CUDA allows different force groups to have different cutoffs

platforms/cuda/include/CudaKernels.h

@@ -752,7 +752,7 @@ public:
      */
     void copyParametersToContext(ContextImpl& context, const GBSAOBCForce& force);
 private:
-    double prefactor, surfaceAreaFactor;
+    double prefactor, surfaceAreaFactor, cutoff;
     bool hasCreatedKernels;
     int maxTiles;
     CudaContext& cu;
@@ -802,6 +802,7 @@ public:
      */
     void copyParametersToContext(ContextImpl& context, const CustomGBForce& force);
 private:
+    double cutoff;
     bool hasInitializedKernels, needParameterGradient;
     int maxTiles, numComputedValues;
     CudaContext& cu;

platforms/cuda/include/CudaNonbondedUtilities.h

@@ -129,31 +129,17 @@ public:
         return forceThreadBlockSize;
     }
     /**
-     * Get the cutoff distance.
+     * Get the maximum cutoff distance used by any force group.
      */
-    double getCutoffDistance() {
-        return cutoff;
-    }
-    /**
-     * Get whether any interactions have been added.
-     */
-    bool getHasInteractions() {
-        return cutoff != -1.0;
-    }
-    /**
-     * Get the force group in which nonbonded interactions should be computed.
-     */
-    int getForceGroup() {
-        return nonbondedForceGroup;
-    }
+    double getMaxCutoffDistance();
     /**
      * Prepare to compute interactions.  This updates the neighbor list.
      */
-    void prepareInteractions();
+    void prepareInteractions(int forceGroups);
     /**
      * Compute the nonbonded interactions.
      */
-    void computeInteractions();
+    void computeInteractions(int forceGroups);
     /**
      * Check to see if the neighbor list arrays are large enough, and make them bigger if necessary.
      */
@@ -246,16 +232,20 @@ public:
      * @param arguments     arrays (other than per-atom parameters) that should be passed as arguments to the kernel
      * @param useExclusions specifies whether exclusions are applied to this interaction
      * @param isSymmetric   specifies whether the interaction is symmetric
+     * @param groups        the set of force groups this kernel is for
      */
-    CUfunction createInteractionKernel(const std::string& source, std::vector<ParameterInfo>& params, std::vector<ParameterInfo>& arguments, bool useExclusions, bool isSymmetric);
+    CUfunction createInteractionKernel(const std::string& source, std::vector<ParameterInfo>& params, std::vector<ParameterInfo>& arguments, bool useExclusions, bool isSymmetric, int groups);
+    /**
+     * Create the set of kernels that will be needed for a particular combination of force groups.
+     * 
+     * @param groups    the set of force groups
+     */
+    void createKernelsForGroups(int groups);
 private:
+    class KernelSet;
     class BlockSortTrait;
     CudaContext& context;
-    CUfunction forceKernel;
-    CUfunction findBlockBoundsKernel;
-    CUfunction sortBoxDataKernel;
-    CUfunction findInteractingBlocksKernel;
-    CUfunction findInteractionsWithinBlocksKernel;
+    std::map<int, KernelSet> groupKernels;
     CudaArray* exclusionTiles;
     CudaArray* exclusions;
     CudaArray* exclusionIndices;
@@ -275,11 +265,26 @@ private:
     std::vector<std::vector<int> > atomExclusions;
     std::vector<ParameterInfo> parameters;
     std::vector<ParameterInfo> arguments;
-    std::string kernelSource;
-    std::map<std::string, std::string> kernelDefines;
-    double cutoff;
+    std::map<int, double> groupCutoff;
+    std::map<int, std::string> groupKernelSource;
+    double lastCutoff;
     bool useCutoff, usePeriodic, anyExclusions, usePadding, forceRebuildNeighborList;
-    int startTileIndex, numTiles, startBlockIndex, numBlocks, maxTiles, numForceThreadBlocks, forceThreadBlockSize, nonbondedForceGroup, numAtoms;
+    int startTileIndex, numTiles, startBlockIndex, numBlocks, maxTiles, maxExclusions, numForceThreadBlocks, forceThreadBlockSize, numAtoms, groupFlags;
+};
+
+/**
+ * This class stores the kernels to execute for a set of force groups.
+ */
+
+class CudaNonbondedUtilities::KernelSet {
+public:
+    bool hasForces;
+    double cutoffDistance;
+    CUfunction forceKernel;
+    CUfunction findBlockBoundsKernel;
+    CUfunction sortBoxDataKernel;
+    CUfunction findInteractingBlocksKernel;
+    CUfunction findInteractionsWithinBlocksKernel;
 };
 
