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Intel® oneAPI Math Kernel Library LAPACK Examples

ID 766877
Date 10/31/2024
Public
Document Table of Contents

SSYSV Example Program in Fortran

* Copyright (C) 2009-2015 Intel Corporation. All Rights Reserved. * The information and material ("Material") provided below is owned by Intel * Corporation or its suppliers or licensors, and title to such Material remains * with Intel Corporation or its suppliers or licensors. The Material contains * proprietary information of Intel or its suppliers and licensors. The Material * is protected by worldwide copyright laws and treaty provisions. No part of * the Material may be copied, reproduced, published, uploaded, posted, * transmitted, or distributed in any way without Intel's prior express written * permission. No license under any patent, copyright or other intellectual * property rights in the Material is granted to or conferred upon you, either * expressly, by implication, inducement, estoppel or otherwise. Any license * under such intellectual property rights must be express and approved by Intel * in writing. * ============================================================================= * * SSYSV Example. * ============== * * The program computes the solution to the system of linear equations * with a real symmetric matrix A and multiple right-hand sides B, * where A is the coefficient matrix: * * -5.86 3.99 -5.93 -2.82 7.69 * 3.99 4.46 2.58 4.42 4.61 * -5.93 2.58 -8.52 8.57 7.69 * -2.82 4.42 8.57 3.72 8.07 * 7.69 4.61 7.69 8.07 9.83 * * and B is the right-hand side matrix: * * 1.32 -6.33 -8.77 * 2.22 1.69 -8.33 * 0.12 -1.56 9.54 * -6.41 -9.49 9.56 * 6.33 -3.67 7.48 * * Description. * ============ * * The routine solves for X the real system of linear equations A*X = B, * where A is an n-by-n symmetric matrix, the columns of matrix B are * individual right-hand sides, and the columns of X are the corresponding * solutions. * * The diagonal pivoting method is used to factor A as A = U*D*UT or * A = L*D*LT , where U (or L) is a product of permutation and unit upper * (lower) triangular matrices, and D is symmetric and block diagonal with * 1-by-1 and 2-by-2 diagonal blocks. * * The factored form of A is then used to solve the system of equations A*X = B. * * Example Program Results. * ======================== * * SSYSV Example Program Results * * Solution * 1.17 0.52 -0.86 * -0.71 1.05 -4.90 * -0.63 -0.52 0.99 * -0.33 0.43 1.22 * 0.83 -1.22 1.96 * * Details of factorization * -5.86 0.00 0.00 0.00 0.00 * -0.68 7.18 0.00 0.00 0.00 * 1.01 -0.20 -2.82 0.00 0.00 * 0.48 0.35 11.93 4.21 0.00 * -1.31 1.37 0.02 0.16 6.22 * * Pivot indices * 1 2 -4 -4 5 * ============================================================================= * * .. Parameters .. INTEGER N, NRHS PARAMETER ( N = 5, NRHS = 3 ) INTEGER LDA, LDB PARAMETER ( LDA = N, LDB = N ) INTEGER LWMAX PARAMETER ( LWMAX = 100 ) * * .. Local Scalars .. INTEGER INFO, LWORK * * .. Local Arrays .. INTEGER IPIV( N ) REAL A( LDA, N ), B( LDB, NRHS ), WORK( LWMAX ) DATA A/ $ -5.86, 3.99,-5.93,-2.82, 7.69, $ 0.00, 4.46, 2.58, 4.42, 4.61, $ 0.00, 0.00,-8.52, 8.57, 7.69, $ 0.00, 0.00, 0.00, 3.72, 8.07, $ 0.00, 0.00, 0.00, 0.00, 9.83 $ / DATA B/ $ 1.32, 2.22, 0.12,-6.41, 6.33, $ -6.33, 1.69,-1.56,-9.49,-3.67, $ -8.77,-8.33, 9.54, 9.56, 7.48 $ / * * .. External Subroutines .. EXTERNAL SSYSV EXTERNAL PRINT_MATRIX, PRINT_INT_VECTOR * * .. Intrinsic Functions .. INTRINSIC INT, MIN * * .. Executable Statements .. WRITE(*,*)'SSYSV Example Program Results' * * Query the optimal workspace. * LWORK = -1 CALL SSYSV( 'Lower', N, NRHS, A, LDA, IPIV, B, LDB, WORK, LWORK, $ INFO ) LWORK = MIN( LWMAX, INT( WORK( 1 ) ) ) * * Solve the equations A*X = B. * CALL SSYSV( 'Lower', N, NRHS, A, LDA, IPIV, B, LDB, WORK, LWORK, $ INFO ) * * Check for the exact singularity. * IF( INFO.GT.0 ) THEN WRITE(*,*)'The element of the diagonal factor ' WRITE(*,*)'D(',INFO,',',INFO,') is zero, so that' WRITE(*,*)'D is singular; the solution could not be computed.' STOP END IF * * Print solution. * CALL PRINT_MATRIX( 'Solution', N, NRHS, B, LDB ) * * Print details of factorization. * CALL PRINT_MATRIX( 'Details of factorization', N, N, A, LDA ) * * Print pivot indices. * CALL PRINT_INT_VECTOR( 'Pivot indices', N, IPIV ) STOP END * * End of SSYSV Example. * * ============================================================================= * * Auxiliary routine: printing a matrix. * SUBROUTINE PRINT_MATRIX( DESC, M, N, A, LDA ) CHARACTER*(*) DESC INTEGER M, N, LDA REAL A( LDA, * ) * INTEGER I, J * WRITE(*,*) WRITE(*,*) DESC DO I = 1, M WRITE(*,9998) ( A( I, J ), J = 1, N ) END DO * 9998 FORMAT( 11(:,1X,F6.2) ) RETURN END * * Auxiliary routine: printing a vector of integers. * SUBROUTINE PRINT_INT_VECTOR( DESC, N, A ) CHARACTER*(*) DESC INTEGER N INTEGER A( N ) * INTEGER I * WRITE(*,*) WRITE(*,*) DESC WRITE(*,9999) ( A( I ), I = 1, N ) * 9999 FORMAT( 11(:,1X,I6) ) RETURN END