void testForce() {
System system;
system.addParticle(1.0);
system.addParticle(1.0);
system.addParticle(1.0);
VerletIntegrator integrator(0.01);
CustomExternalForce* forceField = new CustomExternalForce("scale*(x+yscale*(y-y0)^2)");
forceField->addPerParticleParameter("y0");
forceField->addPerParticleParameter("yscale");
forceField->addGlobalParameter("scale", 0.5);
vector<double> parameters(2);
parameters[0] = 0.5;
parameters[1] = 2.0;
forceField->addParticle(0, parameters);
parameters[0] = 1.5;
parameters[1] = 3.0;
forceField->addParticle(2, parameters);
system.addForce(forceField);
Context context(system, integrator, platform);
vector<Vec3> positions(3);
positions[0] = Vec3(0, 2, 0);
positions[1] = Vec3(0, 0, 1);
positions[2] = Vec3(1, 0, 1);
context.setPositions(positions);
State state = context.getState(State::Forces | State::Energy);
{
const vector<Vec3>& forces = state.getForces();
ASSERT_EQUAL_VEC(Vec3(-0.5, -0.5*2.0*2.0*1.5, 0), forces[0], TOL);
ASSERT_EQUAL_VEC(Vec3(0, 0, 0), forces[1], TOL);
ASSERT_EQUAL_VEC(Vec3(-0.5, 0.5*3.0*2.0*1.5, 0), forces[2], TOL);
ASSERT_EQUAL_TOL(0.5*(1.0 + 2.0*1.5*1.5 + 3.0*1.5*1.5), state.getPotentialEnergy(), TOL);
}
// Try changing the parameters and make sure it's still correct.
parameters[0] = 1.4;
parameters[1] = 3.5;
forceField->setParticleParameters(1, 2, parameters);
forceField->updateParametersInContext(context);
state = context.getState(State::Forces | State::Energy);
{
const vector<Vec3>& forces = state.getForces();
ASSERT_EQUAL_VEC(Vec3(-0.5, -0.5*2.0*2.0*1.5, 0), forces[0], TOL);
ASSERT_EQUAL_VEC(Vec3(0, 0, 0), forces[1], TOL);
ASSERT_EQUAL_VEC(Vec3(-0.5, 0.5*3.5*2.0*1.4, 0), forces[2], TOL);
ASSERT_EQUAL_TOL(0.5*(1.0 + 2.0*1.5*1.5 + 3.5*1.4*1.4), state.getPotentialEnergy(), TOL);
}
}
