Bend.h

#ifndef SIMP_BEND_H
#define SIMP_BEND_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 <util/space/Vector.h>

#include <cmath>

namespace Simp
{

   using namespace Util;

   struct Bend
   {
   
   public:

      double cosTheta;

      void computeAngle(const Vector& b1, const Vector& b2);
 
      double sinTheta() const;

      double theta() const;

   };

   // Inline method definitions
   
   /* 
   * Calculate unit bond vectors and cosTheta.
   */
   inline
   void Bend::computeAngle(const Vector& b1, const Vector& b2) 
   {
      double d = sqrt(b1.square()*b2.square());
      cosTheta = b1.dot(b2)/d;
      if (cosTheta >  1.0) cosTheta =  1.0;
      if (cosTheta < -1.0) cosTheta = -1.0;
   }

   /*
   * Return value sin(theta) for precomputed cos(theta).
   */
   inline
   double Bend::sinTheta() const
   {  return sqrt(1.0 - cosTheta*cosTheta); }

   /*
   * Return theta in radians for precomputed cos(theta).
   */
   inline
   double Bend::theta() const
   {  return std::acos(cosTheta); }

} 
#endif