Line data    Source code

       1             : /* +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
       2             :    Copyright (c) 2011-2023 The plumed team
       3             :    (see the PEOPLE file at the root of the distribution for a list of names)
       4             : 
       5             :    See http://www.plumed.org for more information.
       6             : 
       7             :    This file is part of plumed, version 2.
       8             : 
       9             :    plumed is free software: you can redistribute it and/or modify
      10             :    it under the terms of the GNU Lesser General Public License as published by
      11             :    the Free Software Foundation, either version 3 of the License, or
      12             :    (at your option) any later version.
      13             : 
      14             :    plumed is distributed in the hope that it will be useful,
      15             :    but WITHOUT ANY WARRANTY; without even the implied warranty of
      16             :    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      17             :    GNU Lesser General Public License for more details.
      18             : 
      19             :    You should have received a copy of the GNU Lesser General Public License
      20             :    along with plumed.  If not, see <http://www.gnu.org/licenses/>.
      21             : +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ */
      22             : #ifndef __PLUMED_tools_Angle_h
      23             : #define __PLUMED_tools_Angle_h
      24             : 
      25             : #include "Vector.h"
      26             : #include "Tools.h"
      27             : #include <cmath>
      28             : #include <limits>
      29             : 
      30             : namespace PLMD {
      31             : 
      32             : /// \ingroup TOOLBOX
      33             : /// Class to compute angles.
      34             : /// I define it as a class even if it does not contain anything. The reason
      35             : /// is that in the future I would like to extend it to contain options about
      36             : /// how the calculation should be done. So, for now use it as
      37             : /// Angle a;
      38             : /// double angle=a.compute(v1,v2);
      39             : /// I know it is a bit misleading. If we really do not need to store "options"
      40             : /// inside the Angle class, we can remove it later and write compute as
      41             : /// a static function.
      42             : class Angle {
      43             : // still empty, but may accommodate some options in the future
      44             : public:
      45             : /// Compute the angle between vectors v1 and v2
      46             :   template <typename T>
      47             :   static T compute(const VectorTyped<T,3> v1,const VectorTyped<T,3> v2) {
      48             :     return std::acos(dotProduct(v1,v2)/(v1.modulo()*v2.modulo()));
      49             :   }
      50             : /// Compute the angle between vectors v1 and v2 and its derivatives wrt v1 and v2
      51             :   template <typename T>
      52      784680 :   static T compute(const VectorTyped<T,3> v1,
      53             :                    const VectorTyped<T,3> v2,
      54             :                    VectorTyped<T,3>& d1,
      55             :                    VectorTyped<T,3>& d2) {
      56             :     using V3=VectorTyped<T,3>;
      57             :     const T dp(dotProduct(v1,v2));
      58             :     const V3& dp_dv1(v2);
      59             :     const V3& dp_dv2(v1);
      60             :     const T sv1(v1.modulo2());
      61             :     const T sv2(v2.modulo2());
      62             :     const V3 dsv1_dv1(2*v1);
      63             :     const V3 dsv2_dv2(2*v2);
      64      784680 :     const T nn(1.0/std::sqrt(sv1*sv2));
      65      784680 :     const V3 dnn_dv1(-0.5*nn/sv1*dsv1_dv1);
      66      784680 :     const V3 dnn_dv2(-0.5*nn/sv2*dsv2_dv2);
      67             : 
      68      784680 :     const T dpnn(dp*nn);
      69             :     // the tolerance must be T's: PLMD::epsilon is double's, which for float means "exactly 1"
      70             :     const T eps(std::numeric_limits<T>::epsilon());
      71      784680 :     if(dpnn>=1.0-eps) {
      72           0 :       d1=V3(0.0,0.0,0.0);
      73           0 :       d2=V3(0.0,0.0,0.0);
      74           0 :       return 0.0;
      75             :     }
      76      784680 :     if(dpnn<=-1.0+eps) {
      77           0 :       d1=V3(0.0,0.0,0.0);
      78           0 :       d2=V3(0.0,0.0,0.0);
      79           0 :       return pi;
      80             :     }
      81             :     const V3 ddpnn_dv1(dp*dnn_dv1+dp_dv1*nn);
      82             :     const V3 ddpnn_dv2(dp*dnn_dv2+dp_dv2*nn);
      83             : 
      84      784680 :     const T x(-1.0/std::sqrt(1-dpnn*dpnn));
      85             : 
      86      784680 :     d1=x*ddpnn_dv1;
      87      784680 :     d2=x*ddpnn_dv2;
      88             : 
      89             : 
      90      784680 :     return std::acos(dpnn);
      91             :   }
      92             : 
      93             : };
      94             : 
      95             : }
      96             : 
      97             : #endif