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Diffstat (limited to 'unsupported/Eigen/src/MatrixFunctions/MatrixSquareRoot.h')
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diff --git a/unsupported/Eigen/src/MatrixFunctions/MatrixSquareRoot.h b/unsupported/Eigen/src/MatrixFunctions/MatrixSquareRoot.h new file mode 100644 index 000000000..10319fa17 --- /dev/null +++ b/unsupported/Eigen/src/MatrixFunctions/MatrixSquareRoot.h @@ -0,0 +1,484 @@ +// This file is part of Eigen, a lightweight C++ template library +// for linear algebra. +// +// Copyright (C) 2011 Jitse Niesen <jitse@maths.leeds.ac.uk> +// +// 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_MATRIX_SQUARE_ROOT +#define EIGEN_MATRIX_SQUARE_ROOT + +namespace Eigen { + +/** \ingroup MatrixFunctions_Module + * \brief Class for computing matrix square roots of upper quasi-triangular matrices. + * \tparam MatrixType type of the argument of the matrix square root, + * expected to be an instantiation of the Matrix class template. + * + * This class computes the square root of the upper quasi-triangular + * matrix stored in the upper Hessenberg part of the matrix passed to + * the constructor. + * + * \sa MatrixSquareRoot, MatrixSquareRootTriangular + */ +template <typename MatrixType> +class MatrixSquareRootQuasiTriangular +{ + public: + + /** \brief Constructor. + * + * \param[in] A upper quasi-triangular matrix whose square root + * is to be computed. + * + * The class stores a reference to \p A, so it should not be + * changed (or destroyed) before compute() is called. + */ + MatrixSquareRootQuasiTriangular(const MatrixType& A) + : m_A(A) + { + eigen_assert(A.rows() == A.cols()); + } + + /** \brief Compute the matrix square root + * + * \param[out] result square root of \p A, as specified in the constructor. + * + * Only the upper Hessenberg part of \p result is updated, the + * rest is not touched. See MatrixBase::sqrt() for details on + * how this computation is implemented. + */ + template <typename ResultType> void compute(ResultType &result); + + private: + typedef typename MatrixType::Index Index; + typedef typename MatrixType::Scalar Scalar; + + void computeDiagonalPartOfSqrt(MatrixType& sqrtT, const MatrixType& T); + void computeOffDiagonalPartOfSqrt(MatrixType& sqrtT, const MatrixType& T); + void compute2x2diagonalBlock(MatrixType& sqrtT, const MatrixType& T, typename MatrixType::Index i); + void compute1x1offDiagonalBlock(MatrixType& sqrtT, const MatrixType& T, + typename MatrixType::Index i, typename MatrixType::Index j); + void compute1x2offDiagonalBlock(MatrixType& sqrtT, const MatrixType& T, + typename MatrixType::Index i, typename MatrixType::Index j); + void compute2x1offDiagonalBlock(MatrixType& sqrtT, const MatrixType& T, + typename MatrixType::Index i, typename MatrixType::Index j); + void compute2x2offDiagonalBlock(MatrixType& sqrtT, const MatrixType& T, + typename MatrixType::Index i, typename MatrixType::Index j); + + template <typename SmallMatrixType> + static void solveAuxiliaryEquation(SmallMatrixType& X, const SmallMatrixType& A, + const SmallMatrixType& B, const SmallMatrixType& C); + + const MatrixType& m_A; +}; + +template <typename MatrixType> +template <typename ResultType> +void MatrixSquareRootQuasiTriangular<MatrixType>::compute(ResultType &result) +{ + // Compute Schur decomposition of m_A + const RealSchur<MatrixType> schurOfA(m_A); + const