| /* linalg/bidiag.c |
| * |
| * Copyright (C) 2001 Brian Gough |
| * |
| * This program is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU General Public License as published by |
| * the Free Software Foundation; either version 2 of the License, or (at |
| * your option) any later version. |
| * |
| * This program is distributed in the hope that it will be useful, but |
| * WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| * General Public License for more details. |
| * |
| * You should have received a copy of the GNU General Public License |
| * along with this program; if not, write to the Free Software |
| * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. |
| */ |
| |
| /* Factorise a matrix A into |
| * |
| * A = U B V^T |
| * |
| * where U and V are orthogonal and B is upper bidiagonal. |
| * |
| * On exit, B is stored in the diagonal and first superdiagonal of A. |
| * |
| * U is stored as a packed set of Householder transformations in the |
| * lower triangular part of the input matrix below the diagonal. |
| * |
| * V is stored as a packed set of Householder transformations in the |
| * upper triangular part of the input matrix above the first |
| * superdiagonal. |
| * |
| * The full matrix for U can be obtained as the product |
| * |
| * U = U_1 U_2 .. U_N |
| * |
| * where |
| * |
| * U_i = (I - tau_i * u_i * u_i') |
| * |
| * and where u_i is a Householder vector |
| * |
| * u_i = [0, .. , 0, 1, A(i+1,i), A(i+3,i), .. , A(M,i)] |
| * |
| * The full matrix for V can be obtained as the product |
| * |
| * V = V_1 V_2 .. V_(N-2) |
| * |
| * where |
| * |
| * V_i = (I - tau_i * v_i * v_i') |
| * |
| * and where v_i is a Householder vector |
| * |
| * v_i = [0, .. , 0, 1, A(i,i+2), A(i,i+3), .. , A(i,N)] |
| * |
| * See Golub & Van Loan, "Matrix Computations" (3rd ed), Algorithm 5.4.2 |
| * |
| * Note: this description uses 1-based indices. The code below uses |
| * 0-based indices |
| */ |
| |
| #include <config.h> |
| #include <stdlib.h> |
| #include <gsl/gsl_math.h> |
| #include <gsl/gsl_vector.h> |
| #include <gsl/gsl_matrix.h> |
| #include <gsl/gsl_blas.h> |
| |
| #include <gsl/gsl_linalg.h> |
| |
| int |
| gsl_linalg_bidiag_decomp (gsl_matrix * A, gsl_vector * tau_U, gsl_vector * tau_V) |
| { |
| if (A->size1 < A->size2) |
| { |
| GSL_ERROR ("bidiagonal decomposition requires M>=N", GSL_EBADLEN); |
| } |
| else if (tau_U->size != A->size2) |
| { |
| GSL_ERROR ("size of tau_U must be N", GSL_EBADLEN); |
| } |
| else if (tau_V->size + 1 != A->size2) |
| { |
| GSL_ERROR ("size of tau_V must be (N - 1)", GSL_EBADLEN); |
| } |
| else |
| { |
| const size_t M = A->size1; |
| const size_t N = A->size2; |
| size_t i; |
| |
| for (i = 0 ; i < N; i++) |
| { |
| /* Apply Householder transformation to current column */ |
| |
| { |
| gsl_vector_view c = gsl_matrix_column (A, i); |
| gsl_vector_view v = gsl_vector_subvector (&c.vector, i, M - i); |
| double tau_i = gsl_linalg_householder_transform (&v.vector); |
| |
| /* Apply the transformation to the remaining columns */ |
| |
| if (i + 1 < N) |
| { |
| gsl_matrix_view m = |
