TestBrookVerletIntegrator.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) 2009 Stanford University and the Authors.           *
 * Authors: Peter Eastman, Mark Friedrichs                                    *
 * Contributors:                                                              *
 *                                                                            *
 * This program is free software: you can redistribute it and/or modify       *
 * it under the terms of the GNU Lesser General Public License as published   *
 * by the Free Software Foundation, either version 3 of the License, or       *
 * (at your option) any later version.                                        *
 *                                                                            *
 * This program is distributed in the hope that it will be useful,            *
 * but WITHOUT ANY WARRANTY; without even the implied warranty of             *
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the              *
 * GNU Lesser General Public License for more details.                        *
 *                                                                            *
 * You should have received a copy of the GNU Lesser General Public License   *
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.      *
 * -------------------------------------------------------------------------- */

/**
 * This tests the Brook harmonic angle bond force/energy
 */

#include <vector>

#include "../../../tests/AssertionUtilities.h"
#include "BrookPlatform.h"
#include "ReferencePlatform.h"
#include "openmm/OpenMMContext.h"
#include "openmm/HarmonicBondForce.h"
#include "openmm/NonbondedForce.h"
#include "openmm/CMMotionRemover.h"
#include "openmm/System.h"
#include "openmm/VerletIntegrator.h"
#include "../src/sfmt/SFMT.h"

#define PI_M               3.141592653589

using namespace OpenMM;
using namespace std;

const double TOL = 1e-5;

void testVerletSingleBond( FILE* log ){

// ---------------------------------------------------------------------------------------

   static const std::string methodName      = "testVerletSingleBond";
   int PrintOn                              = 1; 
   
   int numberOfParticles                    = 2;
   double mass                              = 2.0; 

// ---------------------------------------------------------------------------------------

   PrintOn = log ? PrintOn : 0;

   if( PrintOn ){
      (void) fprintf( log, "%s\n", methodName.c_str() ); (void) fflush( log );
   }   

   BrookPlatform platform( 32, "cal", log );

   System system; 
   system.addParticle(2.0);
   system.addParticle(2.0);

   VerletIntegrator integrator(0.001);

   HarmonicBondForce* forceField = new HarmonicBondForce();
   forceField->addBond(0, 1, 1.5, 1);
   system.addForce(forceField);

//   CMMotionRemover* remover = new CMMotionRemover();
//   system.addForce(remover);

   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();
   if( PrintOn ){
      (void) fprintf( log, "%s Energy initialEnergy=%12.5e KE=%12.5e PE=%12.5e\n",
                      methodName.c_str(), initialEnergy,
                      state.getKineticEnergy(), state.getPotentialEnergy() );
       (void) fflush( log );
   }


   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);

       Vec3 position0 = state.getPositions()[0];
       Vec3 position1 = state.getPositions()[1];
       if( PrintOn > 1 ){
          (void) fprintf( log, "%s %d Pos expected=[%12.5e 0 0] actual=[%12.5e %12.5e %12.5e] [%12.5e %12.5e %12.5e]\n",
                          methodName.c_str(), i, -0.5*expectedDist, 
                          position0[0], position0[1], position0[2],
                          position1[0], position1[1], position1[2] );
          (void) fflush( log );
       }

       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);

       Vec3 velocity0 = state.getVelocities()[0];
       Vec3 velocity1 = state.getVelocities()[1];
       if( PrintOn > 1 ){
          (void) fprintf( log, "%s %d Vel expected=[%12.5e 0 0] actual=[%12.5e %12.5e %12.5e] [%12.5e %12.5e %12.5e]\n",
                          methodName.c_str(), i, -0.5*expectedSpeed, 
                          velocity0[0], velocity0[1], velocity0[2],
                          velocity1[0], velocity1[1], velocity1[2] );
          (void) fflush( log );
       }