 /**

platforms/cuda/src/CudaContext.cpp

@@ -49,6 +49,7 @@
 #include <fstream>
 #include <iomanip>
 #include <iostream>
+#include <set>
 #include <sstream>
 #include <typeinfo>
 #include <cudaProfiler.h>
@@ -405,13 +406,32 @@ void CudaContext::setAsCurrent() {
 }
 
 string CudaContext::replaceStrings(const string& input, const std::map<std::string, std::string>& replacements) const {
+    static set<char> symbolChars;
+    if (symbolChars.size() == 0) {
+        symbolChars.insert('_');
+        for (char c = 'a'; c <= 'z'; c++)
+            symbolChars.insert(c);
+        for (char c = 'A'; c <= 'Z'; c++)
+            symbolChars.insert(c);
+        for (char c = '0'; c <= '9'; c++)
+            symbolChars.insert(c);
+    }
     string result = input;
     for (map<string, string>::const_iterator iter = replacements.begin(); iter != replacements.end(); iter++) {
-        int index = -1;
+        int index = 0;
+        int size = iter->first.size();
         do {
-            index = result.find(iter->first);
-            if (index != result.npos)
-                result.replace(index, iter->first.size(), iter->second);
+            index = result.find(iter->first, index);
+            if (index != result.npos) {
+                if ((index == 0 || symbolChars.find(result[index-1]) == symbolChars.end()) && (index == result.size()-size || symbolChars.find(result[index+size]) == symbolChars.end())) {
+                    // We have found a complete symbol, not part of a longer symbol.
+                    
+                    result.replace(index, size, iter->second);
+                    index += iter->second.size();
+                }
+                else
+                    index++;
+            }
         } while (index != result.npos);
     }
     return result;
@@ -1216,7 +1236,7 @@ void CudaContext::reorderAtomsImpl() {
         if (useHilbert)
             binWidth = (Real) (max(max(maxx-minx, maxy-miny), maxz-minz)/255.0);
         else
-            binWidth = (Real) (0.2*nonbonded->getCutoffDistance());
+            binWidth = (Real) (0.2*nonbonded->getMaxCutoffDistance());
         Real invBinWidth = (Real) (1.0/binWidth);
         int xbins = 1 + (int) ((maxx-minx)*invBinWidth);
         int ybins = 1 + (int) ((maxy-miny)*invBinWidth);

platforms/cuda/src/CudaKernels.cpp

@@ -98,16 +98,13 @@ void CudaCalcForcesAndEnergyKernel::beginComputation(ContextImpl& context, bool
     for (vector<CudaContext::ForcePreComputation*>::iterator iter = cu.getPreComputations().begin(); iter != cu.getPreComputations().end(); ++iter)
         (*iter)->computeForceAndEnergy(includeForces, includeEnergy, groups);
     CudaNonbondedUtilities& nb = cu.getNonbondedUtilities();
-    bool includeNonbonded = ((groups&(1<<nb.getForceGroup())) != 0);
     cu.setComputeForceCount(cu.getComputeForceCount()+1);
-    if (includeNonbonded)
-        nb.prepareInteractions();
+    nb.prepareInteractions(groups);
 }
 