| gsl_matrix_submatrix (A, i, i + 1, M - i, N - (i + 1)); |
| gsl_linalg_householder_hm (tau_i, &v.vector, &m.matrix); |
| } |
| |
| gsl_vector_set (tau_U, i, tau_i); |
| |
| } |
| |
| /* Apply Householder transformation to current row */ |
| |
| if (i + 1 < N) |
| { |
| gsl_vector_view r = gsl_matrix_row (A, i); |
| gsl_vector_view v = gsl_vector_subvector (&r.vector, i + 1, N - (i + 1)); |
| double tau_i = gsl_linalg_householder_transform (&v.vector); |
| |
| /* Apply the transformation to the remaining rows */ |
| |
| if (i + 1 < M) |
| { |
| gsl_matrix_view m = |
| gsl_matrix_submatrix (A, i+1, i+1, M - (i+1), N - (i+1)); |
| gsl_linalg_householder_mh (tau_i, &v.vector, &m.matrix); |
| } |
| |
| gsl_vector_set (tau_V, i, tau_i); |
| } |
| } |
| } |
| |
| return GSL_SUCCESS; |
| } |
| |
| /* Form the orthogonal matrices U, V, diagonal d and superdiagonal sd |
| from the packed bidiagonal matrix A */ |
| |
| int |
| gsl_linalg_bidiag_unpack (const gsl_matrix * A, |
| const gsl_vector * tau_U, |
| gsl_matrix * U, |
| const gsl_vector * tau_V, |
| gsl_matrix * V, |
| gsl_vector * diag, |
| gsl_vector * superdiag) |
| { |
| const size_t M = A->size1; |
| const size_t N = A->size2; |
| |
| const size_t K = GSL_MIN(M, N); |
| |
| if (M < N) |
| { |
| GSL_ERROR ("matrix A must have M >= N", GSL_EBADLEN); |
| } |
| else if (tau_U->size != K) |
| { |
| GSL_ERROR ("size of tau must be MIN(M,N)", GSL_EBADLEN); |
| } |
| else if (tau_V->size + 1 != K) |
| { |
| GSL_ERROR ("size of tau must be MIN(M,N) - 1", GSL_EBADLEN); |
| } |
| else if (U->size1 != M || U->size2 != N) |
| { |
| GSL_ERROR ("size of U must be M x N", GSL_EBADLEN); |
| } |
| else if (V->size1 != N || V->size2 != N) |
| { |
| GSL_ERROR ("size of V must be N x N", GSL_EBADLEN); |
| } |
| else if (diag->size != K) |
| { |
| GSL_ERROR ("size of diagonal must match size of A", GSL_EBADLEN); |
| } |
| else if (superdiag->size + 1 != K) |
| { |
| GSL_ERROR ("size of subdiagonal must be (diagonal size - 1)", GSL_EBADLEN); |
| } |
| else |
| { |
| size_t i, j; |
| |
| /* Copy diagonal into diag */ |
| |
| for (i = 0; i < N; i++) |
| { |
| double Aii = gsl_matrix_get (A, i, i); |
| gsl_vector_set (diag, i, Aii); |
| } |
| |
| /* Copy superdiagonal into superdiag */ |
| |
| for (i = 0; i < N - 1; i++) |
| { |
| double Aij = gsl_matrix_get (A, i, i+1); |
| gsl_vector_set (superdiag, i, Aij); |
| } |
| |
| /* Initialize V to the identity */ |
| |
| gsl_matrix_set_identity (V); |
| |
| for (i = N - 1; i > 0 && i--;) |
| { |
| /* Householder row transformation to accumulate V */ |
| gsl_vector_const_view r = gsl_matrix_const_row (A, i); |
| gsl_vector_const_view h = |
| gsl_vector_const_subvector (&r.vector, i + 1, N - (i+1)); |
| |
| double ti = gsl_vector_get (tau_V, i); |
| |
| gsl_matrix_view m = |
| gsl_matrix_submatrix (V, i + 1, i + 1, N-(i+1), N-(i+1)); |
| |
| gsl_linalg_householder_hm (ti, &h.vector, &m.matrix); |
| } |
| |
| /* Initialize U to the identity */ |
| |
| gsl_matrix_set_identity (U); |
| |
| for (j = N; j > 0 && j--;) |
| { |
| /* Householder column transformation to accumulate U */ |
