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#include "openmm/internal/MonteCarloFlexibleBarostatImpl.h"
#include "openmm/internal/ContextImpl.h"
#include "openmm/internal/OSRngSeed.h"
#include "openmm/Context.h"
#include "openmm/kernels.h"
#include "openmm/OpenMMException.h"
#include "SimTKOpenMMUtilities.h"
#include <cmath>
#include <vector>
#include <algorithm>

using namespace OpenMM;
using namespace std;

MonteCarloFlexibleBarostatImpl::MonteCarloFlexibleBarostatImpl(const MonteCarloFlexibleBarostat& owner) : owner(owner), step(0) {
}

void MonteCarloFlexibleBarostatImpl::initialize(ContextImpl& context) {
    if (!context.getSystem().usesPeriodicBoundaryConditions())
        throw OpenMMException("A barostat cannot be used with a non-periodic system");
    kernel = context.getPlatform().createKernel(ApplyMonteCarloBarostatKernel::Name(), context);
    kernel.getAs<ApplyMonteCarloBarostatKernel>().initialize(context.getSystem(), owner, 6, owner.getScaleMoleculesAsRigid());
    Vec3 box[3];
    context.getPeriodicBoxVectors(box[0], box[1], box[2]);
    double volume = box[0][0]*box[1][1]*box[2][2];
    lengthScale = 0.01*pow(volume, 1.0/3.0);
    numAttempted = 0;
    numAccepted = 0;
    SimTKOpenMMUtilities::setRandomNumberSeed(owner.getRandomNumberSeed());
}

void MonteCarloFlexibleBarostatImpl::updateContextState(ContextImpl& context, bool& forcesInvalid) {
    if (++step < owner.getFrequency() || owner.getFrequency() == 0)
        return;
    step = 0;

    // Compute the current potential energy.

    int groups = context.getIntegrator().getIntegrationForceGroups();
    double initialEnergy = context.getOwner().getState(State::Energy, false, groups).getPotentialEnergy();
    double pressure = context.getParameter(MonteCarloFlexibleBarostat::Pressure())*(AVOGADRO*1e-25);

    // Generate trial box vectors

    Vec3 box[3], trial[3];
    context.getPeriodicBoxVectors(box[0], box[1], box[2]);
    trial[0][0] = box[0][0] + lengthScale*2*(SimTKOpenMMUtilities::getUniformlyDistributedRandomNumber()-0.5);
    trial[1][0] = box[1][0] + lengthScale*2*(SimTKOpenMMUtilities::getUniformlyDistributedRandomNumber()-0.5);
    trial[1][1] = box[1][1] + lengthScale*2*(SimTKOpenMMUtilities::getUniformlyDistributedRandomNumber()-0.5);
    trial[2][0] = box[2][0] + lengthScale*2*(SimTKOpenMMUtilities::getUniformlyDistributedRandomNumber()-0.5);
    trial[2][1] = box[2][1] + lengthScale*2*(SimTKOpenMMUtilities::getUniformlyDistributedRandomNumber()-0.5);
    trial[2][2] = box[2][2] + lengthScale*2*(SimTKOpenMMUtilities::getUniformlyDistributedRandomNumber()-0.5);

    // Recompute reduced form by flipping/linear combinations.

    for (auto i = 0; i < 3; i++)
        if (trial[i][i] < 0)
            trial[i] = -trial[i];
    trial[2] -= trial[1]*round(trial[2][1]/trial[1][1]);
    trial[2] -= trial[0]*round(trial[2][0]/trial[0][0]);
    trial[1] -= trial[0]*round(trial[1][0]/trial[0][0]);
    double volume = box[0][0]*box[1][1]*box[2][2];
    double newVolume = trial[0][0]*trial[1][1]*trial[2][2];

    // Scale particle coordinates and update box vectors in context.

    kernel.getAs<ApplyMonteCarloBarostatKernel>().saveCoordinates(context);
    context.getOwner().setPeriodicBoxVectors(trial[0], trial[1], trial[2]);
    kernel.getAs<ApplyMonteCarloBarostatKernel>().scaleCoordinates(context, trial[0][0]/box[0][0], trial[1][1]/box[1][1], trial[2][2]/box[2][2]);

    // Compute the energy of the modified system.

    double numberOfScaledParticles;
    if (owner.getScaleMoleculesAsRigid())
        numberOfScaledParticles = context.getMolecules().size();
    else
        numberOfScaledParticles = context.getSystem().getNumParticles();
    double finalEnergy = context.getOwner().getState(State::Energy, false, groups).getPotentialEnergy();
    double kT = BOLTZ*context.getParameter(MonteCarloFlexibleBarostat::Temperature());
    double w0 = finalEnergy-initialEnergy;
    double w1 = pressure*(newVolume-volume);
    double w2 = -(numberOfScaledParticles-2)*kT*log(newVolume/volume);
    double w3 = -kT*log((trial[0][0]*trial[0][0]*trial[1][1])/(box[0][0]*box[0][0]*box[1][1]));
    double w  = w0+w1+w2+w3;
    if (w > 0 && SimTKOpenMMUtilities::getUniformlyDistributedRandomNumber() > exp(-w/kT)) {
        // Reject the step.

