Attempt to apply KE computation optimization and corresponding fix from #2524

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());