Fixed CustomExternalForce::usesPeriodicBoundaryConditions()

openmmapi/include/openmm/CustomExternalForce.h

@@ -214,9 +214,7 @@ public:
      *
      * @returns false
      */
-    bool usesPeriodicBoundaryConditions() const {
-        return false;
-    }
+    bool usesPeriodicBoundaryConditions() const;
 protected:
     ForceImpl* createImpl() const;
 private:

openmmapi/src/CustomExternalForce.cpp

@@ -119,3 +119,7 @@ ForceImpl* CustomExternalForce::createImpl() const {
 void CustomExternalForce::updateParametersInContext(Context& context) {
     dynamic_cast<CustomExternalForceImpl&>(getImplInContext(context)).updateParametersInContext(getContextImpl(context));
 }
+
+bool CustomExternalForce::usesPeriodicBoundaryConditions() const {
+    return (energyExpression.find("periodicdistance") != string::npos);
+}

platforms/reference/tests/TestReferenceCustomExternalForce.cpp

@@ -119,6 +119,8 @@ void testPeriodic() {
     params[2] = z0;
     force->addParticle(0, params);
     system.addForce(force);
+    ASSERT(force->usesPeriodicBoundaryConditions());
+    ASSERT(system.usesPeriodicBoundaryConditions());
     VerletIntegrator integrator(0.01);
     Context context(system, integrator, platform);
     vector<Vec3> positions(1);