libhoomd/computes/EvaluatorConstraintSphere.h

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   2 Highly Optimized Object-oriented Many-particle Dynamics -- Blue Edition
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  49
  50 // Maintainer: joaander
  51
  52 #ifndef __EVALUATOR_CONSTRAINT_SPHERE_H__
  53 #define __EVALUATOR_CONSTRAINT_SPHERE_H__
  54
  55 #include "HOOMDMath.h"
  56
  57 /*! \file EvaluatorConstraintSphere.h
  58     \brief Defines the constraint evaluator class for spheres
  59 */
  60
  61 // need to declare these class methods with __device__ qualifiers when building in nvcc
  62 // DEVICE is __host__ __device__ when included in nvcc and blank when included into the host compiler
  63 #ifdef NVCC
  64 #define DEVICE __device__
  65 #else
  66 #define DEVICE
  67 #endif
  68
  69 //! Class for evaluating sphere constraints
  70 /*! <b>General Overview</b>
  71     EvaluatorConstraintSphere is a low level computation helper class to aid in evaluating particle constraints on a
  72     sphere. Given a sphere at a given position and radius, it will find the nearest point on the sphere to a given
  73     point.
  74 */
  75 class EvaluatorConstraintSphere
  76     {
  77     public:
  78         //! Constructs the constraint evaluator
  79         /*! \param _P Position of the sphere
  80             \param _r   Radius of the sphere
  81         */
  82         DEVICE EvaluatorConstraintSphere(Scalar3 _P, Scalar _r)
  83             : P(_P), r(_r)
  84             {
  85             }
  86
  87         //! Evaluate the closest point on the sphere
  88         /*! \param U unconstrained point
  89
  90             \return Nearest point on the sphere
  91         */
  92         DEVICE Scalar3 evalClosest(const Scalar3& U)
  93             {
  94             // compute the vector pointing from P to V
  95             Scalar3 V;
  96             V.x = U.x - P.x;
  97             V.y = U.y - P.y;
  98             V.z = U.z - P.z;
  99
 100             // compute 1/magnitude of V
 101             Scalar magVinv = fast::rsqrt(V.x*V.x + V.y*V.y + V.z*V.z);
 102
 103             // compute Vhat, the unit vector pointing in the direction of V
 104             Scalar3 Vhat;
 105             Vhat.x = magVinv * V.x;
 106             Vhat.y = magVinv * V.y;
 107             Vhat.z = magVinv * V.z;
 108
 109             // compute resulting constrained point
 110             Scalar3 C;
 111 #if(NVCC && __CUDA_ARCH__ < 200)
 112             C.x = P.x + __fmul_rn(Vhat.x,r);
 113             C.y = P.y + __fmul_rn(Vhat.y,r);
 114             C.z = P.z + __fmul_rn(Vhat.z,r);
 115 #else
 116             C.x = P.x + Vhat.x * r;
 117             C.y = P.y + Vhat.y * r;
 118             C.z = P.z + Vhat.z * r;
 119 #endif
 120
 121             return C;
 122             }
 123
 124     protected:
 125         Scalar3 P;      //!< Position of the sphere
 126         Scalar r;       //!< radius of the sphere
 127     };
 128
 129
 130 #endif // __PAIR_EVALUATOR_LJ_H__