const {
+    ASSERT_VALID_INDEX(index, globalParameters);
+    return globalParameters[index].defaultValue;
+}
+
+void CustomCVForce::setGlobalParameterDefaultValue(int index, double defaultValue) {
+    ASSERT_VALID_INDEX(index, globalParameters);
+    globalParameters[index].defaultValue = defaultValue;
+}
+
+void CustomCVForce::addEnergyParameterDerivative(const string& name) {
+    for (int i = 0; i < globalParameters.size(); i++)
+        if (name == globalParameters[i].name) {
+            energyParameterDerivatives.push_back(i);
+            return;
+        }
+    throw OpenMMException(string("addEnergyParameterDerivative: Unknown global parameter '"+name+"'"));
+}
+
+const string& CustomCVForce::getEnergyParameterDerivativeName(int index) const {
+    ASSERT_VALID_INDEX(index, energyParameterDerivatives);
+    return globalParameters[energyParameterDerivatives[index]].name;
+}
+
+int CustomCVForce::addTabulatedFunction(const std::string& name, TabulatedFunction* function) {
+    functions.push_back(FunctionInfo(name, function));
+    return functions.size()-1;
+}
+
+const TabulatedFunction& CustomCVForce::getTabulatedFunction(int index) const {
+    ASSERT_VALID_INDEX(index, functions);
+    return *functions[index].function;
+}
+
+TabulatedFunction& CustomCVForce::getTabulatedFunction(int index) {
+    ASSERT_VALID_INDEX(index, functions);
+    return *functions[index].function;
+}
+
+const string& CustomCVForce::getTabulatedFunctionName(int index) const {
+    ASSERT_VALID_INDEX(index, functions);
+    return functions[index].name;
+}
+
+void CustomCVForce::getCollectiveVariableValues(Context& context, vector<double>& values) {
+    dynamic_cast<CustomCVForceImpl&>(getImplInContext(context)).getCollectiveVariableValues(getContextImpl(context), values);
+}
+
+ForceImpl* CustomCVForce::createImpl() const {
+    return new CustomCVForceImpl(*this);
+}
+
+Context& CustomCVForce::getInnerContext(Context& context) {
+    return dynamic_cast<CustomCVForceImpl&>(getImplInContext(context)).getInnerContext();
+}
+
+bool CustomCVForce::usesPeriodicBoundaryConditions() const {
+    for (auto& variable : variables)
+        if (variable.variable->usesPeriodicBoundaryConditions())
+            return true;
+    return false;
+}