MatrixType& T = schurOfA.matrixT(); + const MatrixType& U = schurOfA.matrixU(); + + // Compute square root of T + MatrixType sqrtT = MatrixType::Zero(m_A.rows(), m_A.rows()); + computeDiagonalPartOfSqrt(sqrtT, T); + computeOffDiagonalPartOfSqrt(sqrtT, T); + + // Compute square root of m_A + result = U * sqrtT * U.adjoint(); +} + +// pre: T is quasi-upper-triangular and sqrtT is a zero matrix of the same size +// post: the diagonal blocks of sqrtT are the square roots of the diagonal blocks of T +template <typename MatrixType> +void MatrixSquareRootQuasiTriangular<MatrixType>::computeDiagonalPartOfSqrt(MatrixType& sqrtT, + const MatrixType& T) +{ + const Index size = m_A.rows(); + for (Index i = 0; i < size; i++) { + if (i == size - 1 || T.coeff(i+1, i) == 0) { + eigen_assert(T(i,i) > 0); + sqrtT.coeffRef(i,i) = internal::sqrt(T.coeff(i,i)); + } + else { + compute2x2diagonalBlock(sqrtT, T, i); + ++i; + } + } +} + +// pre: T is quasi-upper-triangular and diagonal blocks of sqrtT are square root of diagonal blocks of T. +// post: sqrtT is the square root of T. +template <typename MatrixType> +void MatrixSquareRootQuasiTriangular<MatrixType>::computeOffDiagonalPartOfSqrt(MatrixType& sqrtT, + const MatrixType& T) +{ + const Index size = m_A.rows(); + for (Index j = 1; j < size; j++) { + if (T.coeff(j, j-1) != 0) // if T(j-1:j, j-1:j) is a 2-by-2 block + continue; + for (Index i = j-1; i >= 0; i--) { + if (i > 0 && T.coeff(i, i-1) != 0) // if T(i-1:i, i-1:i) is a 2-by-2 block + continue; + bool iBlockIs2x2 = (i < size - 1) && (T.coeff(i+1, i) != 0); + bool jBlockIs2x2 = (j < size - 1) && (T.coeff(j+1, j) != 0); + if (iBlockIs2x2 && jBlockIs2x2) + compute2x2offDiagonalBlock(sqrtT, T, i, j); + else if (iBlockIs2x2 && !jBlockIs2x2) + compute2x1offDiagonalBlock(sqrtT, T, i, j); + else if (!iBlockIs2x2 && jBlockIs2x2) + compute1x2offDiagonalBlock(sqrtT, T, i, j); + else if (!iBlockIs2x2 && !jBlockIs2x2) + compute1x1offDiagonalBlock(sqrtT, T, i, j); + } + } +} + +// pre: T.block(i,i,2,2) has complex conjugate eigenvalues +// post: sqrtT.block(i,i,2,2) is square root of T.block(i,i,2,2) +template <typename MatrixType> +void MatrixSquareRootQuasiTriangular<MatrixType> + ::compute2x2diagonalBlock(MatrixType& sqrtT, const MatrixType& T, typename MatrixType::Index i) +{ + // TODO: This case (2-by-2 blocks with complex conjugate eigenvalues) is probably hidden somewhere + // in EigenSolver. If we expose it, we could call it directly from here. + Matrix<Scalar,2,2> block = T.template block<2,2>(i,i); + EigenSolver<Matrix<Scalar,2,2> > es(block); + sqrtT.template block<2,2>(i,i) + = (es.eigenvectors() * es.eigenvalues().cwiseSqrt().asDiagonal() * es.eigenvectors().inverse()).real(); +} + +// pre: block structure of T is such that (i,j) is a 1x1 block, +// all blocks of sqrtT to left of and below (i,j) are correct +// post: sqrtT(i,j) has the correct value +template <typename MatrixType> +void MatrixSquareRootQuasiTriangular<MatrixType> + ::compute1x1offDiagonalBlock(MatrixType& sqrtT, const MatrixType& T, + typename MatrixType::Index i, typename MatrixType::Index j) +{ + Scalar tmp = (sqrtT.row(i).segment(i+1,j-i-1) * sqrtT.col(j).segment(i+1,j-i-1)).value(); + sqrtT.coeffRef(i,j) = (T.coeff(i,j) - tmp) / (sqrtT.coeff(i,i) + sqrtT.coeff(j,j)); +} + +// similar to compute1x1offDiagonalBlock() +template <typename MatrixType> +void