 double CudaCalcForcesAndEnergyKernel::finishComputation(ContextImpl& context, bool includeForces, bool includeEnergy, int groups, bool& valid) {
     cu.getBondedUtilities().computeInteractions(groups);
-    if ((groups&(1<<cu.getNonbondedUtilities().getForceGroup())) != 0)
-        cu.getNonbondedUtilities().computeInteractions();
+    cu.getNonbondedUtilities().computeInteractions(groups);
     double sum = 0.0;
     for (vector<CudaContext::ForcePostComputation*>::iterator iter = cu.getPostComputations().begin(); iter != cu.getPostComputations().end(); ++iter)
         sum += (*iter)->computeForceAndEnergy(includeForces, includeEnergy, groups);
@@ -2570,8 +2567,9 @@ void CudaCalcGBSAOBCForceKernel::initialize(const System& system, const GBSAOBCF
     surfaceAreaFactor = -6.0*4*M_PI*force.getSurfaceAreaEnergy();
     bool useCutoff = (force.getNonbondedMethod() != GBSAOBCForce::NoCutoff);
     bool usePeriodic = (force.getNonbondedMethod() != GBSAOBCForce::NoCutoff && force.getNonbondedMethod() != GBSAOBCForce::CutoffNonPeriodic);
+    cutoff = force.getCutoffDistance();
     string source = CudaKernelSources::gbsaObc2;
-    nb.addInteraction(useCutoff, usePeriodic, false, force.getCutoffDistance(), vector<vector<int> >(), source, force.getForceGroup());
+    nb.addInteraction(useCutoff, usePeriodic, false, cutoff, vector<vector<int> >(), source, force.getForceGroup());
     nb.addParameter(CudaNonbondedUtilities::ParameterInfo("obcParams", "float", 2, sizeof(float2), params->getDevicePointer()));;
     nb.addParameter(CudaNonbondedUtilities::ParameterInfo("bornForce", "long long", 1, sizeof(long long), bornForce->getDevicePointer()));;
     cu.addForce(new CudaGBSAOBCForceInfo(force));
@@ -2591,8 +2589,8 @@ double CudaCalcGBSAOBCForceKernel::execute(ContextImpl& context, bool includeFor
             defines["USE_PERIODIC"] = "1";
         if (cu.getComputeCapability() >= 3.0 && !cu.getUseDoublePrecision())
             defines["ENABLE_SHUFFLE"] = "1";
-        defines["CUTOFF_SQUARED"] = cu.doubleToString(nb.getCutoffDistance()*nb.getCutoffDistance());
-        defines["CUTOFF"] = cu.doubleToString(nb.getCutoffDistance());
+        defines["CUTOFF_SQUARED"] = cu.doubleToString(cutoff*cutoff);
+        defines["CUTOFF"] = cu.doubleToString(cutoff);
         defines["PREFACTOR"] = cu.doubleToString(prefactor);
         defines["SURFACE_AREA_FACTOR"] = cu.doubleToString(surfaceAreaFactor);
         defines["NUM_ATOMS"] = cu.intToString(cu.getNumAtoms());
@@ -2764,6 +2762,7 @@ void CudaCalcCustomGBForceKernel::initialize(const System& system, const CustomG
     cu.setAsCurrent();
     if (cu.getPlatformData().contexts.size() > 1)
         throw OpenMMException("CustomGBForce does not support using multiple CUDA devices");
+    cutoff = force.getCutoffDistance();
     bool useExclusionsForValue = false;
     numComputedValues = force.getNumComputedValues();
     vector<string> computedValueNames(force.getNumComputedValues());
@@ -2956,7 +2955,7 @@ void CudaCalcCustomGBForceKernel::initialize(const System& system, const CustomG
             pairValueDefines["NEED_PADDING"] = "1";
         pairValueDefines["WARPS_PER_GROUP"] = cu.intToString(cu.getNonbondedUtilities().getForceThreadBlockSize()/CudaContext::TileSize);
         pairValueDefines["THREAD_BLOCK_SIZE"] = cu.intToString(cu.getNonbondedUtilities().getForceThreadBlockSize());
-        pairValueDefines["CUTOFF_SQUARED"] = cu.doubleToString(force.getCutoffDistance()*force.getCutoffDistance());
+        pairValueDefines["CUTOFF_SQUARED"] = cu.doubleToString(cutoff*cutoff);
         pairValueDefines["NUM_ATOMS"] = cu.intToString(cu.getNumAtoms());
         pairValueDefines["PADDED_NUM_ATOMS"] = cu.intToString(cu.getPaddedNumAtoms());
         pairValueDefines["NUM_BLOCKS"] = cu.intToString(cu.getNumAtomBlocks());
@@ -3123,7 +3122,7 @@ void CudaCalcCustomGBForceKernel::initialize(const System& system, const CustomG
             pairEnergyDefines["NEED_PADDING"] = "1";
         pairEnergyDefines["THREAD_BLOCK_SIZE"] = cu.intToString(cu.getNonbondedUtilities().getForceThreadBlockSize());
         pairEnergyDefines["WARPS_PER_GROUP"] = cu.intToString(cu.getNonbondedUtilities().getForceThreadBlockSize()/CudaContext::TileSize);
-        pairEnergyDefines["CUTOFF_SQUARED"] = cu.doubleToString(force.getCutoffDistance()*force.getCutoffDistance());
+        pairEnergyDefines["CUTOFF_SQUARED"] = cu.doubleToString(cutoff*cutoff);
         pairEnergyDefines["NUM_ATOMS"] = cu.intToString(cu.getNumAtoms());
         pairEnergyDefines["PADDED_NUM_ATOMS"] = cu.intToString(cu.getPaddedNumAtoms());
         pairEnergyDefines["NUM_BLOCKS"] = cu.intToString(cu.getNumAtomBlocks());
@@ -3367,7 +3366,7 @@ void CudaCalcCustomGBForceKernel::initialize(const System& system, const CustomG
             globals->upload(globalParamValues);
             arguments.push_back(CudaNonbondedUtilities::ParameterInfo(prefix+"globals", "float", 1, sizeof(float), globals->getDevicePointer()));
         }
-        cu.getNonbondedUtilities().addInteraction(useCutoff, usePeriodic, force.getNumExclusions() > 0, force.getCutoffDistance(), exclusionList, source, force.getForceGroup());
+        cu.getNonbondedUtilities().addInteraction(useCutoff, usePeriodic, force.getNumExclusions() > 0, cutoff, exclusionList, source, force.getForceGroup());
         for (int i = 0; i < (int) parameters.size(); i++)
             cu.getNonbondedUtilities().addParameter(parameters[i]);
         for (int i = 0; i < (int) arguments.size(); i++)
@@ -3393,7 +3392,7 @@ double CudaCalcCustomGBForceKernel::execute(ContextImpl& context, bool includeFo
             int endExclusionIndex = (cu.getContextIndex()+1)*numExclusionTiles/numContexts;
             pairValueDefines["FIRST_EXCLUSION_TILE"] = cu.intToString(startExclusionIndex);
             pairValueDefines["LAST_EXCLUSION_TILE"] = cu.intToString(endExclusionIndex);
-            pairValueDefines["CUTOFF"] = cu.doubleToString(nb.getCutoffDistance());
+            pairValueDefines["CUTOFF"] = cu.doubleToString(cutoff);
             CUmodule module = cu.createModule(CudaKernelSources::vectorOps+pairValueSrc, pairValueDefines);
             pairValueKernel = cu.getKernel(module, "computeN2Value");
             pairValueSrc = "";
@@ -3407,7 +3406,7 @@ double CudaCalcCustomGBForceKernel::execute(ContextImpl& context, bool includeFo
             int endExclusionIndex = (cu.getContextIndex()+1)*numExclusionTiles/numContexts;
             pairEnergyDefines["FIRST_EXCLUSION_TILE"] = cu.intToString(startExclusionIndex);
             pairEnergyDefines["LAST_EXCLUSION_TILE"] = cu.intToString(endExclusionIndex);
-            pairEnergyDefines["CUTOFF"] = cu.doubleToString(nb.getCutoffDistance());
+            pairEnergyDefines["CUTOFF"] = cu.doubleToString(cutoff);
             CUmodule module = cu.createModule(CudaKernelSources::vectorOps+pairEnergySrc, pairEnergyDefines);
             pairEnergyKernel = cu.getKernel(module, "computeN2Energy");
             pairEnergySrc = "";

