LinearPerturbation.h

#ifndef MCMD_LINEAR_PERTURBATION_H
#define MCMD_LINEAR_PERTURBATION_H

/*
* Simpatico - Simulation Package for Polymeric and Molecular Liquids
*
* Copyright 2010 - 2017, The Regents of the University of Minnesota
* Distributed under the terms of the GNU General Public License.
*/

#include "Perturbation.h"

namespace McMd
{

   template <class SystemType>
   class LinearPerturbation : public Perturbation
   {
   
   public:

      using Perturbation::getNParameters;
      using Perturbation::parameter;
      using Perturbation::derivative;

      LinearPerturbation(SystemType& system, int size, int rank);

      virtual ~LinearPerturbation();

      virtual double difference(DArray<double> iPartnerParameter) const;

      SystemType& system() const;

   private:

      SystemType* systemPtr_;

   };

   // Methods

   /*
   * Constructor. 
   */
   template <class SystemType>
   LinearPerturbation<SystemType>
        ::LinearPerturbation(SystemType& system, int size, int rank)
    : Perturbation(size, rank),
      systemPtr_(&system)
   {}

   template <class SystemType>
   LinearPerturbation<SystemType>::~LinearPerturbation()
   {}

   /*
   * Returns the difference W(partner) - W(current).
   */
   template <class SystemType>
   double LinearPerturbation<SystemType>::difference(DArray<double> iPartnerParameter) const
   {  
      int nParameters = getNParameters();
      double difference = 0.0;
      for (int i = 0; i < nParameters; ++i) {
         difference += (iPartnerParameter[i] - parameter(i)) * derivative(i); 
      }
      return difference;
   }

   /*
   * Return associated System by reference.
   */
   template <class SystemType>
   inline SystemType& LinearPerturbation<SystemType>::system() const
   {  return *systemPtr_; }

}
      
#endif  // ifndef LINEAR_PERTURBATION_H