openmmapi/src/CustomCVForceImpl.cpp

+/* -------------------------------------------------------------------------- *
+ *                                   OpenMM                                   *
+ * -------------------------------------------------------------------------- *
+ * This is part of the OpenMM molecular simulation toolkit originating from   *
+ * Simbios, the NIH National Center for Physics-Based Simulation of           *
+ * Biological Structures at Stanford, funded under the NIH Roadmap for        *
+ * Medical Research, grant U54 GM072970. See https://simtk.org.               *
+ *                                                                            *
+ * Portions copyright (c) 2008-2017 Stanford University and the Authors.      *
+ * Authors: Peter Eastman                                                     *
+ * Contributors:                                                              *
+ *                                                                            *
+ * Permission is hereby granted, free of charge, to any person obtaining a    *
+ * copy of this software and associated documentation files (the "Software"), *
+ * to deal in the Software without restriction, including without limitation  *
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,   *
+ * and/or sell copies of the Software, and to permit persons to whom the      *
+ * Software is furnished to do so, subject to the following conditions:       *
+ *                                                                            *
+ * The above copyright notice and this permission notice shall be included in *
+ * all copies or substantial portions of the Software.                        *
+ *                                                                            *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR *
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,   *
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL    *
+ * THE AUTHORS, CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,    *
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR      *
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE  *
+ * USE OR OTHER DEALINGS IN THE SOFTWARE.                                     *
+ * -------------------------------------------------------------------------- */
+
+#include "openmm/NonbondedForce.h"
+#include "openmm/OpenMMException.h"
+#include "openmm/internal/ContextImpl.h"
+#include "openmm/internal/CustomCVForceImpl.h"
+#include "openmm/kernels.h"
+#include "openmm/serialization/XmlSerializer.h"
+#include <map>
+
+using namespace OpenMM;
+using namespace std;
+
+CustomCVForceImpl::CustomCVForceImpl(const CustomCVForce& owner) : owner(owner), innerIntegrator(1.0),
+        innerContext(NULL) {
+}
+
+CustomCVForceImpl::~CustomCVForceImpl() {
+    if (innerContext != NULL)
+        delete innerContext;
+}
+
+void CustomCVForceImpl::initialize(ContextImpl& context) {
+    // Construct the inner system used to evaluate collective variables.
+    
+    const System& system = context.getSystem();
+    Vec3 a, b, c;
+    system.getDefaultPeriodicBoxVectors(a, b, c);
+    innerSystem.setDefaultPeriodicBoxVectors(a, b, c);
+    for (int i = 0; i < system.getNumParticles(); i++)
+        innerSystem.addParticle(system.getParticleMass(i));
+    for (int i = 0; i < owner.getNumCollectiveVariables(); i++) {
+        Force* variable = XmlSerializer::clone<Force>(owner.getCollectiveVariable(i));
+        variable->setForceGroup(i);
+        NonbondedForce* nonbonded = dynamic_cast<NonbondedForce*>(variable);
+        if (nonbonded != NULL)
+            nonbonded->setReciprocalSpaceForceGroup(-1);
+        innerSystem.addForce(variable);
+    }
+    
+    // Create the inner context.
+    
+    innerContext = context.createLinkedContext(innerSystem, innerIntegrator);
+    vector<Vec3> positions(system.getNumParticles(), Vec3());
+    innerContext->setPositions(positions);
+    
+    // Create the kernel.
+    
+    kernel = context.getPlatform().createKernel(CalcCustomCVForceKernel::Name(), context);
+    kernel.getAs<CalcCustomCVForceKernel>().initialize(context.getSystem(), owner, getContextImpl(*innerContext));
+}
+
+double CustomCVForceImpl::calcForcesAndEnergy(ContextImpl& context, bool includeForces, bool includeEnergy, int groups) {
+    if ((groups&(1<<owner.getForceGroup())) != 0)
+        return kernel.getAs<CalcCustomCVForceKernel>().execute(context, getContextImpl(*innerContext), includeForces, includeEnergy);
+    return 0.0;
+}
+
+vector<string> CustomCVForceImpl::getKernelNames() {
+    vector<string> names;
+    names.push_back(CalcCustomCVForceKernel::Name());
+    return names;
+}
+
+map<string, double> CustomCVForceImpl::getDefaultParameters() {
+    map<string, double> parameters;
+    parameters.insert(innerContext->getParameters().begin(), innerContext->getParameters().end());
+    for (int i = 0; i < owner.getNumGlobalParameters(); i++)
+        parameters[owner.getGlobalParameterName(i)] = owner.getGlobalParameterDefaultValue(i);
+    return parameters;
+}
+
+void CustomCVForceImpl::getCollectiveVariableValues(ContextImpl& context, vector<double>& values) {
+    kernel.getAs<CalcCustomCVForceKernel>().copyState(context, getContextImpl(*innerContext));
+    values.clear();
+    for (int i = 0; i < innerSystem.getNumForces(); i++) {
+        double value = innerContext->getState(State::Energy, false, 1<<i).getPotentialEnergy();
+        values.push_back(value);
+    }
+}
+
+Context& CustomCVForceImpl::getInnerContext() {
+    return *innerContext;
+}

openmmapi/src/CustomIntegrator.cpp

@@ -6,7 +6,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2011-2016 Stanford University and the Authors.      *
+ * Portions copyright (c) 2011-2017 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -48,6 +48,11 @@ CustomIntegrator::CustomIntegrator(double stepSize) : globalsAreCurrent(true), f
     kineticEnergy = "m*v*v/2";
 }
 
+CustomIntegrator::~CustomIntegrator() {
+    for (auto function : functions)
+        delete function.function;
+}
+
 void CustomIntegrator::initialize(ContextImpl& contextRef) {
     if (owner != NULL && &contextRef.getOwner() != owner)
         throw OpenMMException("This Integrator is already bound to a context");
@@ -281,6 +286,26 @@ void CustomIntegrator::getComputationStep(int index, ComputationType& type, stri
     expression = computations[index].expression;
 }
 
+int CustomIntegrator::addTabulatedFunction(const std::string& name, TabulatedFunction* function) {
+    functions.push_back(FunctionInfo(name, function));
+    return functions.size()-1;
+}
+
+const TabulatedFunction& CustomIntegrator::getTabulatedFunction(int index) const {
+    ASSERT_VALID_INDEX(index, functions);
+    return *functions[index].function;
+}
+
+TabulatedFunction& CustomIntegrator::getTabulatedFunction(int index) {
+    ASSERT_VALID_INDEX(index, functions);
+    return *functions[index].function;
+}
+
+const string& CustomIntegrator::getTabulatedFunctionName(int index) const {
+    ASSERT_VALID_INDEX(index, functions);
+    return functions[index].name;
+}
+
 const string& CustomIntegrator::getKineticEnergyExpression() const {
     return kineticEnergy;
 }

openmmapi/src/CustomIntegratorUtilities.cpp

@@ -37,6 +37,7 @@
 #include <algorithm>
 #include <set>
 #include <sstream>
+#include <utility>
 
 using namespace OpenMM;
 using namespace std;
@@ -71,7 +72,7 @@ bool CustomIntegratorUtilities::usesVariable(const Lepton::ParsedExpression& exp
 
