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#ifndef OPENTISSUE_CORE_GEOMETRY_GEOMETRY_COT_H
#define OPENTISSUE_CORE_GEOMETRY_GEOMETRY_COT_H
//
// OpenTissue Template Library
// - A generic toolbox for physics-based modeling and simulation.
// Copyright (C) 2008 Department of Computer Science, University of Copenhagen.
//
// OTTL is licensed under zlib: http://opensource.org/licenses/zlib-license.php
//
#include <OpenTissue/configuration.h>

#include <cmath>   // Needed for std::sqrt and std::fabs

namespace OpenTissue
{
  namespace geometry
  {

    template<typename vector_type>
    typename vector_type::value_type cot(vector_type const & p, vector_type const & pi, vector_type const & pj)  
    {
      using std::sqrt;
      using std::fabs;

      typedef typename vector_type::value_type   real_type;

      static const real_type zero = real_type(); // By standard default constructed integral types are zero

      vector_type u = pi-p;
      vector_type v = pj-p;
      real_type dot = u*v;
      real_type denom = sqrt( (u*u)*(v*v) - dot*dot );

      return (fabs(denom)>zero)? (dot/denom) : zero; 
    }

  } // namespace geometry
} // namespace OpenTissue

//OPENTISSUE_CORE_GEOMETRY_GEOMETRY_COT_H
#endif