platforms/cuda/src/CudaNonbondedUtilities.cpp

@@ -62,10 +62,10 @@ private:
     bool useDouble;
 };
 
-CudaNonbondedUtilities::CudaNonbondedUtilities(CudaContext& context) : context(context), cutoff(-1.0), useCutoff(false), usePeriodic(false), anyExclusions(false), usePadding(true),
+CudaNonbondedUtilities::CudaNonbondedUtilities(CudaContext& context) : context(context), useCutoff(false), usePeriodic(false), anyExclusions(false), usePadding(true),
         exclusionIndices(NULL), exclusionRowIndices(NULL), exclusionTiles(NULL), exclusions(NULL), interactingTiles(NULL), interactingAtoms(NULL),
         interactionCount(NULL), blockCenter(NULL), blockBoundingBox(NULL), sortedBlocks(NULL), sortedBlockCenter(NULL), sortedBlockBoundingBox(NULL),
-        oldPositions(NULL), rebuildNeighborList(NULL), blockSorter(NULL), nonbondedForceGroup(0), forceRebuildNeighborList(true) {
+        oldPositions(NULL), rebuildNeighborList(NULL), blockSorter(NULL), forceRebuildNeighborList(true), lastCutoff(0.0), groupFlags(0) {
     // Decide how many thread blocks to use.
 
     string errorMessage = "Error initializing nonbonded utilities";
@@ -109,24 +109,28 @@ CudaNonbondedUtilities::~CudaNonbondedUtilities() {
 }
 
