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-// 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_with_guess_impl(const Rhs& b, Dest& x) const
- {
- m_iterations = Base::maxIterations();
- m_error = Base::m_tolerance;
-
- for(Index j=0; j<b.cols(); ++j)
- {
- m_iterations = Base::maxIterations();
- m_error = Base::m_tolerance;
-
- typename Dest::ColXpr xj(x,j);
- internal::least_square_conjugate_gradient(matrix(), b.col(j), xj, Base::m_preconditioner, m_iterations, m_error);
- }
-
- m_isInitialized = true;
- m_info = m_error <= Base::m_tolerance ? Success : NoConvergence;
- }
-
- /** \internal */
- using Base::_solve_impl;
- template<typename Rhs,typename Dest>
- void _solve_impl(const MatrixBase<Rhs>& b, Dest& x) const
- {
- x.setZero();
- _solve_with_guess_impl(b.derived(),x);
- }
-
-};
-
-} // end namespace Eigen
-
-#endif // EIGEN_LEAST_SQUARE_CONJUGATE_GRADIENT_H