// Copyright (c) 2009-2021 The Regents of the University of Michigan
// This file is part of the HOOMD-blue project, released under the BSD 3-Clause License.


// this include is necessary to get MPI included before anything else to support intel MPI
#include "hoomd/ExecutionConfiguration.h"

#include <iostream>

#include <functional>

#include "hoomd/md/HarmonicDihedralForceCompute.h"
#include "hoomd/ConstForceCompute.h"
#ifdef ENABLE_HIP
#include "hoomd/md/HarmonicDihedralForceComputeGPU.h"
#endif

#include <stdio.h>

#include "hoomd/Initializers.h"
#include "hoomd/SnapshotSystemData.h"

using namespace std;
using namespace std::placeholders;

#include "hoomd/test/upp11_config.h"
HOOMD_UP_MAIN();

//! Typedef to make using the std::function factory easier
typedef std::function<std::shared_ptr<HarmonicDihedralForceCompute>  (std::shared_ptr<SystemDefinition> sysdef)> dihedralforce_creator;

//! Perform some simple functionality tests of any BondForceCompute
void dihedral_force_basic_tests(dihedralforce_creator tf_creator, std::shared_ptr<ExecutionConfiguration> exec_conf)
    {
    /////////////////////////////////////////////////////////
    // start with the simplest possible test: 4 particles in a huge box with only one dihedral type !!!! NO DIHEDRALS
    std::shared_ptr<SystemDefinition> sysdef_4(new SystemDefinition(4, BoxDim(1000.0), 1, 0, 0, 1, 0, exec_conf));
    std::shared_ptr<ParticleData> pdata_4 = sysdef_4->getParticleData();

    pdata_4->setPosition(0,make_scalar3(10.0,1.0,2.0));
    pdata_4->setPosition(1,make_scalar3(1.0,1.0,1.0));
    pdata_4->setPosition(2,make_scalar3(6.0,-7.0,8.0));
    pdata_4->setPosition(3,make_scalar3(9.0,50.0,11.0));

    /*
        printf(" Particle 1: x = %f  y = %f  z = %f \n", h_pos.data[0].x, h_pos.data[0].y, h_pos.data[0].z);
        printf(" Particle 2: x = %f  y = %f  z = %f \n", h_pos.data[1].x, h_pos.data[1].y, h_pos.data[1].z);
        printf(" Particle 3: x = %f  y = %f  z = %f \n", h_pos.data[2].x, h_pos.data[2].y, h_pos.data[2].z);
        printf(" Particle 4: x = %f  y = %f  z = %f \n", h_pos.data[3].x, h_pos.data[3].y, h_pos.data[3].z);
        printf("\n");
    */

    // create the dihedral force compute to check
    std::shared_ptr<HarmonicDihedralForceCompute> fc_4 = tf_creator(sysdef_4);
    fc_4->setParams(0, Scalar(30.0), -1, 3, Scalar(0)); // type=0, K=30.0,sign=-1,multiplicity=3, phaseoffset=0

    // compute the force and check the results
    fc_4->compute(0);

    {
    GlobalArray<Scalar4>& force_array_1 =  fc_4->getForceArray();
    GlobalArray<Scalar>& virial_array_1 =  fc_4->getVirialArray();
    size_t pitch = 0;
    ArrayHandle<Scalar4> h_force_1(force_array_1,access_location::host,access_mode::read);
    ArrayHandle<Scalar> h_virial_1(virial_array_1,access_location::host,access_mode::read);

    // check that the force is correct, it should be 0 since we haven't created any dihedrals yet
    MY_CHECK_SMALL(h_force_1.data[0].x, tol);
    MY_CHECK_SMALL(h_force_1.data[0].y, tol);
    MY_CHECK_SMALL(h_force_1.data[0].z, tol);
    MY_CHECK_SMALL(h_force_1.data[0].w, tol);
    MY_CHECK_SMALL(h_virial_1.data[0*pitch], tol);
    MY_CHECK_SMALL(h_virial_1.data[1*pitch], tol);
    MY_CHECK_SMALL(h_virial_1.data[2*pitch], tol);
    MY_CHECK_SMALL(h_virial_1.data[3*pitch], tol);
    MY_CHECK_SMALL(h_virial_1.data[4*pitch], tol);
    MY_CHECK_SMALL(h_virial_1.data[5*pitch], tol);
    }

    // add an dihedrals and check again
    sysdef_4->getDihedralData()->addBondedGroup(Dihedral(0,0,1,2,3)); // add type 0 dihedral between atoms 0-1-2-3
    fc_4->compute(1);

