TestCudaVerletIntegrator.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 Stanford University and the Authors.           *
 * Authors: Peter Eastman                                                     *
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/**
 * This tests the Cuda implementation of VerletIntegrator.
 */

#include "../../../tests/AssertionUtilities.h"
#include "OpenMMContext.h"
#include "CudaPlatform.h"
#include "HarmonicBondForce.h"
#include "NonbondedForce.h"
#include "System.h"
#include "VerletIntegrator.h"
#include "../src/SimTKUtilities/SimTKOpenMMRealType.h"
#include "../src/sfmt/SFMT.h"
#include <iostream>
#include <vector>

using namespace OpenMM;
using namespace std;

const double TOL = 1e-5;

void testSingleBond() {
    CudaPlatform platform;
    System system(2, 0);
    system.setParticleMass(0, 2.0);
    system.setParticleMass(1, 2.0);
    VerletIntegrator integrator(0.01);
    HarmonicBondForce* forceField = new HarmonicBondForce(1);
    forceField->setBondParameters(0, 0, 1, 1.5, 1);
    system.addForce(forceField);
    OpenMMContext context(system, integrator, platform);
    vector<Vec3> positions(2);
    positions[0] = Vec3(-1, 0, 0);
    positions[1] = Vec3(1, 0, 0);
    context.setPositions(positions);
    
    // This is simply a harmonic oscillator, so compare it to the analytical solution.
    
    const double freq = 1.0;;
    State state = context.getState(State::Energy);
    const double initialEnergy = state.getKineticEnergy()+state.getPotentialEnergy();
    for (int i = 0; i < 1000; ++i) {
        state = context.getState(State::Positions | State::Velocities | State::Energy);
        double time = state.getTime();
        double expectedDist = 1.5+0.5*std::cos(freq*time);
        ASSERT_EQUAL_VEC(Vec3(-0.5*expectedDist, 0, 0), state.getPositions()[0], 0.02);
        ASSERT_EQUAL_VEC(Vec3(0.5*expectedDist, 0, 0), state.getPositions()[1], 0.02);
        double expectedSpeed = -0.5*freq*std::sin(freq*time);
        ASSERT_EQUAL_VEC(Vec3(-0.5*expectedSpeed, 0, 0), state.getVelocities()[0], 0.02);
        ASSERT_EQUAL_VEC(Vec3(0.5*expectedSpeed, 0, 0), state.getVelocities()[1], 0.02);
        double energy = state.getKineticEnergy()+state.getPotentialEnergy();
        ASSERT_EQUAL_TOL(initialEnergy, energy, 0.01);
        integrator.step(1);
    }
}

void testConstraints() {
    const int numParticles = 8;
    const int numConstraints = numParticles/2;
    const double temp = 100.0;
    CudaPlatform platform;
    System system(numParticles, numConstraints);
    VerletIntegrator integrator(0.001);
    integrator.setConstraintTolerance(1e-5);
    NonbondedForce* forceField = new NonbondedForce(numParticles, 0);
    for (int i = 0; i < numParticles; ++i) {
        system.setParticleMass(i, 10.0);
        forceField->setParticleParameters(i, (i%2 == 0 ? 0.2 : -0.2), 0.5, 5.0);
    }
    for (int i = 0; i < numConstraints; ++i)
        system.setConstraintParameters(i, 2*i, 2*i+1, 1.0);
    system.addForce(forceField);
    OpenMMContext context(system, integrator, platform);
    vector<Vec3> positions(numParticles);
    vector<Vec3> velocities(numParticles);
    init_gen_rand(0);
    for (int i = 0; i < numParticles; ++i) {
        positions[i] = Vec3(i/2, (i+1)/2, 0);
        velocities[i] = Vec3(genrand_real2()-0.5, genrand_real2()-0.5, genrand_real2()-0.5);
    }
    context.setPositions(positions);
    context.setVelocities(velocities);
    
    // Simulate it and see whether the constraints remain satisfied.
    
    double initialEnergy = 0.0;
    for (int i = 0; i < 1000; ++i) {
        State state = context.getState(State::Positions | State::Energy);
            for (int j = 0; j < numConstraints; ++j) {
                int particle1, particle2;
                double distance;
                system.getConstraintParameters(j, particle1, particle2, distance);
                Vec3 p1 = state.getPositions()[particle1];
                Vec3 p2 = state.getPositions()[particle2];
                double dist = std::sqrt((p1[0]-p2[0])*(p1[0]-p2[0])+(p1[1]-p2[1])*(p1[1]-p2[1])+(p1[2]-p2[2])*(p1[2]-p2[2]));
                ASSERT_EQUAL_TOL(distance, dist, 2e-5);
            }
        double energy = state.getKineticEnergy()+state.getPotentialEnergy();
        if (i == 1)
            initialEnergy = energy;
        else if (i > 1)
            ASSERT_EQUAL_TOL(initialEnergy, energy, 0.05);
        integrator.step(1);
    }
}

int main() {
    try {
        testSingleBond();
        testConstraints();
    }
    catch(const exception& e) {
        cout << "exception: " << e.what() << endl;
        return 1;
    }
    cout << "Done" << endl;
    return 0;
}