        context.getOwner().setPeriodicBoxVectors(box[0], box[1], box[2]);
        kernel.getAs<ApplyMonteCarloBarostatKernel>().restoreCoordinates(context);
    }
    else {
        numAccepted++;
        forcesInvalid = true;
    }
    numAttempted++;
    if (numAttempted >= 10) {
        if (numAccepted < 0.25*numAttempted) {
            lengthScale /= 1.1;
            numAttempted = 0;
            numAccepted = 0;
        }
        else if (numAccepted > 0.75*numAttempted) {
            lengthScale = min(lengthScale*1.1, pow(newVolume, 1.0/3.0)*0.3);
            numAttempted = 0;
            numAccepted = 0;
        }
    }

}

map<string, double> MonteCarloFlexibleBarostatImpl::getDefaultParameters() {
    return {{MonteCarloFlexibleBarostat::Pressure(), getOwner().getDefaultPressure()},
            {MonteCarloFlexibleBarostat::Temperature(), getOwner().getDefaultTemperature()}};
}

vector<string> MonteCarloFlexibleBarostatImpl::getKernelNames() {
    return {ApplyMonteCarloBarostatKernel::Name()};
}

void MonteCarloFlexibleBarostatImpl::computeCurrentPressure(ContextImpl& context, vector<double>& pressure) {
    pressure.resize(6);
    Vec3 box[3];
    context.getPeriodicBoxVectors(box[0], box[1], box[2]);
    double volume = box[0][0]*box[1][1]*box[2][2];
    double delta = 1e-3;
    kernel.getAs<ApplyMonteCarloBarostatKernel>().saveCoordinates(context);
    vector<double> ke;
    kernel.getAs<ApplyMonteCarloBarostatKernel>().computeKineticEnergy(context, ke);

    // Compute each component of the pressure tensor.

    for (int component = 0; component < 6; component++)
        pressure[component] = (2.0*ke[component] - computePressureComponent(context, delta, component))/(volume*AVOGADRO*1e-25);

    // Restore the context to its original state.

    kernel.getAs<ApplyMonteCarloBarostatKernel>().restoreCoordinates(context);
}

double MonteCarloFlexibleBarostatImpl::computePressureComponent(ContextImpl& context, double delta, int component) {
    Vec3 box[3], newBox[3];
    context.getPeriodicBoxVectors(box[0], box[1], box[2]);
    newBox[0] = box[0];
    newBox[1] = box[1];
    newBox[2] = box[2];
    int scaleVec, scaleComponent;
    if (component < 3)
        scaleVec = scaleComponent = component;
    else if (component == 3) {
        scaleVec = 1;
        scaleComponent = 0;
    }
    else if (component == 4) {
        scaleVec = 2;
        scaleComponent = 0;
    }
    else if (component == 5) {
        scaleVec = 2;
        scaleComponent = 1;
    }
    else
        throw OpenMMException("Illegal component index");
    int groups = context.getIntegrator().getIntegrationForceGroups();

    // Compute the first energy.

    Vec3 scale(1, 1, 1);
    if (component < 3) {
        scale[component] = 1.0+delta;
        kernel.getAs<ApplyMonteCarloBarostatKernel>().scaleCoordinates(context, scale[0], scale[1], scale[2]);
    }
    newBox[scaleVec][scaleComponent] *= 1.0+delta;
    setBoxVectors(context, newBox[0], newBox[1], newBox[2]);
    double energy1 = context.getOwner().getState(State::Energy, false, groups).getPotentialEnergy();

    // Compute the second energy.

    if (component < 3) {
        scale[component] = (1.0-delta)/(1.0+delta);
        kernel.getAs<ApplyMonteCarloBarostatKernel>().scaleCoordinates(context, scale[0], scale[1], scale[2]);
    }
    newBox[scaleVec][scaleComponent] = box[scaleVec][scaleComponent]*(1.0-delta);
    setBoxVectors(context, newBox[0], newBox[1], newBox[2]);
    double energy2 = context.getOwner().getState(State::Energy, false, groups).getPotentialEnergy();

    // Reset the box shape.

    if (component < 3) {
        scale[component] = 1.0/(1.0-delta);
        kernel.getAs<ApplyMonteCarloBarostatKernel>().scaleCoordinates(context, scale[0], scale[1], scale[2]);
    }
    context.getOwner().setPeriodicBoxVectors(box[0], box[1], box[2]);

    // Compute the potential energy contribution to this element of the pressure tensor.

    double volume = box[0][0]*box[1][1]*box[2][2];
    return (energy2-energy1)/(volume*2*delta);
}

void MonteCarloFlexibleBarostatImpl::setBoxVectors(ContextImpl& context, Vec3 a, Vec3 b, Vec3 c) {
    // Convert the box vectors to reduced form.

    c = c - b*round(c[1]/b[1]);
    c = c - a*round(c[0]/a[0]);
    b = b - a*round(b[0]/a[0]);
    context.getOwner().setPeriodicBoxVectors(a, b, c);
}