    {
    // this time there should be a force
    GlobalArray<Scalar4>& force_array_2 =  fc_4->getForceArray();
    GlobalArray<Scalar>& virial_array_2 =  fc_4->getVirialArray();
    size_t pitch = virial_array_2.getPitch();
    ArrayHandle<Scalar4> h_force_2(force_array_2,access_location::host,access_mode::read);
    ArrayHandle<Scalar> h_virial_2(virial_array_2,access_location::host,access_mode::read);
    MY_CHECK_CLOSE(h_force_2.data[0].x, -0.5*0.118121, tol);
    MY_CHECK_CLOSE(h_force_2.data[0].y, 0.5*0.856380, tol);
    MY_CHECK_CLOSE(h_force_2.data[0].z, 0.5*1.063092, tol);
    MY_CHECK_CLOSE(h_force_2.data[0].w, 0.5*14.945559, tol);
    MY_CHECK_SMALL(h_virial_2.data[0*pitch+0]
                        +h_virial_2.data[3*pitch+0]
                        +h_virial_2.data[5*pitch+0], tol);

    MY_CHECK_CLOSE(h_force_2.data[1].x, -0.5*0.522868, tol);
    MY_CHECK_CLOSE(h_force_2.data[1].y, -0.5*0.525225, tol);
    MY_CHECK_CLOSE(h_force_2.data[1].z, -0.5*0.226780, tol);
    MY_CHECK_CLOSE(h_force_2.data[1].w, 0.5*14.945559, tol);
    MY_CHECK_SMALL(h_virial_2.data[0*pitch+1]
                        +h_virial_2.data[3*pitch+1]
                        +h_virial_2.data[5*pitch+1], tol);

    MY_CHECK_CLOSE(h_force_2.data[2].x, 0.5*0.445003, tol);
    MY_CHECK_CLOSE(h_force_2.data[2].y, -0.5*0.328375, tol);
    MY_CHECK_CLOSE(h_force_2.data[2].z, -0.5*0.693145, tol);
    MY_CHECK_CLOSE(h_force_2.data[2].w, 0.5*14.945559, tol);
    MY_CHECK_SMALL(h_virial_2.data[0*pitch+2]
                        +h_virial_2.data[3*pitch+2]
                        +h_virial_2.data[5*pitch+2], tol);

    MY_CHECK_CLOSE(h_force_2.data[3].x, 0.5*0.195986, tol);
    MY_CHECK_CLOSE(h_force_2.data[3].y, -0.5*0.002780, loose_tol);
    MY_CHECK_CLOSE(h_force_2.data[3].z, -0.5*0.143167, tol);
    MY_CHECK_CLOSE(h_force_2.data[3].w, 0.5*14.945559, tol);
    MY_CHECK_SMALL(h_virial_2.data[0*pitch+3]
                        +h_virial_2.data[3*pitch+3]
                        +h_virial_2.data[5*pitch+3], tol);
    }

    /*
     FORCE 1: fx = -0.118121  fy = 0.856380  fz = 1.063092
     FORCE 2: fx = -0.522868  fy = -0.525225  fz = -0.226780
     FORCE 3: fx = 0.445003  fy = -0.328375  fz = -0.693145
     FORCE 4: fx = 0.195986  fy = -0.002780  fz = -0.143167

    */

    // rearrange the two particles in memory and see if they are properly updated
    {
    ArrayHandle<Scalar4> h_pos(pdata_4->getPositions(), access_location::host, access_mode::readwrite);
    ArrayHandle<unsigned int> h_tag(pdata_4->getTags(), access_location::host, access_mode::readwrite);
    ArrayHandle<unsigned int> h_rtag(pdata_4->getRTags(), access_location::host, access_mode::readwrite);

    h_pos.data[1].x = Scalar(10.0); // put atom b at (10,1,2)
    h_pos.data[1].y = Scalar(1.0);
    h_pos.data[1].z = Scalar(2.0);

    h_pos.data[0].x = h_pos.data[0].y = h_pos.data[0].z = Scalar(1.0); // put atom a at (1,1,1)

    h_tag.data[0] = 1;
    h_tag.data[1] = 0;
    h_rtag.data[0] = 1;
    h_rtag.data[1] = 0;
    }

    // notify that we made the sort
    pdata_4->notifyParticleSort();
    // recompute at the same timestep, the forces should still be updated
    fc_4->compute(1);

    {
    GlobalArray<Scalar4>& force_array_3 =  fc_4->getForceArray();
    GlobalArray<Scalar>& virial_array_3 =  fc_4->getVirialArray();
    size_t pitch = virial_array_3.getPitch();
    ArrayHandle<Scalar4> h_force_3(force_array_3,access_location::host,access_mode::read);
    ArrayHandle<Scalar> h_virial_3(virial_array_3,access_location::host,access_mode::read);

