Fixed bug in switching functions with CustomNonbondedForce

platforms/cuda/src/CudaKernels.cpp

@@ -2271,7 +2271,7 @@ void CudaCalcCustomNonbondedForceKernel::initialize(const System& system, const
     Lepton::ParsedExpression energyExpression = Lepton::Parser::parse(force.getEnergyFunction(), functions).optimize();
     Lepton::ParsedExpression forceExpression = energyExpression.differentiate("r").optimize();
     map<string, Lepton::ParsedExpression> forceExpressions;
-    forceExpressions["tempEnergy += "] = energyExpression;
+    forceExpressions["real customEnergy = "] = energyExpression;
     forceExpressions["tempForce -= "] = forceExpression;
 
     // Create the kernels.

platforms/cuda/src/kernels/customNonbonded.cu

@@ -14,8 +14,10 @@ if (!isExcluded) {
 #endif
     COMPUTE_FORCE
 #if USE_SWITCH
-    tempForce = tempForce*switchValue - tempEnergy*switchDeriv;
-    tempEnergy *= switchValue;
+    tempForce = tempForce*switchValue - customEnergy*switchDeriv;
+    tempEnergy += customEnergy*switchValue;
+#else
+    tempEnergy += customEnergy;
 #endif
     dEdR += tempForce*invR;
 }

platforms/opencl/src/OpenCLKernels.cpp

@@ -2331,7 +2331,7 @@ void OpenCLCalcCustomNonbondedForceKernel::initialize(const System& system, cons
     Lepton::ParsedExpression energyExpression = Lepton::Parser::parse(force.getEnergyFunction(), functions).optimize();
     Lepton::ParsedExpression forceExpression = energyExpression.differentiate("r").optimize();
     map<string, Lepton::ParsedExpression> forceExpressions;
-    forceExpressions["tempEnergy += "] = energyExpression;
+    forceExpressions["real customEnergy = "] = energyExpression;
     forceExpressions["tempForce -= "] = forceExpression;
 
     // Create the kernels.

platforms/opencl/src/kernels/customNonbonded.cl

@@ -14,8 +14,10 @@ if (!isExcluded) {
 #endif
     COMPUTE_FORCE
 #if USE_SWITCH
-    tempForce = tempForce*switchValue - tempEnergy*switchDeriv;
-    tempEnergy *= switchValue;
+    tempForce = tempForce*switchValue - customEnergy*switchDeriv;
+    tempEnergy += customEnergy*switchValue;
+#else
+    tempEnergy += customEnergy;
 #endif
     dEdR += tempForce*invR;
 }

tests/TestCustomNonbondedForce.h

@@ -1034,6 +1034,65 @@ void testMultipleCutoffs() {
     }
 }
 
+void testMultipleSwitches() {
+    System system;
+    system.addParticle(1.0);
+    system.addParticle(1.0);
+    VerletIntegrator integrator(0.01);
+    
+    // Add multiple CustomNonbondedForces, one with a switching function and one without.
+    
+    CustomNonbondedForce* nonbonded1 = new CustomNonbondedForce("2*r");
+    nonbonded1->addParticle(vector<double>());
+    nonbonded1->addParticle(vector<double>());
+    nonbonded1->setNonbondedMethod(CustomNonbondedForce::CutoffNonPeriodic);
+    nonbonded1->setCutoffDistance(1.0);
+    system.addForce(nonbonded1);
+    CustomNonbondedForce* nonbonded2 = new CustomNonbondedForce("3*r");
+    nonbonded2->addParticle(vector<double>());
+    nonbonded2->addParticle(vector<double>());
+    nonbonded2->setNonbondedMethod(CustomNonbondedForce::CutoffNonPeriodic);
+    nonbonded2->setCutoffDistance(1.0);
+    nonbonded2->setSwitchingDistance(0.5);
+    nonbonded2->setUseSwitchingFunction(true);
+    nonbonded2->setForceGroup(1);
+    system.addForce(nonbonded2);
+    Context context(system, integrator, platform);
+    double r = 0.8;
+    vector<Vec3> positions(2);
+    positions[0] = Vec3(0, 0, 0);
+    positions[1] = Vec3(0, r, 0);
+    context.setPositions(positions);
+    double t = (r-0.5)/(1.0-0.5);
+    double switchValue = 1+t*t*t*(-10+t*(15-t*6));
+    double switchDeriv = t*t*(-30+t*(60-t*30))/(1.0-0.5);
+    double e1 = 2.0*r;
+    double e2 = 3.0*r*switchValue;
+    double f1 = 2.0;
+    double f2 = 3.0*switchValue + 3.0*switchDeriv*r;
+
+    // Check the first force.
+
+    State state = context.getState(State::Forces | State::Energy, false, 1);
+    ASSERT_EQUAL_VEC(Vec3(0, f1, 0), state.getForces()[0], TOL);
+    ASSERT_EQUAL_VEC(Vec3(0, -f1, 0), state.getForces()[1], TOL);
+    ASSERT_EQUAL_TOL(e1, state.getPotentialEnergy(), TOL);
+
+    // Check the second force.
+
+    state = context.getState(State::Forces | State::Energy, false, 2);
+    ASSERT_EQUAL_VEC(Vec3(0, f2, 0), state.getForces()[0], TOL);
+    ASSERT_EQUAL_VEC(Vec3(0, -f2, 0), state.getForces()[1], TOL);
+    ASSERT_EQUAL_TOL(e2, state.getPotentialEnergy(), TOL);
+
+    // Check the sum of both forces.
+
+    state = context.getState(State::Forces | State::Energy);
+    ASSERT_EQUAL_VEC(Vec3(0, f1+f2, 0), state.getForces()[0], TOL);
+    ASSERT_EQUAL_VEC(Vec3(0, -f1-f2, 0), state.getForces()[1], TOL);
+    ASSERT_EQUAL_TOL(e1+e2, state.getPotentialEnergy(), TOL);
+}
+
 void testIllegalVariable() {
     System system;
     system.addParticle(1.0);
@@ -1154,6 +1213,7 @@ int main(int argc, char* argv[]) {
         testInteractionGroupLongRangeCorrection();
         testInteractionGroupTabulatedFunction();
         testMultipleCutoffs();
+        testMultipleSwitches();
         testIllegalVariable();
         testEnergyParameterDerivatives();
         testEnergyParameterDerivatives2();