 void CudaNonbondedUtilities::addInteraction(bool usesCutoff, bool usesPeriodic, bool usesExclusions, double cutoffDistance, const vector<vector<int> >& exclusionList, const string& kernel, int forceGroup) {
-    if (cutoff != -1.0) {
+    if (groupCutoff.size() > 0) {
         if (usesCutoff != useCutoff)
             throw OpenMMException("All Forces must agree on whether to use a cutoff");
         if (usesPeriodic != usePeriodic)
             throw OpenMMException("All Forces must agree on whether to use periodic boundary conditions");
-        if (cutoffDistance != cutoff)
-            throw OpenMMException("All Forces must use the same cutoff distance");
-        if (forceGroup != nonbondedForceGroup)
-            throw OpenMMException("All nonbonded forces must be in the same force group");
+        if (usesCutoff && groupCutoff.find(forceGroup) != groupCutoff.end() && groupCutoff[forceGroup] != cutoffDistance)
+            throw OpenMMException("All Forces in a single force group must use the same cutoff distance");
     }
     if (usesExclusions)
         requestExclusions(exclusionList);
     useCutoff = usesCutoff;
     usePeriodic = usesPeriodic;
-    cutoff = cutoffDistance;
-    if (kernel.size() > 0)
-        kernelSource += kernel+"\n";
-    nonbondedForceGroup = forceGroup;
+    groupCutoff[forceGroup] = cutoffDistance;
+    groupFlags |= 1<<forceGroup;
+    if (kernel.size() > 0) {
+        if (groupKernelSource.find(forceGroup) == groupKernelSource.end())
+            groupKernelSource[forceGroup] = "";
+        map<string, string> replacements;
+        replacements["CUTOFF"] = "CUTOFF_"+context.intToString(forceGroup);
+        replacements["CUTOFF_SQUARED"] = "CUTOFF_"+context.intToString(forceGroup)+"_SQUARED";
+        groupKernelSource[forceGroup] += context.replaceStrings(kernel, replacements)+"\n";
+    }
 }
 
 void CudaNonbondedUtilities::addParameter(const ParameterInfo& parameter) {
@@ -213,6 +217,9 @@ void CudaNonbondedUtilities::initialize(const System& system) {
         exclusionIndicesVec.insert(exclusionIndicesVec.end(), exclusionBlocksForBlock[i].begin(), exclusionBlocksForBlock[i].end());
         exclusionRowIndicesVec[i+1] = exclusionIndicesVec.size();
     }
+    maxExclusions = 0;
+    for (int i = 0; i < (int) exclusionBlocksForBlock.size(); i++)
+        maxExclusions = (maxExclusions > exclusionBlocksForBlock[i].size() ? maxExclusions : exclusionBlocksForBlock[i].size());
     exclusionIndices = CudaArray::create<unsigned int>(context, exclusionIndicesVec.size(), "exclusionIndices");
     exclusionRowIndices = CudaArray::create<unsigned int>(context, exclusionRowIndicesVec.size(), "exclusionRowIndices");
     exclusionIndices->upload(exclusionIndicesVec);
@@ -270,29 +277,33 @@ void CudaNonbondedUtilities::initialize(const System& system) {
         interactionCount->upload(count);
     }
 
-    // Create kernels.
+    // Record arguments for kernels.
 