| gsl_vector_const_view c = gsl_matrix_const_column (A, j); |
| gsl_vector_const_view h = gsl_vector_const_subvector (&c.vector, j, M - j); |
| double tj = gsl_vector_get (tau_U, j); |
| |
| gsl_matrix_view m = |
| gsl_matrix_submatrix (U, j, j, M-j, N-j); |
| |
| gsl_linalg_householder_hm (tj, &h.vector, &m.matrix); |
| } |
| |
| return GSL_SUCCESS; |
| } |
| } |
| |
| int |
| gsl_linalg_bidiag_unpack2 (gsl_matrix * A, |
| gsl_vector * tau_U, |
| gsl_vector * tau_V, |
| gsl_matrix * V) |
| { |
| const size_t M = A->size1; |
| const size_t N = A->size2; |
| |
| const size_t K = GSL_MIN(M, N); |
| |
| if (M < N) |
| { |
| GSL_ERROR ("matrix A must have M >= N", GSL_EBADLEN); |
| } |
| else if (tau_U->size != K) |
| { |
| GSL_ERROR ("size of tau must be MIN(M,N)", GSL_EBADLEN); |
| } |
| else if (tau_V->size + 1 != K) |
| { |
| GSL_ERROR ("size of tau must be MIN(M,N) - 1", GSL_EBADLEN); |
| } |
| else if (V->size1 != N || V->size2 != N) |
| { |
| GSL_ERROR ("size of V must be N x N", GSL_EBADLEN); |
| } |
| else |
| { |
| size_t i, j; |
| |
| /* Initialize V to the identity */ |
| |
| gsl_matrix_set_identity (V); |
| |
| for (i = N - 1; i > 0 && i--;) |
| { |
| /* Householder row transformation to accumulate V */ |
| gsl_vector_const_view r = gsl_matrix_const_row (A, i); |
| gsl_vector_const_view h = |
| gsl_vector_const_subvector (&r.vector, i + 1, N - (i+1)); |
| |
| double ti = gsl_vector_get (tau_V, i); |
| |
| gsl_matrix_view m = |
| gsl_matrix_submatrix (V, i + 1, i + 1, N-(i+1), N-(i+1)); |
| |
| gsl_linalg_householder_hm (ti, &h.vector, &m.matrix); |
| } |
| |
| /* Copy superdiagonal into tau_v */ |
| |
| for (i = 0; i < N - 1; i++) |
| { |
| double Aij = gsl_matrix_get (A, i, i+1); |
| gsl_vector_set (tau_V, i, Aij); |
| } |
| |
| /* Allow U to be unpacked into the same memory as A, copy |
| diagonal into tau_U */ |
| |
| for (j = N; j > 0 && j--;) |
| { |
| /* Householder column transformation to accumulate U */ |
| double tj = gsl_vector_get (tau_U, j); |
| double Ajj = gsl_matrix_get (A, j, j); |
| gsl_matrix_view m = gsl_matrix_submatrix (A, j, j, M-j, N-j); |
| |
| gsl_vector_set (tau_U, j, Ajj); |
| gsl_linalg_householder_hm1 (tj, &m.matrix); |
| } |
| |
| return GSL_SUCCESS; |
| } |
| } |
| |
| |
| int |
| gsl_linalg_bidiag_unpack_B (const gsl_matrix * A, |
| gsl_vector * diag, |
| gsl_vector * superdiag) |
| { |
| const size_t M = A->size1; |
| const size_t N = A->size2; |
| |
| const size_t K = GSL_MIN(M, N); |
| |
| if (diag->size != K) |
| { |
| GSL_ERROR ("size of diagonal must match size of A", GSL_EBADLEN); |
| } |
| else if (superdiag->size + 1 != K) |
| { |
| GSL_ERROR ("size of subdiagonal must be (matrix size - 1)", GSL_EBADLEN); |
| } |
| else |
| { |
| size_t i; |
| |
| /* Copy diagonal into diag */ |
| |
| for (i = 0; i < K; i++) |
| { |
| double Aii = gsl_matrix_get (A, i, i); |
| gsl_vector_set (diag, i, Aii); |
| } |
| |
| /* Copy superdiagonal into superdiag */ |
| |
| for (i = 0; i < K - 1; i++) |
| { |
| double Aij = gsl_matrix_get (A, i, i+1); |
| gsl_vector_set (superdiag, i, Aij); |
| } |
| |
| return GSL_SUCCESS; |
| } |
| } |