Dogcows Code - chaz/yoink/blob - src/Moof/RK4.hh

   1
   2 /*******************************************************************************
   3
   4  Copyright (c) 2009, Charles McGarvey
   5  All rights reserved.
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  11      this list of conditions and the following disclaimer.
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  13      this  list of conditions and the following disclaimer in the documentation
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  27 *******************************************************************************/
  28
  29 #ifndef _MOOF_RK4_HH_
  30 #define _MOOF_RK4_HH_
  31
  32 #include <Moof/Math.hh>
  33
  34
  35 namespace Mf {
  36
  37 // Generic implementations of a few simple integrators.  To use, you need one
  38 // type representing the state and another containing the derivatives of the
  39 // primary state variables.  The state class must implement these methods:
  40 //
  41 // void getDerivative(Derivative_Type& derivative, Scalar absoluteTime);
  42 // void applyDerivative(const Derivative_Type& derivative, Scalar deltaTime);
  43 //
  44 // Additionally, the derivative class must overload a few operators:
  45 //
  46 // Derivative_Type operator+(const Derivative_Type& other) const
  47 // Derivative_Type operator*(const Derivative_Type& other) const
  48
  49 template<typename S, typename D>
  50 inline D evaluate(const S& state, Scalar t)
  51 {
  52         D derivative;
  53         state.getDerivative(derivative, t);
  54         return derivative;
  55 }
  56
  57 template<typename S, typename D>
  58 inline D evaluate(const S& state,  Scalar t, Scalar dt, const D& derivative)
  59 {
  60         S temp = state;
  61         temp.applyDerivative(derivative, dt);
  62         return evaluate<S,D>(temp, t + dt);
  63 }
  64
  65
  66 template<typename S, typename D>
  67 inline void euler(S& state, Scalar t, Scalar dt)
  68 {
  69         D a = evaluate<S,D>(state, t);
  70
  71         state.applyDerivative(a, dt);
  72 }
  73
  74 template<typename S, typename D>
  75 inline void rk2(S& state, Scalar t, Scalar dt)
  76 {
  77         D a = evaluate<S,D>(state, t);
  78         D b = evaluate<S,D>(state, t, dt * 0.5, a);
  79
  80         state.applyDerivative(b, dt);
  81 }
  82
  83 template<typename S, typename D>
  84 inline void rk4(S& state, Scalar t, Scalar dt)
  85 {
  86         D a = evaluate<S,D>(state, t);
  87         D b = evaluate<S,D>(state, t, dt * 0.5, a);
  88         D c = evaluate<S,D>(state, t, dt * 0.5, b);
  89         D d = evaluate<S,D>(state, t, dt, c);
  90
  91         state.applyDerivative((a + (b + c) * 2.0 + d) * (1.0/6.0), dt);
  92 }
  93
  94
  95 } // namespace Mf
  96
  97 #endif // _MOOF_RK4_HH_
  98
  99 /** vim: set ts=4 sw=4 tw=80: *************************************************/
 100