 void CustomIntegratorUtilities::analyzeComputations(const ContextImpl& context, const CustomIntegrator& integrator, vector<vector<Lepton::ParsedExpression> >& expressions,
             vector<Comparison>& comparisons, vector<int>& blockEnd, vector<bool>& invalidatesForces, vector<bool>& needsForces, vector<bool>& needsEnergy,
-            vector<bool>& computeBoth, vector<int>& forceGroup) {
+            vector<bool>& computeBoth, vector<int>& forceGroup, const map<string, Lepton::CustomFunction*>& functions) {
     int numSteps = integrator.getNumComputations();
     expressions.resize(numSteps);
     comparisons.resize(numSteps);
@@ -82,7 +83,7 @@ void CustomIntegratorUtilities::analyzeComputations(const ContextImpl& context,
     forceGroup.resize(numSteps, -2);
     vector<CustomIntegrator::ComputationType> stepType(numSteps);
     vector<string> stepVariable(numSteps);
-    map<string, Lepton::CustomFunction*> customFunctions;
+    map<string, Lepton::CustomFunction*> customFunctions = functions;
     DerivFunction derivFunction;
     customFunctions["deriv"] = &derivFunction;
 
@@ -111,7 +112,8 @@ void CustomIntegratorUtilities::analyzeComputations(const ContextImpl& context,
         for (auto& param : force->getDefaultParameters())
             affectsForce.insert(param.first);
     for (int i = 0; i < numSteps; i++)
-        invalidatesForces[i] = (stepType[i] == CustomIntegrator::ConstrainPositions || affectsForce.find(stepVariable[i]) != affectsForce.end());
+        invalidatesForces[i] = (stepType[i] == CustomIntegrator::ConstrainPositions || stepType[i] == CustomIntegrator::UpdateContextState ||
+                affectsForce.find(stepVariable[i]) != affectsForce.end());
 
     // Make a list of which steps require valid forces or energy to be known.
 
@@ -249,26 +251,23 @@ void CustomIntegratorUtilities::enumeratePaths(int firstStep, vector<int> steps,
 
 void CustomIntegratorUtilities::analyzeForceComputationsForPath(vector<int>& steps, const vector<bool>& needsForces, const vector<bool>& needsEnergy,
             const vector<bool>& invalidatesForces, const vector<int>& forceGroup, vector<bool>& computeBoth) {
-    vector<int> candidatePoints;
-    int currentGroup = -1;
+    vector<pair<int, int> > candidatePoints;
     for (int step : steps) {
-        if (invalidatesForces[step] || ((needsForces[step] || needsEnergy[step]) && forceGroup[step] != currentGroup)) {
-            // Forces and energies are invalidated at this step, or it changes to a different force group,
-            // so anything from this point on won't affect what we do at earlier steps.
+        if (invalidatesForces[step]) {
+            // Forces and energies are invalidated at this step, so anything from this point on won't affect what we do at earlier steps.
 
             candidatePoints.clear();
         }
         if (needsForces[step] || needsEnergy[step]) {
             // See if this step affects what we do at earlier points.
 
-            for (int candidate : candidatePoints)
-                if ((needsForces[candidate] && needsEnergy[step]) || (needsEnergy[candidate] && needsForces[step]))
-                    computeBoth[candidate] = true;
+            for (auto candidate : candidatePoints)
+                if (candidate.second == forceGroup[step] && ((needsForces[candidate.first] && needsEnergy[step]) || (needsEnergy[candidate.first] && needsForces[step])))
+                    computeBoth[candidate.first] = true;
 
             // Add this to the list of candidates that might be affected by later steps.
 
-            candidatePoints.push_back(step);
-            currentGroup = forceGroup[step];
+            candidatePoints.push_back(make_pair(step, forceGroup[step]));
         }
     }
 }

openmmapi/src/CustomNonbondedForceImpl.cpp

@@ -170,14 +170,17 @@ void CustomNonbondedForceImpl::calcLongRangeCorrection(const CustomNonbondedForc
     vector<vector<double> > classes;
     map<vector<double>, int> classIndex;
     vector<int> atomClass(numParticles);
-    for (int i = 0; i < numParticles; i++) {
     vector<double> parameters;
+    for (int i = 0; i < numParticles; i++) {
         force.getParticleParameters(i, parameters);
-        if (classIndex.find(parameters) == classIndex.end()) {
+        map<vector<double>, int>::iterator entry = classIndex.find(parameters);
+        if (entry == classIndex.end()) {
             classIndex[parameters] = classes.size();
+            atomClass[i] = classes.size();
             classes.push_back(parameters);
         }
-        atomClass[i] = classIndex[parameters];
+        else
+            atomClass[i] = entry->second;
     }
     int numClasses = classes.size();
     