MatrixSquareRootQuasiTriangular<MatrixType> + ::compute1x2offDiagonalBlock(MatrixType& sqrtT, const MatrixType& T, + typename MatrixType::Index i, typename MatrixType::Index j) +{ + Matrix<Scalar,1,2> rhs = T.template block<1,2>(i,j); + if (j-i > 1) + rhs -= sqrtT.block(i, i+1, 1, j-i-1) * sqrtT.block(i+1, j, j-i-1, 2); + Matrix<Scalar,2,2> A = sqrtT.coeff(i,i) * Matrix<Scalar,2,2>::Identity(); + A += sqrtT.template block<2,2>(j,j).transpose(); + sqrtT.template block<1,2>(i,j).transpose() = A.fullPivLu().solve(rhs.transpose()); +} + +// similar to compute1x1offDiagonalBlock() +template <typename MatrixType> +void MatrixSquareRootQuasiTriangular<MatrixType> + ::compute2x1offDiagonalBlock(MatrixType& sqrtT, const MatrixType& T, + typename MatrixType::Index i, typename MatrixType::Index j) +{ + Matrix<Scalar,2,1> rhs = T.template block<2,1>(i,j); + if (j-i > 2) + rhs -= sqrtT.block(i, i+2, 2, j-i-2) * sqrtT.block(i+2, j, j-i-2, 1); + Matrix<Scalar,2,2> A = sqrtT.coeff(j,j) * Matrix<Scalar,2,2>::Identity(); + A += sqrtT.template block<2,2>(i,i); + sqrtT.template block<2,1>(i,j) = A.fullPivLu().solve(rhs); +} + +// similar to compute1x1offDiagonalBlock() +template <typename MatrixType> +void MatrixSquareRootQuasiTriangular<MatrixType> + ::compute2x2offDiagonalBlock(MatrixType& sqrtT, const MatrixType& T, + typename MatrixType::Index i, typename MatrixType::Index j) +{ + Matrix<Scalar,2,2> A = sqrtT.template block<2,2>(i,i); + Matrix<Scalar,2,2> B = sqrtT.template block<2,2>(j,j); + Matrix<Scalar,2,2> C = T.template block<2,2>(i,j); + if (j-i > 2) + C -= sqrtT.block(i, i+2, 2, j-i-2) * sqrtT.block(i+2, j, j-i-2, 2); + Matrix<Scalar,2,2> X; + solveAuxiliaryEquation(X, A, B, C); + sqrtT.template block<2,2>(i,j) = X; +} + +// solves the equation A X + X B = C where all matrices are 2-by-2 +template <typename MatrixType> +template <typename SmallMatrixType> +void MatrixSquareRootQuasiTriangular<MatrixType> + ::solveAuxiliaryEquation(SmallMatrixType& X, const SmallMatrixType& A, + const SmallMatrixType& B, const SmallMatrixType& C) +{ + EIGEN_STATIC_ASSERT((internal::is_same<SmallMatrixType, Matrix<Scalar,2,2> >::value), + EIGEN_INTERNAL_ERROR_PLEASE_FILE_A_BUG_REPORT); + + Matrix<Scalar,4,4> coeffMatrix = Matrix<Scalar,4,4>::Zero(); + coeffMatrix.coeffRef(0,0) = A.coeff(0,0) + B.coeff(0,0); + coeffMatrix.coeffRef(1,1) = A.coeff(0,0) + B.coeff(1,1); + coeffMatrix.coeffRef(2,2) = A.coeff(1,1) + B.coeff(0,0); + coeffMatrix.coeffRef(3,3) = A.coeff(1,1) + B.coeff(1,1); + coeffMatrix.coeffRef(0,1) = B.coeff(1,0); + coeffMatrix.coeffRef(0,2) = A.coeff(0,1); + coeffMatrix.coeffRef(1,0) = B.coeff(0,1); + coeffMatrix.coeffRef(1,3) = A.coeff(0,1); + coeffMatrix.coeffRef(2,0) = A.coeff(1,0); + coeffMatrix.coeffRef(2,3) = B.coeff(1,0); + coeffMatrix.coeffRef(3,1) = A.coeff(1,0); + coeffMatrix.coeffRef(3,2) = B.coeff(0,1); + + Matrix<Scalar,4,1> rhs; + rhs.coeffRef(0) = C.coeff(0,0); + rhs.coeffRef(1) = C.coeff(0,1); + rhs.coeffRef(2) = C.coeff(1,0); + rhs.coeffRef(3) = C.coeff(1,1); + + Matrix<Scalar,4,1> result; + result = coeffMatrix.fullPivLu().solve(rhs); + + X.coeffRef(0,0) = result.coeff(0); + X.coeffRef(0,1) = result.coeff(1); + X.coeffRef(1,0) = result.coeff(2); + X.coeffRef(1,1) = result.coeff(3); +} + + +/** \ingroup MatrixFunctions_Module + * \brief Class for computing matrix square roots of upper triangular matrices. + * \tparam MatrixType type of the argument