    MY_CHECK_CLOSE(h_force_3.data[1].x, -0.5*0.118121, tol);
    MY_CHECK_CLOSE(h_force_3.data[1].y, 0.5*0.856380, tol);
    MY_CHECK_CLOSE(h_force_3.data[1].z, 0.5*1.063092, tol);
    MY_CHECK_CLOSE(h_force_3.data[1].w, 0.5*14.945559, tol);
    MY_CHECK_SMALL(h_virial_3.data[0*pitch+1]
                        +h_virial_3.data[3*pitch+1]
                        +h_virial_3.data[5*pitch+1], tol);

    MY_CHECK_CLOSE(h_force_3.data[0].x, -0.5*0.522868, tol);
    MY_CHECK_CLOSE(h_force_3.data[0].y, -0.5*0.525225, tol);
    MY_CHECK_CLOSE(h_force_3.data[0].z, -0.5*0.226780, tol);
    MY_CHECK_CLOSE(h_force_3.data[0].w, 0.5*14.945559, tol);
    MY_CHECK_SMALL(h_virial_3.data[0*pitch+0]
                        +h_virial_3.data[3*pitch+0]
                        +h_virial_3.data[5*pitch+0], tol);
    }

    ////////////////////////////////////////////////////////////////////
    // now, lets do a more thorough test and include boundary conditions
    // there are way too many permutations to test here, so I will simply
    // test +x, -x, +y, -y, +z, and -z independently
    // build a 8 particle system with particles across each boundary
    // also test more than one type of dihedral
    std::shared_ptr<SystemDefinition> sysdef_8(new SystemDefinition(8, BoxDim(60.0, 70.0, 80.0), 1, 0, 0, 2, 0, exec_conf));
    std::shared_ptr<ParticleData> pdata_8 = sysdef_8->getParticleData();

    {
    ArrayHandle<Scalar4> h_pos(pdata_8->getPositions(), access_location::host, access_mode::readwrite);

    h_pos.data[0].x = Scalar(-9.6); h_pos.data[0].y = -9.0; h_pos.data[0].z = 0.0;
    h_pos.data[1].x =  Scalar(9.6); h_pos.data[1].y = 1.0; h_pos.data[1].z = 0.0;
    h_pos.data[2].x = 0; h_pos.data[2].y = Scalar(-19.6); h_pos.data[2].z = 0.0;
    h_pos.data[3].x = 0; h_pos.data[3].y = Scalar(19.6); h_pos.data[3].z = 10.0;
    h_pos.data[4].x = 0; h_pos.data[4].y = 0; h_pos.data[4].z = Scalar(-29.6);
    h_pos.data[5].x = 0; h_pos.data[5].y = 0; h_pos.data[5].z =  Scalar(29.6);
    h_pos.data[6].x = 3; h_pos.data[6].y = 3; h_pos.data[6].z =  Scalar(29.6);
    h_pos.data[7].x = 3; h_pos.data[7].y = 0; h_pos.data[7].z =  Scalar(31.0);
    }

    std::shared_ptr<HarmonicDihedralForceCompute> fc_8 = tf_creator(sysdef_8);
    fc_8->setParams(0, 50.0, -1, 3, 0.0);
    fc_8->setParams(1, 30.0,  1, 4, 0.0);

    sysdef_8->getDihedralData()->addBondedGroup(Dihedral(0, 0,1,2,3));
    sysdef_8->getDihedralData()->addBondedGroup(Dihedral(1, 4,5,6,7));

    fc_8->compute(0);

    {
    // check that the forces are correctly computed
    GlobalArray<Scalar4>& force_array_4 =  fc_8->getForceArray();
    GlobalArray<Scalar>& virial_array_4 =  fc_8->getVirialArray();
    size_t pitch = virial_array_4.getPitch();
    ArrayHandle<Scalar4> h_force_4(force_array_4,access_location::host,access_mode::read);
    ArrayHandle<Scalar> h_virial_4(virial_array_4,access_location::host,access_mode::read);

    MY_CHECK_SMALL(h_force_4.data[0].x, tol);
    MY_CHECK_SMALL(h_force_4.data[0].y, tol);
    MY_CHECK_CLOSE(h_force_4.data[0].z, 0.5*10.504562,tol);
    MY_CHECK_CLOSE(h_force_4.data[0].w, 0.5*7.687906, tol);
    MY_CHECK_SMALL(h_virial_4.data[0*pitch+0]
                        +h_virial_4.data[3*pitch+0]
                        +h_virial_4.data[5*pitch+0], tol);

    MY_CHECK_CLOSE(h_force_4.data[1].x, -0.5*5.724548, tol);
    MY_CHECK_CLOSE(h_force_4.data[1].y, 0.5*2.667751,tol);
    MY_CHECK_CLOSE(h_force_4.data[1].z, 0.5*5.650116,tol); // 5.650116
    MY_CHECK_CLOSE(h_force_4.data[1].w, 0.5*7.687906, tol);
    MY_CHECK_SMALL(h_virial_4.data[0*pitch+1]
                        +h_virial_4.data[3*pitch+1]
                        +h_virial_4.data[5*pitch+1], tol);

