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  • 12/20/2021
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DSYEV 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. * ============================================================================= * * DSYEV Example. * ============== * * Program computes all eigenvalues and eigenvectors of a real symmetric * matrix A: * * 1.96 -6.49 -0.47 -7.20 -0.65 * -6.49 3.80 -6.39 1.50 -6.34 * -0.47 -6.39 4.17 -1.51 2.67 * -7.20 1.50 -1.51 5.70 1.80 * -0.65 -6.34 2.67 1.80 -7.10 * * Description. * ============ * * The routine computes all eigenvalues and, optionally, eigenvectors of an * n-by-n real symmetric matrix A. The eigenvector v(j) of A satisfies * * A*v(j) = lambda(j)*v(j) * * where lambda(j) is its eigenvalue. The computed eigenvectors are * orthonormal. * * Example Program Results. * ======================== * * DSYEV Example Program Results * * Eigenvalues * -11.07 -6.23 0.86 8.87 16.09 * * Eigenvectors (stored columnwise) * -0.30 -0.61 0.40 -0.37 0.49 * -0.51 -0.29 -0.41 -0.36 -0.61 * -0.08 -0.38 -0.66 0.50 0.40 * 0.00 -0.45 0.46 0.62 -0.46 * -0.80 0.45 0.17 0.31 0.16 * ============================================================================= * * .. Parameters .. INTEGER N PARAMETER ( N = 5 ) INTEGER LDA PARAMETER ( LDA = N ) INTEGER LWMAX PARAMETER ( LWMAX = 1000 ) * * .. Local Scalars .. INTEGER INFO, LWORK * * .. Local Arrays .. DOUBLE PRECISION A( LDA, N ), W( N ), WORK( LWMAX ) DATA A/ $ 1.96, 0.00, 0.00, 0.00, 0.00, $ -6.49, 3.80, 0.00, 0.00, 0.00, $ -0.47,-6.39, 4.17, 0.00, 0.00, $ -7.20, 1.50,-1.51, 5.70, 0.00, $ -0.65,-6.34, 2.67, 1.80,-7.10 $ / * * .. External Subroutines .. EXTERNAL DSYEV EXTERNAL PRINT_MATRIX * * .. Intrinsic Functions .. INTRINSIC INT, MIN * * .. Executable Statements .. WRITE(*,*)'DSYEV Example Program Results' * * Query the optimal workspace. * LWORK = -1 CALL DSYEV( 'Vectors', 'Upper', N, A, LDA, W, WORK, LWORK, INFO ) LWORK = MIN( LWMAX, INT( WORK( 1 ) ) ) * * Solve eigenproblem. * CALL DSYEV( 'Vectors', 'Upper', N, A, LDA, W, WORK, LWORK, INFO ) * * Check for convergence. * IF( INFO.GT.0 ) THEN WRITE(*,*)'The algorithm failed to compute eigenvalues.' STOP END IF * * Print eigenvalues. * CALL PRINT_MATRIX( 'Eigenvalues', 1, N, W, 1 ) * * Print eigenvectors. * CALL PRINT_MATRIX( 'Eigenvectors (stored columnwise)', N, N, A, $ LDA ) STOP END * * End of DSYEV Example. * * ============================================================================= * * Auxiliary routine: printing a matrix. * SUBROUTINE PRINT_MATRIX( DESC, M, N, A, LDA ) CHARACTER*(*) DESC INTEGER M, N, LDA DOUBLE PRECISION 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

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