@@ -228,10 +231,18 @@ void CustomNonbondedForceImpl::calcLongRangeCorrection(const CustomNonbondedForc
     double nPart = (double) numParticles;
     double numInteractions = (nPart*(nPart+1))/2;
     Lepton::CompiledExpression expression = Lepton::Parser::parse(force.getEnergyFunction(), functions).createCompiledExpression();
+    vector<string> paramNames;
+    for (int i = 0; i < force.getNumPerParticleParameters(); i++) {
+        stringstream name1, name2;
+        name1 << force.getPerParticleParameterName(i) << 1;
+        name2 << force.getPerParticleParameterName(i) << 2;
+        paramNames.push_back(name1.str());
+        paramNames.push_back(name2.str());
+    }
     double sum = 0;
     for (int i = 0; i < numClasses; i++)
         for (int j = i; j < numClasses; j++)
-            sum += interactionCount[make_pair(i, j)]*integrateInteraction(expression, classes[i], classes[j], force, context);
+            sum += interactionCount[make_pair(i, j)]*integrateInteraction(expression, classes[i], classes[j], force, context, paramNames);
     sum /= numInteractions;
     coefficient = 2*M_PI*nPart*nPart*sum;
     
@@ -244,23 +255,20 @@ void CustomNonbondedForceImpl::calcLongRangeCorrection(const CustomNonbondedForc
         sum = 0;
         for (int i = 0; i < numClasses; i++)
             for (int j = i; j < numClasses; j++)
-                sum += interactionCount[make_pair(i, j)]*integrateInteraction(expression, classes[i], classes[j], force, context);
+                sum += interactionCount[make_pair(i, j)]*integrateInteraction(expression, classes[i], classes[j], force, context, paramNames);
         sum /= numInteractions;
         derivatives[k] = 2*M_PI*nPart*nPart*sum;
     }
 }
 
 double CustomNonbondedForceImpl::integrateInteraction(Lepton::CompiledExpression& expression, const vector<double>& params1, const vector<double>& params2,
-        const CustomNonbondedForce& force, const Context& context) {
+        const CustomNonbondedForce& force, const Context& context, const vector<string>& paramNames) {
     const set<string>& variables = expression.getVariables();
     for (int i = 0; i < force.getNumPerParticleParameters(); i++) {
-        stringstream name1, name2;
-        name1 << force.getPerParticleParameterName(i) << 1;
-        name2 << force.getPerParticleParameterName(i) << 2;
-        if (variables.find(name1.str()) != variables.end())
-            expression.getVariableReference(name1.str()) = params1[i];
-        if (variables.find(name2.str()) != variables.end())
-            expression.getVariableReference(name2.str()) = params2[i];
+        if (variables.find(paramNames[2*i]) != variables.end())
+            expression.getVariableReference(paramNames[2*i]) = params1[i];
+        if (variables.find(paramNames[2*i+1]) != variables.end())
+            expression.getVariableReference(paramNames[2*i+1]) = params2[i];
     }
     for (int i = 0; i < force.getNumGlobalParameters(); i++) {
         const string& name = force.getGlobalParameterName(i);

openmmapi/src/ForceImpl.cpp

+/* -------------------------------------------------------------------------- *
+ *                                   OpenMM                                   *
+ * -------------------------------------------------------------------------- *
+ * This is part of the OpenMM molecular simulation toolkit originating from   *
+ * Simbios, the NIH National Center for Physics-Based Simulation of           *
+ * Biological Structures at Stanford, funded under the NIH Roadmap for        *
+ * Medical Research, grant U54 GM072970. See https://simtk.org.               *
+ *                                                                            *
+ * Portions copyright (c) 2017 Stanford University and the Authors.           *
+ * Authors: Peter Eastman                                                     *
+ * Contributors:                                                              *
+ *                                                                            *
+ * Permission is hereby granted, free of charge, to any person obtaining a    *
+ * copy of this software and associated documentation files (the "Software"), *
+ * to deal in the Software without restriction, including without limitation  *
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,   *
+ * and/or sell copies of the Software, and to permit persons to whom the      *
+ * Software is furnished to do so, subject to the following conditions:       *
+ *                                                                            *
+ * The above copyright notice and this permission notice shall be included in *
+ * all copies or substantial portions of the Software.                        *
+ *                                                                            *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR *
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,   *
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL    *
+ * THE AUTHORS, CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,    *
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR      *
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE  *
+ * USE OR OTHER DEALINGS IN THE SOFTWARE.                                     *
+ * -------------------------------------------------------------------------- */
+
+#include "openmm/internal/ForceImpl.h"
+
+using namespace OpenMM;
+using namespace std;
+
+void ForceImpl::updateContextState(ContextImpl& context, bool& forcesInvalid) {
+    // Usually subclasses will override this.  If they don't, call the old
+    // (single argument) version instead, and just assume they invalidate forces.
+
+    updateContextState(context);
+    forcesInvalid = true;
+}
+
+void ForceImpl::updateContextState(ContextImpl& context) {
+}

openmmapi/src/MonteCarloBarostatImpl.cpp

@@ -6,7 +6,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2010-2016 Stanford University and the Authors.      *
+ * Portions copyright (c) 2010-2017 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -68,7 +68,7 @@ void MonteCarloBarostatImpl::initialize(ContextImpl& context) {
     init_gen_rand(randSeed, random);
 }
 