    MY_CHECK_CLOSE(h_force_4.data[2].x, 0.5*10.384811,tol);
    MY_CHECK_CLOSE(h_force_4.data[2].y, -0.5*4.839524, tol);
    MY_CHECK_CLOSE(h_force_4.data[2].z, -0.5*22.843740,tol); //
    MY_CHECK_CLOSE(h_force_4.data[2].w, 0.5*7.687906, tol);
    MY_CHECK_SMALL(h_virial_4.data[0*pitch+2]
                        +h_virial_4.data[3*pitch+2]
                        +h_virial_4.data[5*pitch+2], tol);

    MY_CHECK_CLOSE(h_force_4.data[3].x, -0.5*4.660264,tol);
    MY_CHECK_CLOSE(h_force_4.data[3].y, 0.5*2.171773, tol);
    MY_CHECK_CLOSE(h_force_4.data[3].z, 0.5*6.689062,tol); //
    MY_CHECK_CLOSE(h_force_4.data[3].w, 0.5*7.687906, tol);
    MY_CHECK_SMALL(h_virial_4.data[0*pitch+3]
                        +h_virial_4.data[3*pitch+3]
                        +h_virial_4.data[5*pitch+3], tol);

    MY_CHECK_CLOSE(h_force_4.data[4].x, 0.5*2.949620,tol);
    MY_CHECK_CLOSE(h_force_4.data[4].y, -0.5*2.949620,tol);
    MY_CHECK_SMALL(h_force_4.data[4].z, tol);
    MY_CHECK_CLOSE(h_force_4.data[4].w, 0.5*2.318964, tol);
    MY_CHECK_SMALL(h_virial_4.data[0*pitch+4]
                        +h_virial_4.data[3*pitch+4]
                        +h_virial_4.data[5*pitch+4], tol);

    MY_CHECK_CLOSE(h_force_4.data[5].x, 0.5*3.698439,tol);
    MY_CHECK_CLOSE(h_force_4.data[5].y, -0.5*3.698439,tol);
    MY_CHECK_CLOSE(h_force_4.data[5].z, -0.5*14.245843,tol);
    MY_CHECK_CLOSE(h_force_4.data[5].w, 0.5*2.318964, tol);
    MY_CHECK_SMALL(h_virial_4.data[0*pitch+5]
                        +h_virial_4.data[3*pitch+5]
                        +h_virial_4.data[5*pitch+5], tol);

    MY_CHECK_CLOSE(h_force_4.data[6].x, 0.5*6.648058,tol);
    MY_CHECK_CLOSE(h_force_4.data[6].y, -0.5*6.648058,tol);
    MY_CHECK_CLOSE(h_force_4.data[6].z, -0.5*14.245843,tol);
    MY_CHECK_CLOSE(h_force_4.data[6].w, 0.5*2.318964, tol);
    MY_CHECK_SMALL(h_virial_4.data[0*pitch+6]
                        +h_virial_4.data[3*pitch+6]
                        +h_virial_4.data[5*pitch+6], tol);

    MY_CHECK_CLOSE(h_force_4.data[7].x, -0.5*13.296117,tol);
    MY_CHECK_CLOSE(h_force_4.data[7].y, 0.5*13.296117,tol);
    MY_CHECK_CLOSE(h_force_4.data[7].z, 0.5*28.491686,tol);
    MY_CHECK_CLOSE(h_force_4.data[7].w, 0.5*2.318964, tol);
    MY_CHECK_SMALL(h_virial_4.data[0*pitch+7]
                        +h_virial_4.data[3*pitch+7]
                        +h_virial_4.data[5*pitch+7], tol);
    }

    // one more test: this one will test two things:
    // 1) That the forces are computed correctly even if the particles are rearranged in memory
    // and 2) That two forces can add to the same particle
    std::shared_ptr<SystemDefinition> sysdef_5(new SystemDefinition(5, BoxDim(100.0, 100.0, 100.0), 1, 0, 0, 1, 0, exec_conf));
    std::shared_ptr<ParticleData> pdata_5 = sysdef_5->getParticleData();

