806127ecc977c1388b2dcef37f838f2658f86f77
[chaz/yoink] / src / Moof / RK4.hh
1
2 /*******************************************************************************
3
4 Copyright (c) 2009, Charles McGarvey
5 All rights reserved.
6
7 Redistribution and use in source and binary forms, with or without
8 modification, are permitted provided that the following conditions are met:
9
10 * Redistributions of source code must retain the above copyright notice,
11 this list of conditions and the following disclaimer.
12 * Redistributions in binary form must reproduce the above copyright notice,
13 this list of conditions and the following disclaimer in the documentation
14 and/or other materials provided with the distribution.
15
16 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
17 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
19 DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
20 FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
22 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
23 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
25 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26
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
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