       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();

       if( PrintOn > 1 ){
          (void) fprintf( log, "%s %d Energy initialEnergy=%12.5e actual=%12.5e KE=%12.5e PE=%12.5e\n",
                          methodName.c_str(), i, initialEnergy, energy,
                          state.getKineticEnergy(), state.getPotentialEnergy() );
          (void) fflush( log );
       }

       ASSERT_EQUAL_TOL(initialEnergy, energy, 0.01);
       integrator.step(1);
   }   

   if( PrintOn ){
      (void) fprintf( log, "%s ok\n", methodName.c_str() );
      (void) fflush( log );
   }

}

void testVerletConstraints( FILE* log ){

// ---------------------------------------------------------------------------------------

  static const std::string methodName      = "testVerletConstraints";
  int PrintOn                              = 1; 
  
  const int numParticles                   = 8;
  const int numConstraints                 = numParticles/2;
  double mass                              = 10.0; 

// ---------------------------------------------------------------------------------------

   PrintOn = log ? PrintOn : 0;

   if( PrintOn ){
      (void) fprintf( log, "%s\n", methodName.c_str() ); (void) fflush( log );
   }   

   //ReferencePlatform platform;
   BrookPlatform platform( 32, "cal", log );
   System system;
   VerletIntegrator integrator(0.001);
   integrator.setConstraintTolerance(1e-5);
   NonbondedForce* forceField = new NonbondedForce();
   for (int i = 0; i < numParticles; ++i) {
       system.addParticle(mass);
       forceField->addParticle((i%2 == 0 ? 0.2 : -0.2), 0.5, 5.0);
   }
   for (int i = 0; i < numConstraints; ++i){
       system.addConstraint(2*i, 2*i+1, 1.0);
   }
   system.addForce(forceField);

   //CMMotionRemover* remover = new CMMotionRemover();
   //system.addForce(remover);

   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;
   double tolerance     = 0.002;
   double maxDiff       = -1.0;
   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]));
         double diff =  fabs( distance - dist );
         if( diff > maxDiff ){
            maxDiff = diff;
         }
         if( PrintOn > 1 || diff > tolerance ){
            (void) fprintf( log, "%s step=%d cnstrnt=%d p[%d %d] d=%.5e exptd=%.5e dif=%.5e [%.5e %.5e %.5e] [%.5e %.5e %.5e] mxDff=%.5e\n", 
                            methodName.c_str(), i, j, particle1, particle2, dist, distance, diff,
                            p1[0], p1[1], p1[2], p2[0], p2[1], p2[2], maxDiff); (void) fflush( log );
         }
         ASSERT_EQUAL_TOL(distance, dist, tolerance );
       }

       double energy = state.getKineticEnergy()+state.getPotentialEnergy();
       if( PrintOn > 1 ){
          (void) fprintf( log, "%s %d e[%.5e %.5e] ke=%.5e pe=%.5e\n", 
                          methodName.c_str(), i, initialEnergy, energy, state.getKineticEnergy(), state.getPotentialEnergy() ); (void) fflush( log );
       }
       if( i == 1 ){
           initialEnergy = energy;
       } else if( i > 1 ){
           ASSERT_EQUAL_TOL(initialEnergy, energy, 0.5);
       }
       integrator.step(1);
   }
   if( PrintOn ){
      (void) fprintf( log, "%s ok maxShakeDiff=%.5e tolerance=%.5e\n", methodName.c_str(), maxDiff, tolerance );
      (void) fflush( log );
   }
}

int main( ){

// ---------------------------------------------------------------------------------------

   static const std::string methodName      = "testBrookVerletIntegrator";
   FILE* log                                = stdout;

// ---------------------------------------------------------------------------------------

   (void) fflush( stdout );
   (void) fflush( stderr );
   try {
      testVerletSingleBond( log );
      testVerletConstraints( log );
    } catch( const exception& e ){
      (void) fprintf( log, "Exception %s %.s\n", methodName.c_str(),  e.what() ); (void) fflush( log );
      return 1;
   }   
   (void) fprintf( log, "\n%s done\n", methodName.c_str() ); (void) fflush( log );

   return 0;
}