    {
    ArrayHandle<Scalar4> h_pos(pdata_5->getPositions(), access_location::host, access_mode::readwrite);
    ArrayHandle<unsigned int> h_tag(pdata_5->getTags(), access_location::host, access_mode::readwrite);
    ArrayHandle<unsigned int> h_rtag(pdata_5->getRTags(), access_location::host, access_mode::readwrite);

    h_pos.data[0].x = Scalar(-9.6); h_pos.data[0].y = -9.0; h_pos.data[0].z = 0.0;
    h_pos.data[1].x =  Scalar(9.6); h_pos.data[1].y = 1.0; h_pos.data[1].z = 0.0;
    h_pos.data[2].x = 0; h_pos.data[2].y = Scalar(-19.6); h_pos.data[2].z = 0.0;
    h_pos.data[3].x = 0; h_pos.data[3].y = Scalar(19.6); h_pos.data[3].z = 10.0;
    h_pos.data[4].x = 0; h_pos.data[4].y = 0; h_pos.data[4].z = Scalar(-29.6);

    h_tag.data[0] = 2;
    h_tag.data[1] = 3;
    h_tag.data[2] = 0;
    h_tag.data[3] = 1;
    h_rtag.data[h_tag.data[0]] = 0;
    h_rtag.data[h_tag.data[1]] = 1;
    h_rtag.data[h_tag.data[2]] = 2;
    h_rtag.data[h_tag.data[3]] = 3;
    }

    // build the dihedral force compute and try it out
    std::shared_ptr<HarmonicDihedralForceCompute> fc_5 = tf_creator(sysdef_5);
    fc_5->setParams(0, 15.0, -1, 4, 0.0);

    sysdef_5->getDihedralData()->addBondedGroup(Dihedral(0, 0,1,2,3));
    sysdef_5->getDihedralData()->addBondedGroup(Dihedral(0, 1,2,3,4));

    fc_5->compute(0);

    {
    GlobalArray<Scalar4>& force_array_5 =  fc_5->getForceArray();
    GlobalArray<Scalar>& virial_array_5 =  fc_5->getVirialArray();
    size_t pitch = virial_array_5.getPitch();
    ArrayHandle<Scalar4> h_force_5(force_array_5,access_location::host,access_mode::read);
    ArrayHandle<Scalar> h_virial_5(virial_array_5,access_location::host,access_mode::read);

    MY_CHECK_CLOSE(h_force_5.data[0].x, -0.5*1.400442, tol);
    MY_CHECK_CLOSE(h_force_5.data[0].y, -0.5*1.251086,tol);
    MY_CHECK_CLOSE(h_force_5.data[0].z, 0.5*3.152951,tol);
    MY_CHECK_CLOSE(h_force_5.data[0].w, 0.5*7.944149, tol);
    MY_CHECK_SMALL(h_virial_5.data[0*pitch+0]
                        +h_virial_5.data[3*pitch+0]
                        +h_virial_5.data[5*pitch+0], tol);

    MY_CHECK_CLOSE(h_force_5.data[1].x, 0.5*1.719594, tol);
    MY_CHECK_CLOSE(h_force_5.data[1].y, -0.5*3.301620,tol);
    MY_CHECK_CLOSE(h_force_5.data[1].z, 0.5*5.293722,tol);
    MY_CHECK_CLOSE(h_force_5.data[1].w, 0.5*7.944149, tol);
    MY_CHECK_SMALL(h_virial_5.data[0*pitch+1]
                        +h_virial_5.data[3*pitch+1]
                        +h_virial_5.data[5*pitch+1], tol);

    MY_CHECK_CLOSE(h_force_5.data[2].x, 0.5*1.153410, tol);
    MY_CHECK_CLOSE(h_force_5.data[2].y, 0.5*1.044598,tol);
    MY_CHECK_CLOSE(h_force_5.data[2].z, -0.5*4.094823,tol);
    MY_CHECK_CLOSE(h_force_5.data[2].w, 0.5*5.176867, tol);
    MY_CHECK_SMALL(h_virial_5.data[0*pitch+2]
                        +h_virial_5.data[3*pitch+2]
                        +h_virial_5.data[5*pitch+2], tol);

    MY_CHECK_CLOSE(h_force_5.data[3].x, -0.5*0.581728, tol);
    MY_CHECK_CLOSE(h_force_5.data[3].y, 0.5*1.797707,tol);
    MY_CHECK_CLOSE(h_force_5.data[3].z, -0.5*4.582985,tol);
    MY_CHECK_CLOSE(h_force_5.data[3].w, 0.5*7.944149, tol);
    MY_CHECK_SMALL(h_virial_5.data[0*pitch+3]
                        +h_virial_5.data[3*pitch+3]
                        +h_virial_5.data[5*pitch+3], tol);

    MY_CHECK_CLOSE(h_force_5.data[4].x, -0.5*0.890834, tol);
    MY_CHECK_CLOSE(h_force_5.data[4].y, 0.5*1.710401,tol);
    MY_CHECK_CLOSE(h_force_5.data[4].z, 0.5*0.231135,tol);
    MY_CHECK_CLOSE(h_force_5.data[4].w, 0.5*2.767281, tol);
    MY_CHECK_SMALL(h_virial_5.data[0*pitch+4]
                        +h_virial_5.data[3*pitch+4]
                        +h_virial_5.data[5*pitch+4], tol);
    }
    }

