Blender  V3.3
btConjugateGradient.h
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1 /*
2  Written by Xuchen Han <xuchenhan2015@u.northwestern.edu>
3 
4  Bullet Continuous Collision Detection and Physics Library
5  Copyright (c) 2019 Google Inc. http://bulletphysics.org
6  This software is provided 'as-is', without any express or implied warranty.
7  In no event will the authors be held liable for any damages arising from the use of this software.
8  Permission is granted to anyone to use this software for any purpose,
9  including commercial applications, and to alter it and redistribute it freely,
10  subject to the following restrictions:
11  1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
12  2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
13  3. This notice may not be removed or altered from any source distribution.
14  */
15 
16 #ifndef BT_CONJUGATE_GRADIENT_H
17 #define BT_CONJUGATE_GRADIENT_H
18 #include "btKrylovSolver.h"
19 template <class MatrixX>
20 class btConjugateGradient : public btKrylovSolver<MatrixX>
21 {
24  TVStack r, p, z, temp;
25 
26 public:
27  btConjugateGradient(const int max_it_in)
28  : btKrylovSolver<MatrixX>(max_it_in, SIMD_EPSILON)
29  {
30  }
31 
32  virtual ~btConjugateGradient() {}
33 
34  // return the number of iterations taken
35  int solve(MatrixX& A, TVStack& x, const TVStack& b, bool verbose = false)
36  {
37  BT_PROFILE("CGSolve");
38  btAssert(x.size() == b.size());
39  reinitialize(b);
40  temp = b;
41  A.project(temp);
42  p = temp;
43  A.precondition(p, z);
44  btScalar d0 = this->dot(z, temp);
45  d0 = btMin(btScalar(1), d0);
46  // r = b - A * x --with assigned dof zeroed out
47  A.multiply(x, temp);
48  r = this->sub(b, temp);
49  A.project(r);
50  // z = M^(-1) * r
51  A.precondition(r, z);
52  A.project(z);
53  btScalar r_dot_z = this->dot(z, r);
54  if (r_dot_z <= Base::m_tolerance * d0)
55  {
56  if (verbose)
57  {
58  std::cout << "Iteration = 0" << std::endl;
59  std::cout << "Two norm of the residual = " << r_dot_z << std::endl;
60  }
61  return 0;
62  }
63  p = z;
64  btScalar r_dot_z_new = r_dot_z;
65  for (int k = 1; k <= Base::m_maxIterations; k++)
66  {
67  // temp = A*p
68  A.multiply(p, temp);
69  A.project(temp);
70  if (this->dot(p, temp) < 0)
71  {
72  if (verbose)
73  std::cout << "Encountered negative direction in CG!" << std::endl;
74  if (k == 1)
75  {
76  x = b;
77  }
78  return k;
79  }
80  // alpha = r^T * z / (p^T * A * p)
81  btScalar alpha = r_dot_z_new / this->dot(p, temp);
82  // x += alpha * p;
83  this->multAndAddTo(alpha, p, x);
84  // r -= alpha * temp;
85  this->multAndAddTo(-alpha, temp, r);
86  // z = M^(-1) * r
87  A.precondition(r, z);
88  r_dot_z = r_dot_z_new;
89  r_dot_z_new = this->dot(r, z);
90  if (r_dot_z_new < Base::m_tolerance * d0)
91  {
92  if (verbose)
93  {
94  std::cout << "ConjugateGradient iterations " << k << " residual = " << r_dot_z_new << std::endl;
95  }
96  return k;
97  }
98 
99  btScalar beta = r_dot_z_new / r_dot_z;
100  p = this->multAndAdd(beta, p, z);
101  }
102  if (verbose)
103  {
104  std::cout << "ConjugateGradient max iterations reached " << Base::m_maxIterations << " error = " << r_dot_z_new << std::endl;
105  }
106  return Base::m_maxIterations;
107  }
108 
109  void reinitialize(const TVStack& b)
110  {
111  r.resize(b.size());
112  p.resize(b.size());
113  z.resize(b.size());
114  temp.resize(b.size());
115  }
116 };
117 #endif /* btConjugateGradient_h */
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#define A
SIMD_FORCE_INLINE const T & btMin(const T &a, const T &b)
Definition: btMinMax.h:21
#define BT_PROFILE(name)
Definition: btQuickprof.h:198
float btScalar
The btScalar type abstracts floating point numbers, to easily switch between double and single floati...
Definition: btScalar.h:314
#define SIMD_EPSILON
Definition: btScalar.h:543
#define btAssert(x)
Definition: btScalar.h:295
static int verbose
Definition: cineonlib.c:29
SIMD_FORCE_INLINE void resize(int newsize, const T &fillData=T())
btConjugateGradient(const int max_it_in)
int solve(MatrixX &A, TVStack &x, const TVStack &b, bool verbose=false)
void reinitialize(const TVStack &b)
virtual SIMD_FORCE_INLINE TVStack sub(const TVStack &a, const TVStack &b)
virtual SIMD_FORCE_INLINE TVStack multAndAdd(btScalar s, const TVStack &a, const TVStack &b)
btScalar m_tolerance
virtual SIMD_FORCE_INLINE btScalar dot(const TVStack &a, const TVStack &b)
virtual SIMD_FORCE_INLINE void multAndAddTo(btScalar s, const TVStack &a, TVStack &result)
static const pxr::TfToken b("b", pxr::TfToken::Immortal)
ccl_device_inline float beta(float x, float y)
Definition: util/math.h:775