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 * Contributors: Pande Group
 *
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 * a copy of this software and associated documentation files (the
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 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject
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 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
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 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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#ifndef __ReferenceLangevinMiddleDynamics_H__
#define __ReferenceLangevinMiddleDynamics_H__

#include "ReferenceDynamics.h"
#include "openmm/internal/ContextImpl.h"
#include "openmm/internal/windowsExport.h"

namespace OpenMM {

class OPENMM_EXPORT ReferenceLangevinMiddleDynamics : public ReferenceDynamics {

   protected:

      std::vector<OpenMM::Vec3> xPrime, oldx;
      std::vector<double> inverseMasses;
      double friction;
      
   public:

      /**---------------------------------------------------------------------------------------
      
         Constructor

         @param numberOfAtoms  number of atoms
         @param deltaT         delta t for dynamics
         @param friction       friction coefficient
         @param temperature    temperature
      
         --------------------------------------------------------------------------------------- */

       ReferenceLangevinMiddleDynamics(int numberOfAtoms, double deltaT, double friction, double temperature);

      /**---------------------------------------------------------------------------------------
      
         Destructor
      
         --------------------------------------------------------------------------------------- */

       ~ReferenceLangevinMiddleDynamics();

      /**---------------------------------------------------------------------------------------
      
         Get friction coefficient
      
         --------------------------------------------------------------------------------------- */
      
      double getFriction() const;
      
      /**---------------------------------------------------------------------------------------
      
         Update
      
         @param context             the context this integrator is updating
         @param system              the System to be integrated
         @param atomCoordinates     atom coordinates
         @param velocities          velocities
         @param masses              atom masses
         @param tolerance           the constraint tolerance
      
         --------------------------------------------------------------------------------------- */
     
      void update(OpenMM::ContextImpl& context, std::vector<OpenMM::Vec3>& atomCoordinates,
                  std::vector<OpenMM::Vec3>& velocities, std::vector<double>& masses, double tolerance);
     
      /**---------------------------------------------------------------------------------------
            
         @param numberOfAtoms       number of atoms
         @param velocities          velocities
         @param forces              forces
         @param inverseMasses       inverse atom masses
      
         --------------------------------------------------------------------------------------- */
      
      virtual void updatePart1(int numberOfAtoms, std::vector<OpenMM::Vec3>& velocities,  std::vector<OpenMM::Vec3>& forces, std::vector<double>& inverseMasses);
      
      /**---------------------------------------------------------------------------------------
      
         Second update
      
         @param numberOfAtoms       number of atoms
         @param atomCoordinates     atom coordinates
         @param velocities          velocities
         @param inverseMasses       inverse atom masses
         @param xPrime              xPrime
      
         --------------------------------------------------------------------------------------- */
      
      virtual void updatePart2(int numberOfAtoms, std::vector<OpenMM::Vec3>& atomCoordinates, std::vector<OpenMM::Vec3>& velocities,
                               std::vector<double>& inverseMasses, std::vector<OpenMM::Vec3>& xPrime);
      
      /**---------------------------------------------------------------------------------------
      
         Third update
      
         @param context             the context this integrator is updating
         @param numberOfAtoms       number of atoms
         @param atomCoordinates     atom coordinates
         @param velocities          velocities
         @param inverseMasses       inverse atom masses
         @param xPrime              xPrime
      
         --------------------------------------------------------------------------------------- */
      
      virtual void updatePart3(OpenMM::ContextImpl& context, int numberOfAtoms, std::vector<OpenMM::Vec3>& atomCoordinates, std::vector<OpenMM::Vec3>& velocities,
                               std::vector<double>& inverseMasses, std::vector<OpenMM::Vec3>& xPrime);
};

} // namespace OpenMM

#endif // __ReferenceLangevinMiddleDynamics_H__