-void MonteCarloBarostatImpl::updateContextState(ContextImpl& context) {
+void MonteCarloBarostatImpl::updateContextState(ContextImpl& context, bool& forcesInvalid) {
     if (++step < owner.getFrequency() || owner.getFrequency() == 0)
         return;
     step = 0;
@@ -101,8 +101,10 @@ void MonteCarloBarostatImpl::updateContextState(ContextImpl& context) {
         context.getOwner().setPeriodicBoxVectors(box[0], box[1], box[2]);
         volume = newVolume;
     }
-    else
+    else {
         numAccepted++;
+        forcesInvalid = true;
+    }
     numAttempted++;
     if (numAttempted >= 10) {
         if (numAccepted < 0.25*numAttempted) {

openmmapi/src/SplineFitter.cpp

@@ -568,7 +568,7 @@ void SplineFitter::create3DNaturalSpline(const vector<double>& x, const vector<d
                 int nextk = k+1;
                 double deltax = x[nexti]-x[i];
                 double deltay = y[nextj]-y[j];
-                double deltaz = z[nextj]-z[j];
+                double deltaz = z[nextk]-z[k];
                 double e[] = {values[i+j*xsize+k*xysize], values[nexti+j*xsize+k*xysize], values[i+nextj*xsize+k*xysize], values[nexti+nextj*xsize+k*xysize], values[i+j*xsize+nextk*xysize], values[nexti+j*xsize+nextk*xysize], values[i+nextj*xsize+nextk*xysize], values[nexti+nextj*xsize+nextk*xysize]};
                 double e1[] = {d1[i+j*xsize+k*xysize], d1[nexti+j*xsize+k*xysize], d1[i+nextj*xsize+k*xysize], d1[nexti+nextj*xsize+k*xysize], d1[i+j*xsize+nextk*xysize], d1[nexti+j*xsize+nextk*xysize], d1[i+nextj*xsize+nextk*xysize], d1[nexti+nextj*xsize+nextk*xysize]};
                 double e2[] = {d2[i+j*xsize+k*xysize], d2[nexti+j*xsize+k*xysize], d2[i+nextj*xsize+k*xysize], d2[nexti+nextj*xsize+k*xysize], d2[i+j*xsize+nextk*xysize], d2[nexti+j*xsize+nextk*xysize], d2[i+nextj*xsize+nextk*xysize], d2[nexti+nextj*xsize+nextk*xysize]};

openmmapi/src/VirtualSite.cpp

@@ -6,7 +6,7 @@
  * Biological Structures at Stanford, funded under the NIH Roadmap for        *
  * Medical Research, grant U54 GM072970. See https://simtk.org.               *
  *                                                                            *
- * Portions copyright (c) 2012-2014 Stanford University and the Authors.      *
+ * Portions copyright (c) 2012-2017 Stanford University and the Authors.      *
  * Authors: Peter Eastman                                                     *
  * Contributors:                                                              *
  *                                                                            *
@@ -105,8 +105,30 @@ double OutOfPlaneSite::getWeightCross() const {
     return weightCross;
 }
 
-LocalCoordinatesSite::LocalCoordinatesSite(int particle1, int particle2, int particle3, const Vec3& originWeights, const Vec3& xWeights, const Vec3& yWeights, const Vec3& localPosition) :
+LocalCoordinatesSite::LocalCoordinatesSite(const vector<int>& particles, const vector<double>& originWeights, const vector<double>& xWeights, const vector<double>& yWeights, const Vec3& localPosition) :
         originWeights(originWeights), xWeights(xWeights), yWeights(yWeights), localPosition(localPosition) {
+    int numParticles = particles.size();
+    if (numParticles < 2)
+        throw OpenMMException("LocalCoordinatesSite: Must depend on at least two other particles");
+    if (originWeights.size() != numParticles || xWeights.size() != numParticles || yWeights.size() != numParticles)
+        throw OpenMMException("LocalCoordinatesSite: Number of weights does not match number of particles");
+    double originSum = 0, xSum = 0, ySum = 0;
+    for (int i = 0; i < numParticles; i++) {
+        originSum += originWeights[i];
+        xSum += xWeights[i];
+        ySum += yWeights[i];
+    }
+    if (fabs(originSum-1.0) > 1e-6)
+        throw OpenMMException("LocalCoordinatesSite: Weights for computing origin must add to 1");
+    if (fabs(xSum) > 1e-6)
+        throw OpenMMException("LocalCoordinatesSite: Weights for computing x axis must add to 0");
+    if (fabs(ySum) > 1e-6)
+        throw OpenMMException("LocalCoordinatesSite: Weights for computing y axis must add to 0");
+    setParticles(particles);
+}
+
+LocalCoordinatesSite::LocalCoordinatesSite(int particle1, int particle2, int particle3, const Vec3& originWeights, const Vec3& xWeights, const Vec3& yWeights, const Vec3& localPosition) :
+        localPosition(localPosition) {
     if (fabs(originWeights[0]+originWeights[1]+originWeights[2]-1.0) > 1e-6)
         throw OpenMMException("LocalCoordinatesSite: Weights for computing origin must add to 1");
     if (fabs(xWeights[0]+xWeights[1]+xWeights[2]) > 1e-6)
@@ -118,18 +140,45 @@ LocalCoordinatesSite::LocalCoordinatesSite(int particle1, int particle2, int par
     particles[1] = particle2;
     particles[2] = particle3;
     setParticles(particles);
+    this->originWeights.push_back(originWeights[0]);
+    this->originWeights.push_back(originWeights[1]);
+    this->originWeights.push_back(originWeights[2]);
+    this->xWeights.push_back(xWeights[0]);
+    this->xWeights.push_back(xWeights[1]);
+    this->xWeights.push_back(xWeights[2]);
+    this->yWeights.push_back(yWeights[0]);
+    this->yWeights.push_back(yWeights[1]);
+    this->yWeights.push_back(yWeights[2]);
+}
+
+void LocalCoordinatesSite::getOriginWeights(vector<double>& weights) const {
+    weights = originWeights;
+}
+
+Vec3 LocalCoordinatesSite::getOriginWeights() const {
+    if (originWeights.size() != 3)
+        throw OpenMMException("LocalCoordinatesSite: This version of getOriginWeights() requires the site to depend on three particles");
+    return Vec3(originWeights[0], originWeights[1], originWeights[2]);
+}
+
+void LocalCoordinatesSite::getXWeights(vector<double>& weights) const {
+    weights = xWeights;
 }
 