//! Perform tests for harmonic dihedrals with phase shift
void dihedral_force_phase_shift(dihedralforce_creator tf_creator, std::shared_ptr<ExecutionConfiguration> exec_conf)
    {
    /////////////////////////////////////////////////////////
    // start with the simplest possible test: 4 particles in a huge box with only one dihedral type !!!! NO DIHEDRALS
    std::shared_ptr<SystemDefinition> sysdef_4(new SystemDefinition(4, BoxDim(1000.0), 1, 0, 0, 1, 0, exec_conf));
    std::shared_ptr<ParticleData> pdata_4 = sysdef_4->getParticleData();

    pdata_4->setPosition(0,make_scalar3(0.0,1.0,0.0));
    pdata_4->setPosition(1,make_scalar3(0.0,0.0,0.0));
    pdata_4->setPosition(2,make_scalar3(1.0,0.0,0.0));
    pdata_4->setPosition(3,make_scalar3(0.0,0.0,1.0));

    // create the dihedral force compute to check
    std::shared_ptr<HarmonicDihedralForceCompute> fc_4 = tf_creator(sysdef_4);
    fc_4->setParams(0, Scalar(10.0), 1, 1, Scalar(0.5*M_PI)); // type=0, K=30.0,sign=-1,multiplicity=3, phaseoffset=0, i think the ref angle is 0.240454

    // compute the force and check the results
    fc_4->compute(0);

    {
    GlobalArray<Scalar4>& force_array_1 =  fc_4->getForceArray();
    GlobalArray<Scalar>& virial_array_1 =  fc_4->getVirialArray();

    ArrayHandle<Scalar4> h_force_1(force_array_1,access_location::host,access_mode::read);
    ArrayHandle<Scalar> h_virial_1(virial_array_1,access_location::host,access_mode::read);

    size_t pitch = 0;
    // check that the force is correct, it should be 0 since we haven't created any dihedrals yet
    MY_CHECK_SMALL(h_force_1.data[0].x, tol);
    MY_CHECK_SMALL(h_force_1.data[0].y, tol);
    MY_CHECK_SMALL(h_force_1.data[0].z, tol);
    MY_CHECK_SMALL(h_force_1.data[0].w, tol);
    MY_CHECK_SMALL(h_virial_1.data[0*pitch], tol);
    MY_CHECK_SMALL(h_virial_1.data[1*pitch], tol);
    MY_CHECK_SMALL(h_virial_1.data[2*pitch], tol);
    MY_CHECK_SMALL(h_virial_1.data[3*pitch], tol);
    MY_CHECK_SMALL(h_virial_1.data[4*pitch], tol);
    MY_CHECK_SMALL(h_virial_1.data[5*pitch], tol);
    }


    // add dihedral
    sysdef_4->getDihedralData()->addBondedGroup(Dihedral(0,0,1,2,3)); // add type 0 dihedral between atoms 0-1-2-3
    fc_4->compute(1);

    {
    // this time there should be a force (but they're 0 because eq)
    GlobalArray<Scalar4>& force_array_2 =  fc_4->getForceArray();
    GlobalArray<Scalar>& virial_array_2 =  fc_4->getVirialArray();
    size_t pitch = virial_array_2.getPitch();
    ArrayHandle<Scalar4> h_force_2(force_array_2,access_location::host,access_mode::read);
    ArrayHandle<Scalar> h_virial_2(virial_array_2,access_location::host,access_mode::read);
    /*
    printf(" Particle 1: x = %f  y = %f  z = %f w = %f \n", h_force_2.data[0].x, h_force_2.data[0].y, h_force_2.data[0].z, h_force_2.data[0].w);
    printf(" Particle 2: x = %f  y = %f  z = %f w = %f \n", h_force_2.data[1].x, h_force_2.data[1].y, h_force_2.data[1].z, h_force_2.data[1].w);
    printf(" Particle 3: x = %f  y = %f  z = %f w = %f \n", h_force_2.data[2].x, h_force_2.data[2].y, h_force_2.data[2].z, h_force_2.data[2].w);
    printf(" Particle 4: x = %f  y = %f  z = %f w = %f \n", h_force_2.data[3].x, h_force_2.data[3].y, h_force_2.data[3].z, h_force_2.data[3].w);
    printf( "Virial: %f %f %f %f %f %f \n", h_virial_2.data[0*pitch], h_virial_2.data[1*pitch], h_virial_2.data[2*pitch], h_virial_2.data[3*pitch], h_virial_2.data[4*pitch], h_virial_2.data[5*pitch]);
    printf("\n");
    */