of the matrix square root, + * expected to be an instantiation of the Matrix class template. + * + * This class computes the square root of the upper triangular matrix + * stored in the upper triangular part (including the diagonal) of + * the matrix passed to the constructor. + * + * \sa MatrixSquareRoot, MatrixSquareRootQuasiTriangular + */ +template <typename MatrixType> +class MatrixSquareRootTriangular +{ + public: + MatrixSquareRootTriangular(const MatrixType& A) + : m_A(A) + { + eigen_assert(A.rows() == A.cols()); + } + + /** \brief Compute the matrix square root + * + * \param[out] result square root of \p A, as specified in the constructor. + * + * Only the upper triangular part (including the diagonal) of + * \p result is updated, the rest is not touched. See + * MatrixBase::sqrt() for details on how this computation is + * implemented. + */ + template <typename ResultType> void compute(ResultType &result); + + private: + const MatrixType& m_A; +}; + +template <typename MatrixType> +template <typename ResultType> +void MatrixSquareRootTriangular<MatrixType>::compute(ResultType &result) +{ + // Compute Schur decomposition of m_A + const ComplexSchur<MatrixType> schurOfA(m_A); + const MatrixType& T = schurOfA.matrixT(); + const MatrixType& U = schurOfA.matrixU(); + + // Compute square root of T and store it in upper triangular part of result + // This uses that the square root of triangular matrices can be computed directly. + result.resize(m_A.rows(), m_A.cols()); + typedef typename MatrixType::Index Index; + for (Index i = 0; i < m_A.rows(); i++) { + result.coeffRef(i,i) = internal::sqrt(T.coeff(i,i)); + } + for (Index j = 1; j < m_A.cols(); j++) { + for (Index i = j-1; i >= 0; i--) { + typedef typename MatrixType::Scalar Scalar; + // if i = j-1, then segment has length 0 so tmp = 0 + Scalar tmp = (result.row(i).segment(i+1,j-i-1) * result.col(j).segment(i+1,j-i-1)).value(); + // denominator may be zero if original matrix is singular + result.coeffRef(i,j) = (T.coeff(i,j) - tmp) / (result.coeff(i,i) + result.coeff(j,j)); + } + } + + // Compute square root of m_A as U * result * U.adjoint() + MatrixType tmp; + tmp.noalias() = U * result.template triangularView<Upper>(); + result.noalias() = tmp * U.adjoint(); +} + + +/** \ingroup MatrixFunctions_Module + * \brief Class for computing matrix square roots of general matrices. + * \tparam MatrixType type of the argument of the matrix square root, + * expected to be an instantiation of the Matrix class template. + * + * \sa MatrixSquareRootTriangular, MatrixSquareRootQuasiTriangular, MatrixBase::sqrt() + */ +template <typename MatrixType, int IsComplex = NumTraits<typename internal::traits<MatrixType>::Scalar>::IsComplex> +class MatrixSquareRoot +{ + public: + + /** \brief Constructor. + * + * \param[in] A matrix whose square root is to be computed. + * + * The class stores a reference to \p A, so it should not be + * changed (or destroyed) before compute() is called. + */ + MatrixSquareRoot(const MatrixType& A); + + /** \brief Compute the matrix square root + * + * \param[out] result square root of \p A, as specified in the constructor. + * + * See MatrixBase::sqrt() for details on how this computation is + * implemented. + */ + template <typename ResultType> void compute(ResultType &result); +}; + + +// ********** Partial specialization for real matrices ********** + +template <typename MatrixType> +class MatrixSquareRoot<MatrixType, 0> +{ + public: + + MatrixSquareRoot(const MatrixType& A) + : m_A(A) + { + eigen_assert(A.rows() == A.cols()); + } + + template <typename ResultType> void compute(ResultType &result) + { + // Compute Schur decomposition of m_A + const RealSchur<MatrixType> schurOfA(m_A); + const MatrixType& T = schurOfA.matrixT(); + const MatrixType& U = schurOfA.matrixU(); + + // Compute square root of T + MatrixSquareRootQuasiTriangular<MatrixType> tmp(T); + MatrixType sqrtT = MatrixType::Zero(m_A.rows(), m_A.rows()); + tmp.compute(sqrtT); + + // Compute square root of m_A + result = U * sqrtT * U.adjoint(); + } + + private: + const MatrixType& m_A; +}; + + +// ********** Partial specialization for complex matrices ********** + +template <typename MatrixType> +class MatrixSquareRoot<MatrixType, 1> +{ + public: + + MatrixSquareRoot(const MatrixType& A) + : m_A(A) + { + eigen_assert(A.rows() == A.cols()); + } + + template <typename ResultType> void compute(ResultType &result) + { + // Compute Schur decomposition of m_A + const ComplexSchur<MatrixType> schurOfA(m_A); + const MatrixType& T = schurOfA.matrixT(); + const MatrixType& U = schurOfA.matrixU(); + + // Compute square root of T + MatrixSquareRootTriangular<MatrixType> tmp(T); + MatrixType sqrtT = MatrixType::Zero(m_A.rows(), m_A.rows()); + tmp.compute(sqrtT); + + // Compute square root of m_A + result = U * sqrtT * U.adjoint(); + } + + private: + const MatrixType& m_A; +}; + + +/** \ingroup MatrixFunctions_Module + * + * \brief Proxy for the matrix square root of some matrix (expression). + * + * \tparam Derived Type of the argument to the matrix square root. + * + * This class holds the argument to the matrix square root until it + * is assigned or evaluated for some other reason (so the argument + * should not be changed in the meantime). It is the return type of + * MatrixBase::sqrt() and most of the time this is the only way it is + * used. + */ +template<typename Derived> class MatrixSquareRootReturnValue +: public ReturnByValue<MatrixSquareRootReturnValue<Derived> > +{ + typedef typename Derived::Index Index; + public: + /** \brief Constructor. + * + * \param[in] src %Matrix (expression) forming the argument of the + * matrix square root. + */ + MatrixSquareRootReturnValue(const Derived& src) : m_src(src) { } + + /** \brief Compute the matrix square root. + * + * \param[out] result the matrix square root of \p src in the + * constructor. + */ + template <typename ResultType> + inline void evalTo(ResultType& result) const + { + const typename Derived::PlainObject srcEvaluated = m_src.eval(); + MatrixSquareRoot<typename Derived::PlainObject> me(srcEvaluated); + me.compute(result); + } + + Index rows() const { return m_src.rows(); } + Index cols() const { return m_src.cols(); } + + protected: + const Derived& m_src; + private: + MatrixSquareRootReturnValue& operator=(const MatrixSquareRootReturnValue&); +}; + +namespace internal { +template<typename Derived> +struct traits<MatrixSquareRootReturnValue<Derived> > +{ + typedef typename Derived::PlainObject ReturnType; +}; +} + +template <typename Derived> +const MatrixSquareRootReturnValue<Derived> MatrixBase<Derived>::sqrt() const +{ + eigen_assert(rows() == cols()); + return MatrixSquareRootReturnValue<Derived>(derived()); +} + +} // end namespace Eigen + +#endif // EIGEN_MATRIX_FUNCTION |