-const Vec3& LocalCoordinatesSite::getOriginWeights() const {
-    return originWeights;
+Vec3 LocalCoordinatesSite::getXWeights() const {
+    if (xWeights.size() != 3)
+        throw OpenMMException("LocalCoordinatesSite: This version of getXWeights() requires the site to depend on three particles");
+    return Vec3(xWeights[0], xWeights[1], xWeights[2]);
 }
 
-const Vec3& LocalCoordinatesSite::getXWeights() const {
-    return xWeights;
+void LocalCoordinatesSite::getYWeights(vector<double>& weights) const {
+    weights = yWeights;
 }
 
-const Vec3& LocalCoordinatesSite::getYWeights() const {
-    return yWeights;
+Vec3 LocalCoordinatesSite::getYWeights() const {
+    if (yWeights.size() != 3)
+        throw OpenMMException("LocalCoordinatesSite: This version of getYWeights() requires the site to depend on three particles");
+    return Vec3(yWeights[0], yWeights[1], yWeights[2]);
 }
 
 const Vec3& LocalCoordinatesSite::getLocalPosition() const {

platforms/cpu/include/CpuKernels.h

@@ -373,7 +373,7 @@ private:
 class CpuCalcCustomGBForceKernel : public CalcCustomGBForceKernel {
 public:
     CpuCalcCustomGBForceKernel(std::string name, const Platform& platform, CpuPlatform::PlatformData& data) :
-            CalcCustomGBForceKernel(name, platform), data(data) {
+            CalcCustomGBForceKernel(name, platform), data(data), ixn(NULL), neighborList(NULL) {
     }
     ~CpuCalcCustomGBForceKernel();
     /**
@@ -406,6 +406,7 @@ private:
     double **particleParamArray;
     double nonbondedCutoff;
     CpuCustomGBForce* ixn;
+    CpuNeighborList* neighborList;
     std::vector<std::set<int> > exclusions;
     std::vector<std::string> particleParameterNames, globalParameterNames, energyParamDerivNames, valueNames;
     std::vector<OpenMM::CustomGBForce::ComputationType> valueTypes;

platforms/cpu/include/CpuPlatform.h

@@ -68,6 +68,15 @@ public:
         static const std::string key = "Threads";
         return key;
     }
+    /**
+     * This is the name of the parameter for requesting that force computations be deterministic.  Setting
+     * this to "true" DOES NOT GUARANTEE that the forces will actually be fully deterministic, but it does
+     * try to reduce the variation in them at the cost of a small loss in performance.
+     */
+    static const std::string& CpuDeterministicForces() {
+        static const std::string key = "DeterministicForces";
+        return key;
+    }
     /**
      * We cannot use the standard mechanism for platform data, because that is already used by the superclass.
      * Instead, we maintain a table of ContextImpls to PlatformDatas.
@@ -80,7 +89,7 @@ private:
 
 class CpuPlatform::PlatformData {
 public:
-    PlatformData(int numParticles, int numThreads);
+    PlatformData(int numParticles, int numThreads, bool deterministicForces);
     ~PlatformData();
     void requestNeighborList(double cutoffDistance, double padding, bool useExclusions, const std::vector<std::set<int> >& exclusionList);
     AlignedArray<float> posq;
@@ -91,7 +100,7 @@ public:
     std::map<std::string, std::string> propertyValues;
     CpuNeighborList* neighborList;
     double cutoff, paddedCutoff;
-    bool anyExclusions;
+    bool anyExclusions, deterministicForces;
     std::vector<std::set<int> > exclusions;
 };
 