-    if (kernelSource.size() > 0)
-        forceKernel = createInteractionKernel(kernelSource, parameters, arguments, true, true);
+    forceArgs.push_back(&context.getForce().getDevicePointer());
+    forceArgs.push_back(&context.getEnergyBuffer().getDevicePointer());
+    forceArgs.push_back(&context.getPosq().getDevicePointer());
+    forceArgs.push_back(&exclusions->getDevicePointer());
+    forceArgs.push_back(&exclusionTiles->getDevicePointer());
+    forceArgs.push_back(&startTileIndex);
+    forceArgs.push_back(&numTiles);
+    if (useCutoff) {
+        forceArgs.push_back(&interactingTiles->getDevicePointer());
+        forceArgs.push_back(&interactionCount->getDevicePointer());
+        forceArgs.push_back(context.getPeriodicBoxSizePointer());
+        forceArgs.push_back(context.getInvPeriodicBoxSizePointer());
+        forceArgs.push_back(context.getPeriodicBoxVecXPointer());
+        forceArgs.push_back(context.getPeriodicBoxVecYPointer());
+        forceArgs.push_back(context.getPeriodicBoxVecZPointer());
+        forceArgs.push_back(&maxTiles);
+        forceArgs.push_back(&blockCenter->getDevicePointer());
+        forceArgs.push_back(&blockBoundingBox->getDevicePointer());
+        forceArgs.push_back(&interactingAtoms->getDevicePointer());
+    }
+    for (int i = 0; i < (int) parameters.size(); i++)
+        forceArgs.push_back(&parameters[i].getMemory());
+    for (int i = 0; i < (int) arguments.size(); i++)
+        forceArgs.push_back(&arguments[i].getMemory());
     if (useCutoff) {
-        double padding = (usePadding ? 0.1*cutoff : 0.0);
-        double paddedCutoff = cutoff+padding;
-        map<string, string> defines;
-        defines["TILE_SIZE"] = context.intToString(CudaContext::TileSize);
-        defines["NUM_BLOCKS"] = context.intToString(context.getNumAtomBlocks());
-        defines["NUM_ATOMS"] = context.intToString(context.getNumAtoms());
-        defines["PADDING"] = context.doubleToString(padding);
-        defines["PADDED_CUTOFF"] = context.doubleToString(paddedCutoff);
-        defines["PADDED_CUTOFF_SQUARED"] = context.doubleToString(paddedCutoff*paddedCutoff);
-        defines["NUM_TILES_WITH_EXCLUSIONS"] = context.intToString(exclusionTiles->getSize());
-        if (usePeriodic)
-            defines["USE_PERIODIC"] = "1";
-        int maxExclusions = 0;
-        for (int i = 0; i < (int) exclusionBlocksForBlock.size(); i++)
-            maxExclusions = (maxExclusions > exclusionBlocksForBlock[i].size() ? maxExclusions : exclusionBlocksForBlock[i].size());
-        defines["MAX_EXCLUSIONS"] = context.intToString(maxExclusions);
-        CUmodule interactingBlocksProgram = context.createModule(CudaKernelSources::vectorOps+CudaKernelSources::findInteractingBlocks, defines);
-        findBlockBoundsKernel = context.getKernel(interactingBlocksProgram, "findBlockBounds");
         findBlockBoundsArgs.push_back(&numAtoms);
         findBlockBoundsArgs.push_back(context.getPeriodicBoxSizePointer());
         findBlockBoundsArgs.push_back(context.getInvPeriodicBoxSizePointer());
@@ -304,7 +315,6 @@ void CudaNonbondedUtilities::initialize(const System& system) {
         findBlockBoundsArgs.push_back(&blockBoundingBox->getDevicePointer());
         findBlockBoundsArgs.push_back(&rebuildNeighborList->getDevicePointer());
         findBlockBoundsArgs.push_back(&sortedBlocks->getDevicePointer());
-        sortBoxDataKernel = context.getKernel(interactingBlocksProgram, "sortBoxData");
         sortBoxDataArgs.push_back(&sortedBlocks->getDevicePointer());
         sortBoxDataArgs.push_back(&blockCenter->getDevicePointer());
         sortBoxDataArgs.push_back(&blockBoundingBox->getDevicePointer());
@@ -315,7 +325,6 @@ void CudaNonbondedUtilities::initialize(const System& system) {
         sortBoxDataArgs.push_back(&interactionCount->getDevicePointer());
         sortBoxDataArgs.push_back(&rebuildNeighborList->getDevicePointer());
         sortBoxDataArgs.push_back(&forceRebuildNeighborList);
-        findInteractingBlocksKernel = context.getKernel(interactingBlocksProgram, "findBlocksWithInteractions");
         findInteractingBlocksArgs.push_back(context.getPeriodicBoxSizePointer());
         findInteractingBlocksArgs.push_back(context.getInvPeriodicBoxSizePointer());
         findInteractingBlocksArgs.push_back(context.getPeriodicBoxVecXPointer());
@@ -338,30 +347,48 @@ void CudaNonbondedUtilities::initialize(const System& system) {
     }
 }
 
-void CudaNonbondedUtilities::prepareInteractions() {
+double CudaNonbondedUtilities::getMaxCutoffDistance() {
+    double cutoff = 0.0;
+    for (map<int, double>::const_iterator iter = groupCutoff.begin(); iter != groupCutoff.end(); ++iter)
+        cutoff = max(cutoff, iter->second);
+    return cutoff;
+}
+
+void CudaNonbondedUtilities::prepareInteractions(int forceGroups) {
+    if ((forceGroups&groupFlags) == 0)
+        return;
+    if (groupKernels.find(forceGroups) == groupKernels.end())
+        createKernelsForGroups(forceGroups);
     if (!useCutoff)
         return;
     if (numTiles == 0)
         return;
+    KernelSet& kernels = groupKernels[forceGroups];
     if (usePeriodic) {
         double4 box = context.getPeriodicBoxSize();
-        double minAllowedSize = 1.999999*cutoff;
+        double minAllowedSize = 1.999999*kernels.cutoffDistance;
         if (box.x < minAllowedSize || box.y < minAllowedSize || box.z < minAllowedSize)
             throw OpenMMException("The periodic box size has decreased to less than twice the nonbonded cutoff.");
     }
 
     // Compute the neighbor list.
 
