TestReferenceCustomTorsionForce.cpp

/* -------------------------------------------------------------------------- *
 *                                   OpenMM                                   *
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 * 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.               *
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 * Authors: Peter Eastman                                                     *
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/**
 * This tests the reference implementation of CustomTorsionForce.
 */

#include "../../../tests/AssertionUtilities.h"
#include "openmm/Context.h"
#include "ReferencePlatform.h"
#include "openmm/CustomTorsionForce.h"
#include "openmm/PeriodicTorsionForce.h"
#include "openmm/System.h"
#include "openmm/VerletIntegrator.h"
#include "sfmt/SFMT.h"
#include <iostream>
#include <vector>

using namespace OpenMM;
using namespace std;

const double TOL = 1e-5;

void testTorsions() {
    ReferencePlatform platform;

    // Create a system using a CustomTorsionForce.

    System customSystem;
    customSystem.addParticle(1.0);
    customSystem.addParticle(1.0);
    customSystem.addParticle(1.0);
    customSystem.addParticle(1.0);
    customSystem.addParticle(1.0);
    CustomTorsionForce* custom = new CustomTorsionForce("k*(1+cos(n*theta-theta0))");
    custom->addPerTorsionParameter("theta0");
    custom->addPerTorsionParameter("n");
    custom->addGlobalParameter("k", 0.5);
    vector<double> parameters(2);
    parameters[0] = 1.5;
    parameters[1] = 1;
    custom->addTorsion(0, 1, 2, 3, parameters);
    parameters[0] = 2.0;
    parameters[1] = 2;
    custom->addTorsion(1, 2, 3, 4, parameters);
    customSystem.addForce(custom);

    // Create an identical system using a PeriodicTorsionForce.

    System harmonicSystem;
    harmonicSystem.addParticle(1.0);
    harmonicSystem.addParticle(1.0);
    harmonicSystem.addParticle(1.0);
    harmonicSystem.addParticle(1.0);
    harmonicSystem.addParticle(1.0);
    VerletIntegrator integrator(0.01);
    PeriodicTorsionForce* periodic = new PeriodicTorsionForce();
    periodic->addTorsion(0, 1, 2, 3, 1, 1.5, 0.5);
    periodic->addTorsion(1, 2, 3, 4, 2, 2.0, 0.5);
    harmonicSystem.addForce(periodic);

    // Set the atoms in various positions, and verify that both systems give identical forces and energy.

    OpenMM_SFMT::SFMT sfmt;
    init_gen_rand(0, sfmt);

    vector<Vec3> positions(5);
    VerletIntegrator integrator1(0.01);
    VerletIntegrator integrator2(0.01);
    for (int i = 0; i < 10; i++) {
        Context c1(customSystem, integrator1, platform);
        Context c2(harmonicSystem, integrator2, platform);
        for (int j = 0; j < (int) positions.size(); j++)
            positions[j] = Vec3(5.0*genrand_real2(sfmt), 5.0*genrand_real2(sfmt), 5.0*genrand_real2(sfmt));
        c1.setPositions(positions);
        c2.setPositions(positions);
        State s1 = c1.getState(State::Forces | State::Energy);
        State s2 = c2.getState(State::Forces | State::Energy);
        for (int i = 0; i < customSystem.getNumParticles(); i++)
            ASSERT_EQUAL_VEC(s1.getForces()[i], s2.getForces()[i], TOL);
        ASSERT_EQUAL_TOL(s1.getPotentialEnergy(), s2.getPotentialEnergy(), TOL);
    }
}

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