BendForce.h

#ifndef SIMP_BEND_FORCE_H
#define SIMP_BEND_FORCE_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 "Bend.h"   // base class

#include <cmath>

namespace Simp
{

   using namespace Util;

   struct BendForce : public Bend
   {
   
   public:

      Vector d1;

      Vector d2;
   
      void computeDerivatives(const Vector& b1, const Vector& b2);

   };

   // Inline method definitions
   
   /* 
   * Calculate cosTheta and unit vectors.
   */
   inline
   void BendForce::computeDerivatives(const Vector& b1, const Vector& b2)
   {
      Vector u1, u2;

      double b1Abs = b1.abs();
      u1.divide(b1, b1Abs);

      double b2Abs = b2.abs();
      u2.divide(b2, b2Abs);

      cosTheta = u1.dot(u2);

      Vector t;
      t.multiply(u1, cosTheta);
      d1.subtract(u2, t);
      d1 /= b1Abs;

      t.multiply(u2, cosTheta);
      d2.subtract(u1, t);
      d2 /= b2Abs;
   }

} 
#endif