-    context.executeKernel(findBlockBoundsKernel, &findBlockBoundsArgs[0], context.getNumAtoms());
+    if (lastCutoff != kernels.cutoffDistance)
+        forceRebuildNeighborList = true;
+    context.executeKernel(kernels.findBlockBoundsKernel, &findBlockBoundsArgs[0], context.getNumAtoms());
     blockSorter->sort(*sortedBlocks);
-    context.executeKernel(sortBoxDataKernel, &sortBoxDataArgs[0], context.getNumAtoms());
-    context.executeKernel(findInteractingBlocksKernel, &findInteractingBlocksArgs[0], context.getNumAtoms(), 256);
+    context.executeKernel(kernels.sortBoxDataKernel, &sortBoxDataArgs[0], context.getNumAtoms());
+    context.executeKernel(kernels.findInteractingBlocksKernel, &findInteractingBlocksArgs[0], context.getNumAtoms(), 256);
     forceRebuildNeighborList = false;
+    lastCutoff = kernels.cutoffDistance;
 }
 
-void CudaNonbondedUtilities::computeInteractions() {
-    if (kernelSource.size() > 0) {
-        context.executeKernel(forceKernel, &forceArgs[0], numForceThreadBlocks*forceThreadBlockSize, forceThreadBlockSize);
+void CudaNonbondedUtilities::computeInteractions(int forceGroups) {
+    if ((forceGroups&groupFlags) == 0)
+        return;
+    KernelSet& kernels = groupKernels[forceGroups];
+    if (kernels.hasForces) {
+        context.executeKernel(kernels.forceKernel, &forceArgs[0], numForceThreadBlocks*forceThreadBlockSize, forceThreadBlockSize);
         if (context.getComputeForceCount() == 1)
             updateNeighborListSize(); // This is the first time step, so check whether our initial guess was large enough.
     }
@@ -411,7 +438,43 @@ void CudaNonbondedUtilities::setAtomBlockRange(double startFraction, double endF
     forceRebuildNeighborList = true;
 }
 