platforms/cpu/src/CpuKernels.cpp

@@ -642,7 +642,7 @@ double CpuCalcNonbondedForceKernel::execute(ContextImpl& context, bool includeFo
             useOptimizedPme = getPlatform().supportsKernels(kernelNames);
             if (useOptimizedPme) {
                 optimizedPme = getPlatform().createKernel(CalcPmeReciprocalForceKernel::Name(), context);
-                optimizedPme.getAs<CalcPmeReciprocalForceKernel>().initialize(gridSize[0], gridSize[1], gridSize[2], numParticles, ewaldAlpha);
+                optimizedPme.getAs<CalcPmeReciprocalForceKernel>().initialize(gridSize[0], gridSize[1], gridSize[2], numParticles, ewaldAlpha, data.deterministicForces);
             }
         }
         if (nonbondedMethod == LJPME) {
@@ -653,10 +653,10 @@ double CpuCalcNonbondedForceKernel::execute(ContextImpl& context, bool includeFo
             useOptimizedPme = getPlatform().supportsKernels(kernelNames);
             if (useOptimizedPme) {
                 optimizedPme = getPlatform().createKernel(CalcPmeReciprocalForceKernel::Name(), context);
-                optimizedPme.getAs<CalcPmeReciprocalForceKernel>().initialize(gridSize[0], gridSize[1], gridSize[2], numParticles, ewaldAlpha);
+                optimizedPme.getAs<CalcPmeReciprocalForceKernel>().initialize(gridSize[0], gridSize[1], gridSize[2], numParticles, ewaldAlpha, data.deterministicForces);
                 optimizedDispersionPme = getPlatform().createKernel(CalcDispersionPmeReciprocalForceKernel::Name(), context);
                 optimizedDispersionPme.getAs<CalcDispersionPmeReciprocalForceKernel>().initialize(dispersionGridSize[0], dispersionGridSize[1],
-                                                                                                  dispersionGridSize[2], numParticles, ewaldDispersionAlpha);
+                                                                                                  dispersionGridSize[2], numParticles, ewaldDispersionAlpha, data.deterministicForces);
             }
         }
     }
@@ -1018,6 +1018,8 @@ CpuCalcCustomGBForceKernel::~CpuCalcCustomGBForceKernel() {
     }
     if (ixn != NULL)
         delete ixn;
+    if (neighborList != NULL)
+        delete neighborList;
 }
 
 void CpuCalcCustomGBForceKernel::initialize(const System& system, const CustomGBForce& force) {
@@ -1064,7 +1066,7 @@ void CpuCalcCustomGBForceKernel::initialize(const System& system, const CustomGB
     nonbondedMethod = CalcCustomGBForceKernel::NonbondedMethod(force.getNonbondedMethod());
     nonbondedCutoff = force.getCutoffDistance();
     if (nonbondedMethod != NoCutoff)
-        data.requestNeighborList(nonbondedCutoff, 0.25*nonbondedCutoff, force.getNumExclusions() > 0, exclusions);
+        neighborList = new CpuNeighborList(4);
 
     // Create custom functions for the tabulated functions.
 
@@ -1171,7 +1173,8 @@ double CpuCalcCustomGBForceKernel::execute(ContextImpl& context, bool includeFor
         ixn->setPeriodic(extractBoxSize(context));
     if (nonbondedMethod != NoCutoff) {
         vector<set<int> > noExclusions(numParticles);
-        ixn->setUseCutoff(nonbondedCutoff, *data.neighborList);
+        neighborList->computeNeighborList(numParticles, data.posq, noExclusions, boxVectors, data.isPeriodic, nonbondedCutoff, data.threads);
+        ixn->setUseCutoff(nonbondedCutoff, *neighborList);
     }
     map<string, double> globalParameters;
     for (auto& name : globalParameterNames)

platforms/cpu/src/CpuPlatform.cpp

@@ -37,6 +37,7 @@
 #include "openmm/OpenMMException.h"
 #include "openmm/internal/hardware.h"
 #include "openmm/internal/vectorize.h"
+#include <algorithm>
 #include <sstream>
 #include <stdlib.h>
 
@@ -74,6 +75,7 @@ CpuPlatform::CpuPlatform() {
     registerKernelFactory(CalcGayBerneForceKernel::Name(), factory);
     registerKernelFactory(IntegrateLangevinStepKernel::Name(), factory);
     platformProperties.push_back(CpuThreads());
+    platformProperties.push_back(CpuDeterministicForces());
     int threads = getNumProcessors();
     char* threadsEnv = getenv("OPENMM_CPU_THREADS");
     if (threadsEnv != NULL)
@@ -81,6 +83,7 @@ CpuPlatform::CpuPlatform() {
     stringstream defaultThreads;
     defaultThreads << threads;
     setPropertyDefaultValue(CpuThreads(), defaultThreads.str());
+    setPropertyDefaultValue(CpuDeterministicForces(), "false");
 }
 
