TestReferenceCustomExternalForce.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 CustomExternalForce.
 */

#include "openmm/internal/AssertionUtilities.h"
#include "openmm/Context.h"
#include "ReferencePlatform.h"
#include "openmm/CustomExternalForce.h"
#include "openmm/System.h"
#include "openmm/VerletIntegrator.h"
#include "SimTKOpenMMRealType.h"
#include <iostream>
#include <vector>

using namespace OpenMM;
using namespace std;

ReferencePlatform platform;

const double TOL = 1e-5;

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);
    ASSERT(!forceField->usesPeriodicBoundaryConditions());
    ASSERT(!system.usesPeriodicBoundaryConditions());
    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);
    }
}

void testPeriodic() {
    Vec3 vx(5, 0, 0);
    Vec3 vy(0, 6, 0);
    Vec3 vz(1, 2, 7);
    double x0 = 51, y0 = -17, z0 = 11.2;
    System system;
    system.setDefaultPeriodicBoxVectors(vx, vy, vz);
    system.addParticle(1.0);
    CustomExternalForce* force = new CustomExternalForce("periodicdistance(x, y, z, x0, y0, z0)^2");
    force->addPerParticleParameter("x0");
    force->addPerParticleParameter("y0");
    force->addPerParticleParameter("z0");
    vector<double> params(3);
    params[0] = x0;
    params[1] = y0;
    params[2] = z0;
    force->addParticle(0, params);
    system.addForce(force);
    VerletIntegrator integrator(0.01);
    Context context(system, integrator, platform);
    vector<Vec3> positions(1);
    positions[0] = Vec3(0, 2, 0);
    context.setPositions(positions);
    for (int i = 0; i < 100; i++) {
        State state = context.getState(State::Positions | State::Forces | State::Energy);

        // Apply periodic boundary conditions to the difference between the two positions.

        Vec3 delta = Vec3(x0, y0, z0)-state.getPositions()[0];
        delta -= vz*floor(delta[2]/vz[2]+0.5);
        delta -= vy*floor(delta[1]/vy[1]+0.5);
        delta -= vx*floor(delta[0]/vx[0]+0.5);

        // Verify that the force and energy are correct.

        ASSERT_EQUAL_VEC(delta*2, state.getForces()[0], 1e-6);
        ASSERT_EQUAL_TOL(delta.dot(delta), state.getPotentialEnergy(), 1e-6);
        integrator.step(1);
    }
}

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