TestCudaCMMotionRemover.cpp

/* -------------------------------------------------------------------------- *
 *                                   OpenMM                                   *
 * -------------------------------------------------------------------------- *
 * This is part of the OpenMM molecular simulation toolkit originating from   *
 * Simbios, the NIH National Center for Physics-Based Simulation of           *
 * Biological Structures at Stanford, funded under the NIH Roadmap for        *
 * Medical Research, grant U54 GM072970. See https://simtk.org.               *
 *                                                                            *
 * Portions copyright (c) 2008-2012 Stanford University and the Authors.      *
 * Authors: Peter Eastman                                                     *
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/**
 * This tests the CUDA implementation of AndersenThermostat.
 */

#include "openmm/internal/AssertionUtilities.h"
#include "openmm/CMMotionRemover.h"
#include "openmm/Context.h"
#include "CudaPlatform.h"
#include "openmm/HarmonicBondForce.h"
#include "openmm/NonbondedForce.h"
#include "openmm/System.h"
#include "openmm/LangevinIntegrator.h"
#include "openmm/VerletIntegrator.h"
#include "../src/SimTKUtilities/SimTKOpenMMRealType.h"
#include "sfmt/SFMT.h"
#include <iostream>
#include <vector>

using namespace OpenMM;
using namespace std;

Vec3 calcCM(const vector<Vec3>& values, System& system) {
    Vec3 cm;
    for (int j = 0; j < system.getNumParticles(); ++j) {
        cm[0] += values[j][0]*system.getParticleMass(j);
        cm[1] += values[j][1]*system.getParticleMass(j);
        cm[2] += values[j][2]*system.getParticleMass(j);
    }
    return cm;
}

void testMotionRemoval(Integrator& integrator) {
    const int numParticles = 8;
    CudaPlatform platform;
    System system;
    HarmonicBondForce* bonds = new HarmonicBondForce();
    bonds->addBond(2, 3, 2.0, 0.5);
    system.addForce(bonds);
    NonbondedForce* nonbonded = new NonbondedForce();
    for (int i = 0; i < numParticles; ++i) {
        system.addParticle(i+1);
        nonbonded->addParticle((i%2 == 0 ? 1.0 : -1.0), 1.0, 5.0);
    }
    system.addForce(nonbonded);
    CMMotionRemover* remover = new CMMotionRemover();
    system.addForce(remover);
    Context context(system, integrator, platform);
    vector<Vec3> positions(numParticles);
    vector<Vec3> velocities(numParticles);
    OpenMM_SFMT::SFMT sfmt;
    init_gen_rand(0, sfmt);

    for (int i = 0; i < numParticles; ++i) {
        positions[i] = Vec3((i%2 == 0 ? 2 : -2), (i%4 < 2 ? 2 : -2), (i < 4 ? 2 : -2));
        velocities[i] = Vec3(genrand_real2(sfmt)-0.5, genrand_real2(sfmt)-0.5, genrand_real2(sfmt)-0.5);
    }
    context.setPositions(positions);
    context.setVelocities(velocities);

    // Now run it for a while and see if the center of mass remains fixed.

    Vec3 cmPos = calcCM(context.getState(State::Positions).getPositions(), system);
    for (int i = 0; i < 1000; ++i) {
        integrator.step(1);
        State state = context.getState(State::Positions | State::Velocities);
        Vec3 pos = calcCM(state.getPositions(), system);
        ASSERT_EQUAL_VEC(cmPos, pos, 1e-2);
        Vec3 vel = calcCM(state.getVelocities(), system);
        if (i > 0) {
            ASSERT_EQUAL_VEC(Vec3(0, 0, 0), vel, 1e-2);
        }
    }
}

int main() {
    try {
        LangevinIntegrator langevin(0.0, 1e-5, 0.01);
        testMotionRemoval(langevin);
        VerletIntegrator verlet(0.01);
        testMotionRemoval(verlet);
    }
    catch(const exception& e) {
        cout << "exception: " << e.what() << endl;
        return 1;
    }
    cout << "Done" << endl;
    return 0;
}