 const string& CpuPlatform::getPropertyValue(const Context& context, const string& property) const {
@@ -111,9 +114,13 @@ void CpuPlatform::contextCreated(ContextImpl& context, const map<string, string>
     ReferencePlatform::contextCreated(context, properties);
     const string& threadsPropValue = (properties.find(CpuThreads()) == properties.end() ?
             getPropertyDefaultValue(CpuThreads()) : properties.find(CpuThreads())->second);
+    string deterministicForcesValue = (properties.find(CpuDeterministicForces()) == properties.end() ?
+            getPropertyDefaultValue(CpuDeterministicForces()) : properties.find(CpuDeterministicForces())->second);
     int numThreads;
     stringstream(threadsPropValue) >> numThreads;
-    PlatformData* data = new PlatformData(context.getSystem().getNumParticles(), numThreads);
+    transform(deterministicForcesValue.begin(), deterministicForcesValue.end(), deterministicForcesValue.begin(), ::tolower);
+    bool deterministicForces = (deterministicForcesValue == "true");
+    PlatformData* data = new PlatformData(context.getSystem().getNumParticles(), numThreads, deterministicForces);
     contextData[&context] = data;
     ReferenceConstraints& constraints = *(ReferenceConstraints*) reinterpret_cast<ReferencePlatform::PlatformData*>(context.getPlatformData())->constraints;
     if (constraints.settle != NULL) {
@@ -139,8 +146,8 @@ const CpuPlatform::PlatformData& CpuPlatform::getPlatformData(const ContextImpl&
     return *contextData[&context];
 }
 
-CpuPlatform::PlatformData::PlatformData(int numParticles, int numThreads) : posq(4*numParticles), threads(numThreads),
-        neighborList(NULL), cutoff(0.0), paddedCutoff(0.0), anyExclusions(false) {
+CpuPlatform::PlatformData::PlatformData(int numParticles, int numThreads, bool deterministicForces) : posq(4*numParticles), threads(numThreads),
+        deterministicForces(deterministicForces), neighborList(NULL), cutoff(0.0), paddedCutoff(0.0), anyExclusions(false) {
     numThreads = threads.getNumThreads();
     threadForce.resize(numThreads);
     for (int i = 0; i < numThreads; i++)
@@ -149,6 +156,7 @@ CpuPlatform::PlatformData::PlatformData(int numParticles, int numThreads) : posq
     stringstream threadsProperty;
     threadsProperty << numThreads;
     propertyValues[CpuThreads()] = threadsProperty.str();
+    propertyValues[CpuDeterministicForces()] = deterministicForces ? "true" : "false";
 }
 
 CpuPlatform::PlatformData::~PlatformData() {

platforms/cuda/include/CudaContext.h

@@ -77,7 +77,8 @@ public:
     static const int ThreadBlockSize;
     static const int TileSize;
     CudaContext(const System& system, int deviceIndex, bool useBlockingSync, const std::string& precision,
-            const std::string& compiler, const std::string& tempDir, const std::string& hostCompiler, CudaPlatform::PlatformData& platformData);
+            const std::string& compiler, const std::string& tempDir, const std::string& hostCompiler, CudaPlatform::PlatformData& platformData,
+            CudaContext* originalContext);
     ~CudaContext();
     /**
      * This is called to initialize internal data structures after all Forces in the system
@@ -284,6 +285,10 @@ public:
      * Clear all buffers that have been registered with addAutoclearBuffer().
      */
     void clearAutoclearBuffers();
+    /**
+     * Sum the buffer containing energy.
+     */
+    double reduceEnergy();
     /**
      * Get the current simulation time.
      */
@@ -622,6 +627,7 @@ private:
     int numAtomBlocks;
     int numThreadBlocks;
     bool useBlockingSync, useDoublePrecision, useMixedPrecision, contextIsValid, atomsWereReordered, boxIsTriclinic, hasCompilerKernel, isNvccAvailable, forcesValid;
+    bool isLinkedContext;
     std::string compiler, tempDir, cacheDir, gpuArchitecture;
     float4 periodicBoxVecXFloat, periodicBoxVecYFloat, periodicBoxVecZFloat, periodicBoxSizeFloat, invPeriodicBoxSizeFloat;
     double4 periodicBoxVecX, periodicBoxVecY, periodicBoxVecZ, periodicBoxSize, invPeriodicBoxSize;
@@ -636,6 +642,7 @@ private:
     CUfunction clearFourBuffersKernel;
     CUfunction clearFiveBuffersKernel;
     CUfunction clearSixBuffersKernel;
+    CUfunction reduceEnergyKernel;
     CUfunction setChargesKernel;
     std::vector<CudaForceInfo*> forces;
     std::vector<Molecule> molecules;
@@ -647,6 +654,7 @@ private:
     CudaArray* velm;
     CudaArray* force;
     CudaArray* energyBuffer;
+    CudaArray* energySum;
     CudaArray* energyParamDerivBuffer;
     CudaArray* atomIndexDevice;
     CudaArray* chargeBuffer;