-CUfunction CudaNonbondedUtilities::createInteractionKernel(const string& source, vector<ParameterInfo>& params, vector<ParameterInfo>& arguments, bool useExclusions, bool isSymmetric) {
+void CudaNonbondedUtilities::createKernelsForGroups(int groups) {
+    KernelSet kernels;
+    double cutoff = 0.0;
+    string source;
+    for (int i = 0; i < 32; i++) {
+        if ((groups&(1<<i)) != 0) {
+            cutoff = max(cutoff, groupCutoff[i]);
+            source += groupKernelSource[i];
+        }
+    }
+    kernels.hasForces = (source.size() > 0);
+    kernels.cutoffDistance = cutoff;
+    if (kernels.hasForces)
+        kernels.forceKernel = createInteractionKernel(source, parameters, arguments, true, true, groups);
+    if (useCutoff && kernels.hasForces) {
+        double padding = (usePadding ? 0.1*cutoff : 0.0);
+        double paddedCutoff = cutoff+padding;
+        map<string, string> defines;
+        defines["TILE_SIZE"] = context.intToString(CudaContext::TileSize);
+        defines["NUM_BLOCKS"] = context.intToString(context.getNumAtomBlocks());
+        defines["NUM_ATOMS"] = context.intToString(context.getNumAtoms());
+        defines["PADDING"] = context.doubleToString(padding);
+        defines["PADDED_CUTOFF"] = context.doubleToString(paddedCutoff);
+        defines["PADDED_CUTOFF_SQUARED"] = context.doubleToString(paddedCutoff*paddedCutoff);
+        defines["NUM_TILES_WITH_EXCLUSIONS"] = context.intToString(exclusionTiles->getSize());
+        if (usePeriodic)
+            defines["USE_PERIODIC"] = "1";
+        defines["MAX_EXCLUSIONS"] = context.intToString(maxExclusions);
+        CUmodule interactingBlocksProgram = context.createModule(CudaKernelSources::vectorOps+CudaKernelSources::findInteractingBlocks, defines);
+        kernels.findBlockBoundsKernel = context.getKernel(interactingBlocksProgram, "findBlockBounds");
+        kernels.sortBoxDataKernel = context.getKernel(interactingBlocksProgram, "sortBoxData");
+        kernels.findInteractingBlocksKernel = context.getKernel(interactingBlocksProgram, "findBlocksWithInteractions");
+    }
+    groupKernels[groups] = kernels;
+}
+
+CUfunction CudaNonbondedUtilities::createInteractionKernel(const string& source, vector<ParameterInfo>& params, vector<ParameterInfo>& arguments, bool useExclusions, bool isSymmetric, int groups) {
     map<string, string> replacements;
     replacements["COMPUTE_INTERACTION"] = source;
     const string suffixes[] = {"x", "y", "z", "w"};
@@ -588,8 +651,16 @@ CUfunction CudaNonbondedUtilities::createInteractionKernel(const string& source,
     if (useShuffle)
         defines["ENABLE_SHUFFLE"] = "1";
     defines["THREAD_BLOCK_SIZE"] = context.intToString(forceThreadBlockSize);
-    defines["CUTOFF_SQUARED"] = context.doubleToString(cutoff*cutoff);
-    defines["CUTOFF"] = context.doubleToString(cutoff);
+    double maxCutoff = 0.0;
+    for (int i = 0; i < 32; i++) {
+        if ((groups&(1<<i)) != 0) {
+            double cutoff = groupCutoff[i];
+            maxCutoff = max(maxCutoff, cutoff);
+            defines["CUTOFF_"+context.intToString(i)+"_SQUARED"] = context.doubleToString(cutoff*cutoff);
+            defines["CUTOFF_"+context.intToString(i)] = context.doubleToString(cutoff);
+        }
+    }
+    defines["MAX_CUTOFF"] = context.doubleToString(maxCutoff);
     defines["NUM_ATOMS"] = context.intToString(context.getNumAtoms());
     defines["PADDED_NUM_ATOMS"] = context.intToString(context.getPaddedNumAtoms());
     defines["NUM_BLOCKS"] = context.intToString(context.getNumAtomBlocks());
@@ -605,33 +676,5 @@ CUfunction CudaNonbondedUtilities::createInteractionKernel(const string& source,
         defines["PARAMETER_SIZE_IS_EVEN"] = "1";
     CUmodule program = context.createModule(CudaKernelSources::vectorOps+context.replaceStrings(CudaKernelSources::nonbonded, replacements), defines);
     CUfunction kernel = context.getKernel(program, "computeNonbonded");
-
-    // Set arguments to the Kernel.
-
-    int index = 0;
-    forceArgs.push_back(&context.getForce().getDevicePointer());
-    forceArgs.push_back(&context.getEnergyBuffer().getDevicePointer());
-    forceArgs.push_back(&context.getPosq().getDevicePointer());
-    forceArgs.push_back(&exclusions->getDevicePointer());
-    forceArgs.push_back(&exclusionTiles->getDevicePointer());
-    forceArgs.push_back(&startTileIndex);
-    forceArgs.push_back(&numTiles);
-    if (useCutoff) {
-        forceArgs.push_back(&interactingTiles->getDevicePointer());
-        forceArgs.push_back(&interactionCount->getDevicePointer());
-        forceArgs.push_back(context.getPeriodicBoxSizePointer());
-        forceArgs.push_back(context.getInvPeriodicBoxSizePointer());
-        forceArgs.push_back(context.getPeriodicBoxVecXPointer());
-        forceArgs.push_back(context.getPeriodicBoxVecYPointer());
-        forceArgs.push_back(context.getPeriodicBoxVecZPointer());
-        forceArgs.push_back(&maxTiles);
-        forceArgs.push_back(&blockCenter->getDevicePointer());
-        forceArgs.push_back(&blockBoundingBox->getDevicePointer());
-        forceArgs.push_back(&interactingAtoms->getDevicePointer());
-    }
-    for (int i = 0; i < (int) params.size(); i++)
-        forceArgs.push_back(&params[i].getMemory());
-    for (int i = 0; i < (int) arguments.size(); i++)
-        forceArgs.push_back(&arguments[i].getMemory());
     return kernel;
 }

platforms/cuda/src/kernels/nonbonded.cu

@@ -330,9 +330,9 @@ extern "C" __global__ void computeNonbonded(
         if (numTiles <= maxTiles) {
             x = tiles[pos];
             real4 blockSizeX = blockSize[x];
-            singlePeriodicCopy = (0.5f*periodicBoxSize.x-blockSizeX.x >= CUTOFF &&
-                                  0.5f*periodicBoxSize.y-blockSizeX.y >= CUTOFF &&
-                                  0.5f*periodicBoxSize.z-blockSizeX.z >= CUTOFF);
+            singlePeriodicCopy = (0.5f*periodicBoxSize.x-blockSizeX.x >= MAX_CUTOFF &&
+                                  0.5f*periodicBoxSize.y-blockSizeX.y >= MAX_CUTOFF &&
+                                  0.5f*periodicBoxSize.z-blockSizeX.z >= MAX_CUTOFF);
         }
         else
 #endif