    MY_CHECK_SMALL(h_force_2.data[0].x, tol);
    MY_CHECK_SMALL(h_force_2.data[0].y, tol);
    MY_CHECK_SMALL(h_force_2.data[0].z, tol);
    MY_CHECK_CLOSE(h_force_2.data[0].w, 2.5, tol);
    MY_CHECK_SMALL(h_virial_2.data[0*pitch+0]
                        +h_virial_2.data[3*pitch+0]
                        +h_virial_2.data[5*pitch+0], tol);

    MY_CHECK_SMALL(h_force_2.data[1].x, tol);
    MY_CHECK_SMALL(h_force_2.data[1].y, tol);
    MY_CHECK_SMALL(h_force_2.data[1].z, tol);
    MY_CHECK_CLOSE(h_force_2.data[1].w, 2.5, tol);
    MY_CHECK_SMALL(h_virial_2.data[0*pitch+1]
                        +h_virial_2.data[3*pitch+1]
                        +h_virial_2.data[5*pitch+1], tol);

    MY_CHECK_SMALL(h_force_2.data[2].x, tol);
    MY_CHECK_SMALL(h_force_2.data[2].y, tol);
    MY_CHECK_SMALL(h_force_2.data[2].z, tol);
    MY_CHECK_CLOSE(h_force_2.data[2].w, 2.5, tol);
    MY_CHECK_SMALL(h_virial_2.data[0*pitch+2]
                        +h_virial_2.data[3*pitch+2]
                        +h_virial_2.data[5*pitch+2], tol);

    MY_CHECK_SMALL(h_force_2.data[3].x, tol);
    MY_CHECK_SMALL(h_force_2.data[3].y, tol);
    MY_CHECK_SMALL(h_force_2.data[3].z, tol);
    MY_CHECK_CLOSE(h_force_2.data[3].w, 2.5, tol);
    MY_CHECK_SMALL(h_virial_2.data[0*pitch+3]
                        +h_virial_2.data[3*pitch+3]
                        +h_virial_2.data[5*pitch+3], tol);
    }


    }



//! Compares the output of two HarmonicDihedralForceComputes
void dihedral_force_comparison_tests(dihedralforce_creator tf_creator1,
                                     dihedralforce_creator tf_creator2,
                                     std::shared_ptr<ExecutionConfiguration> exec_conf)
    {
    const unsigned int N = 1000;

    // create a particle system to sum forces on
    // just randomly place particles. We don't really care how huge the bond forces get: this is just a unit test
    RandomInitializer rand_init(N, Scalar(0.2), Scalar(0.9), "A");
    std::shared_ptr< SnapshotSystemData<Scalar> > snap = rand_init.getSnapshot();
    snap->dihedral_data.type_mapping.push_back("A");
    std::shared_ptr<SystemDefinition> sysdef(new SystemDefinition(snap, exec_conf));

    std::shared_ptr<HarmonicDihedralForceCompute> fc1 = tf_creator1(sysdef);
    std::shared_ptr<HarmonicDihedralForceCompute> fc2 = tf_creator2(sysdef);
    fc1->setParams(0, Scalar(3.0), -1, 3, Scalar(0.0));
    fc2->setParams(0, Scalar(3.0), -1, 3, Scalar(0.0));

    // add dihedrals
    for (unsigned int i = 0; i < N-3; i++)
        {
        sysdef->getDihedralData()->addBondedGroup(Dihedral(0, i, i+1,i+2, i+3));
        }

    // compute the forces
    fc1->compute(0);
    fc2->compute(0);

    // verify that the forces are identical (within roundoff errors)
    {
    GlobalArray<Scalar4>& force_array_7 =  fc1->getForceArray();
    GlobalArray<Scalar>& virial_array_7 =  fc1->getVirialArray();
    size_t pitch = virial_array_7.getPitch();
    ArrayHandle<Scalar4> h_force_7(force_array_7,access_location::host,access_mode::read);
    ArrayHandle<Scalar> h_virial_7(virial_array_7,access_location::host,access_mode::read);
    GlobalArray<Scalar4>& force_array_8 =  fc2->getForceArray();
    GlobalArray<Scalar>& virial_array_8 =  fc2->getVirialArray();
    ArrayHandle<Scalar4> h_force_8(force_array_8,access_location::host,access_mode::read);
    ArrayHandle<Scalar> h_virial_8(virial_array_8,access_location::host,access_mode::read);

