1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
|
// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2015 Gael Guennebaud <gael.guennebaud@inria.fr>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
#ifndef EIGEN_LEAST_SQUARE_CONJUGATE_GRADIENT_H
#define EIGEN_LEAST_SQUARE_CONJUGATE_GRADIENT_H
namespace Eigen {
namespace internal {
/** \internal Low-level conjugate gradient algorithm for least-square problems
* \param mat The matrix A
* \param rhs The right hand side vector b
* \param x On input and initial solution, on output the computed solution.
* \param precond A preconditioner being able to efficiently solve for an
* approximation of A'Ax=b (regardless of b)
* \param iters On input the max number of iteration, on output the number of performed iterations.
* \param tol_error On input the tolerance error, on output an estimation of the relative error.
*/
template<typename MatrixType, typename Rhs, typename Dest, typename Preconditioner>
EIGEN_DONT_INLINE
void least_square_conjugate_gradient(const MatrixType& mat, const Rhs& rhs, Dest& x,
const Preconditioner& precond, Index& iters,
typename Dest::RealScalar& tol_error)
{
using std::sqrt;
using std::abs;
typedef typename Dest::RealScalar RealScalar;
typedef typename Dest::Scalar Scalar;
typedef Matrix<Scalar,Dynamic,1> VectorType;
RealScalar tol = tol_error;
Index maxIters = iters;
Index m = mat.rows(), n = mat.cols();
VectorType residual = rhs - mat * x;
VectorType normal_residual = mat.adjoint() * residual;
RealScalar rhsNorm2 = (mat.adjoint()*rhs).squaredNorm();
if(rhsNorm2 == 0)
{
x.setZero();
iters = 0;
tol_error = 0;
return;
}
RealScalar threshold = tol*tol*rhsNorm2;
RealScalar residualNorm2 = normal_residual.squaredNorm();
if (residualNorm2 < threshold)
{
iters = 0;
tol_error = sqrt(residualNorm2 / rhsNorm2);
return;
}
VectorType p(n);
p = precond.solve(normal_residual); // initial search direction
VectorType z(n), tmp(m);
RealScalar absNew = numext::real(normal_residual.dot(p)); // the square of the absolute value of r scaled by invM
Index i = 0;
while(i < maxIters)
{
tmp.noalias() = mat * p;
Scalar alpha = absNew / tmp.squaredNorm(); // the amount we travel on dir
x += alpha * p; // update solution
residual -= alpha * tmp; // update residual
normal_residual = mat.adjoint() * residual; // update residual of the normal equation
residualNorm2 = normal_residual.squaredNorm();
if(residualNorm2 < threshold)
break;
z = precond.solve(normal_residual); // approximately solve for "A'A z = normal_residual"
RealScalar absOld = absNew;
absNew = numext::real(normal_residual.dot(z)); // update the absolute value of r
RealScalar beta = absNew / absOld; // calculate the Gram-Schmidt value used to create the new search direction
p = z + beta * p; // update search direction
i++;
}
tol_error = sqrt(residualNorm2 / rhsNorm2);
iters = i;
}
}
template< typename _MatrixType,
typename _Preconditioner = LeastSquareDiagonalPreconditioner<typename _MatrixType::Scalar> >
class LeastSquaresConjugateGradient;
namespace internal {
template< typename _MatrixType, typename _Preconditioner>
struct traits<LeastSquaresConjugateGradient<_MatrixType,_Preconditioner> >
{
typedef _MatrixType MatrixType;
typedef _Preconditioner Preconditioner;
};
}
/** \ingroup IterativeLinearSolvers_Module
* \brief A conjugate gradient solver for sparse (or dense) least-square problems
*
* This class allows to solve for A x = b linear problems using an iterative conjugate gradient algorithm.
* The matrix A can be non symmetric and rectangular, but the matrix A' A should be positive-definite to guaranty stability.
* Otherwise, the SparseLU or SparseQR classes might be preferable.
* The matrix A and the vectors x and b can be either dense or sparse.
*
* \tparam _MatrixType the type of the matrix A, can be a dense or a sparse matrix.
* \tparam _Preconditioner the type of the preconditioner. Default is LeastSquareDiagonalPreconditioner
*
* \implsparsesolverconcept
*
* The maximal number of iterations and tolerance value can be controlled via the setMaxIterations()
* and setTolerance() methods. The defaults are the size of the problem for the maximal number of iterations
* and NumTraits<Scalar>::epsilon() for the tolerance.
*
* This class can be used as the direct solver classes. Here is a typical usage example:
\code
int m=1000000, n = 10000;
VectorXd x(n), b(m);
SparseMatrix<double> A(m,n);
// fill A and b
LeastSquaresConjugateGradient<SparseMatrix<double> > lscg;
lscg.compute(A);
x = lscg.solve(b);
std::cout << "#iterations: " << lscg.iterations() << std::endl;
std::cout << "estimated error: " << lscg.error() << std::endl;
// update b, and solve again
x = lscg.solve(b);
\endcode
*
* By default the iterations start with x=0 as an initial guess of the solution.
* One can control the start using the solveWithGuess() method.
*
* \sa class ConjugateGradient, SparseLU, SparseQR
*/
template< typename _MatrixType, typename _Preconditioner>
class LeastSquaresConjugateGradient : public IterativeSolverBase<LeastSquaresConjugateGradient<_MatrixType,_Preconditioner> >
{
typedef IterativeSolverBase<LeastSquaresConjugateGradient> Base;
using Base::matrix;
using Base::m_error;
using Base::m_iterations;
using Base::m_info;
using Base::m_isInitialized;
public:
typedef _MatrixType MatrixType;
typedef typename MatrixType::Scalar Scalar;
typedef typename MatrixType::RealScalar RealScalar;
typedef _Preconditioner Preconditioner;
public:
/** Default constructor. */
LeastSquaresConjugateGradient() : Base() {}
/** Initialize the solver with matrix \a A for further \c Ax=b solving.
*
* This constructor is a shortcut for the default constructor followed
* by a call to compute().
*
* \warning this class stores a reference to the matrix A as well as some
* precomputed values that depend on it. Therefore, if \a A is changed
* this class becomes invalid. Call compute() to update it with the new
* matrix A, or modify a copy of A.
*/
template<typename MatrixDerived>
explicit LeastSquaresConjugateGradient(const EigenBase<MatrixDerived>& A) : Base(A.derived()) {}
~LeastSquaresConjugateGradient() {}
/** \internal */
template<typename Rhs,typename Dest>
void _solve_vector_with_guess_impl(const Rhs& b, Dest& x) const
{
m_iterations = Base::maxIterations();
m_error = Base::m_tolerance;
internal::least_square_conjugate_gradient(matrix(), b, x, Base::m_preconditioner, m_iterations, m_error);
m_info = m_error <= Base::m_tolerance ? Success : NoConvergence;
}
};
} // end namespace Eigen
#endif // EIGEN_LEAST_SQUARE_CONJUGATE_GRADIENT_H
|