    // compare average deviation between the two computes
    double deltaf2 = 0.0;
    double deltape2 = 0.0;
    double deltav2[6];
    for (unsigned int i = 0; i < 6; i++)
        deltav2[i] = 0.0;

    for (unsigned int i = 0; i < N; i++)
        {
        deltaf2 += double(h_force_8.data[i].x - h_force_7.data[i].x) * double(h_force_8.data[i].x - h_force_7.data[i].x);
        deltaf2 += double(h_force_8.data[i].y - h_force_7.data[i].y) * double(h_force_8.data[i].y - h_force_7.data[i].y);
        deltaf2 += double(h_force_8.data[i].z - h_force_7.data[i].z) * double(h_force_8.data[i].z - h_force_7.data[i].z);
        deltape2 += double(h_force_8.data[i].w - h_force_7.data[i].w) * double(h_force_8.data[i].w - h_force_7.data[i].w);
        for (unsigned int j = 0; j < 6; j++)
            deltav2[j] += double(h_virial_8.data[j*pitch+i] - h_virial_7.data[j*pitch+i]) * double(h_virial_8.data[j*pitch+i] - h_virial_7.data[j*pitch+i]);

        // also check that each individual calculation is somewhat close
        }
    deltaf2 /= double(N);
    deltape2 /= double(N);
    for (unsigned int j = 0; j < 6; j++)
        deltav2[j] /= double(N);

    CHECK_SMALL(deltaf2, double(tol_small));
    CHECK_SMALL(deltape2, double(tol_small));
    CHECK_SMALL(deltav2[0], double(tol_small));
    CHECK_SMALL(deltav2[1], double(tol_small));
    CHECK_SMALL(deltav2[2], double(tol_small));
    CHECK_SMALL(deltav2[3], double(tol_small));
    CHECK_SMALL(deltav2[4], double(tol_small));
    CHECK_SMALL(deltav2[5], double(tol_small));
    }
    }


//! HarmonicDihedralForceCompute creator for dihedral_force_basic_tests()
std::shared_ptr<HarmonicDihedralForceCompute> base_class_tf_creator(std::shared_ptr<SystemDefinition> sysdef)
    {
    return std::shared_ptr<HarmonicDihedralForceCompute>(new HarmonicDihedralForceCompute(sysdef));
    }

#ifdef ENABLE_HIP
//! DihedralForceCompute creator for bond_force_basic_tests()
std::shared_ptr<HarmonicDihedralForceCompute> gpu_tf_creator(std::shared_ptr<SystemDefinition> sysdef)
    {
    return std::shared_ptr<HarmonicDihedralForceCompute>(new HarmonicDihedralForceComputeGPU(sysdef));
    }
#endif

//! test case for dihedral forces on the CPU
UP_TEST( HarmonicDihedralForceCompute_basic )
    {
    printf(" IN UP_TEST: CPU \n");
    dihedralforce_creator tf_creator = bind(base_class_tf_creator, _1);
    dihedral_force_basic_tests(tf_creator, std::shared_ptr<ExecutionConfiguration>(new ExecutionConfiguration(ExecutionConfiguration::CPU)));
    dihedral_force_phase_shift(tf_creator, std::shared_ptr<ExecutionConfiguration>(new ExecutionConfiguration(ExecutionConfiguration::CPU)));
    }

#ifdef ENABLE_HIP
//! test case for dihedral forces on the GPU
UP_TEST( HarmonicDihedralForceComputeGPU_basic )
    {
    printf(" IN UP_TEST: GPU \n");
    dihedralforce_creator tf_creator = bind(gpu_tf_creator, _1);
    dihedral_force_basic_tests(tf_creator, std::shared_ptr<ExecutionConfiguration>(new ExecutionConfiguration(ExecutionConfiguration::GPU)));
    dihedral_force_phase_shift(tf_creator, std::shared_ptr<ExecutionConfiguration>(new ExecutionConfiguration(ExecutionConfiguration::GPU)));
    }

//! test case for comparing bond GPU and CPU BondForceComputes
UP_TEST( HarmonicDihedralForceComputeGPU_compare )
    {
    dihedralforce_creator tf_creator_gpu = bind(gpu_tf_creator, _1);
    dihedralforce_creator tf_creator = bind(base_class_tf_creator, _1);
    dihedral_force_comparison_tests(tf_creator, tf_creator_gpu, std::shared_ptr<ExecutionConfiguration>(new ExecutionConfiguration(ExecutionConfiguration::GPU)));
    }

//! test case for comparing calculation on the CPU to multi-gpu ones
UP_TEST( HarmonicDihedralForce_MultiGPU_compare)
    {
    std::shared_ptr<ExecutionConfiguration> exec_conf(new ExecutionConfiguration(ExecutionConfiguration::GPU));

    dihedralforce_creator tf_creator_gpu = bind(gpu_tf_creator, _1);
    dihedralforce_creator tf_creator = bind(base_class_tf_creator, _1);
    dihedral_force_comparison_tests(tf_creator, tf_creator_gpu, exec_conf);
    }
#endif
