Developer Reference

ID 766877
Date 12/20/2021
Public

## DSYEVD 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
*  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.
*  =============================================================================
*
*  DSYEVD Example.
*  ==============
*
*  Program computes all eigenvalues and eigenvectors of a real symmetric
*  matrix A using divide and conquer algorithm, where A is:
*
*    6.39   0.13  -8.23   5.71  -3.18
*    0.13   8.37  -4.46  -6.10   7.21
*   -8.23  -4.46  -9.58  -9.25  -7.42
*    5.71  -6.10  -9.25   3.72   8.54
*   -3.18   7.21  -7.42   8.54   2.51
*
*  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.
*  If the eigenvectors are requested, then this routine uses a divide and
*  conquer algorithm to compute eigenvalues and eigenvectors.
*
*  Example Program Results.
*  ========================
*
* DSYEVD Example Program Results
*
* Eigenvalues
* -17.44 -11.96   6.72  14.25  19.84
*
* Eigenvectors (stored columnwise)
*  -0.26   0.31  -0.74   0.33   0.42
*  -0.17  -0.39  -0.38  -0.80   0.16
*  -0.89   0.04   0.09   0.03  -0.45
*  -0.29  -0.59   0.34   0.31   0.60
*  -0.19   0.63   0.44  -0.38   0.48
*  =============================================================================
*
*     .. Parameters ..
INTEGER          N
PARAMETER        ( N = 5 )
INTEGER          LDA
PARAMETER        ( LDA = N )
INTEGER          LWMAX
PARAMETER        ( LWMAX = 1000 )
*
*     .. Local Scalars ..
INTEGER          INFO, LWORK, LIWORK
*
*     .. Local Arrays ..
INTEGER          IWORK( LWMAX )
DOUBLE PRECISION A( LDA, N ), W( N ), WORK( LWMAX )
DATA             A/
$6.39, 0.00, 0.00, 0.00, 0.00,$  0.13, 8.37, 0.00, 0.00, 0.00,
$-8.23,-4.46,-9.58, 0.00, 0.00,$  5.71,-6.10,-9.25, 3.72, 0.00,
$-3.18, 7.21,-7.42, 8.54, 2.51$                  /
*
*     .. External Subroutines ..
EXTERNAL         DSYEVD
EXTERNAL         PRINT_MATRIX
*
*     .. Intrinsic Functions ..
INTRINSIC        INT, MIN
*
*     .. Executable Statements ..
WRITE(*,*)'DSYEVD Example Program Results'
*
*     Query the optimal workspace.
*
LWORK = -1
LIWORK = -1
CALL DSYEVD( 'Vectors', 'Upper', N, A, LDA, W, WORK, LWORK,
$IWORK, LIWORK, INFO ) LWORK = MIN( LWMAX, INT( WORK( 1 ) ) ) LIWORK = MIN( LWMAX, IWORK( 1 ) ) * * Solve eigenproblem. * CALL DSYEVD( 'Vectors', 'Upper', N, A, LDA, W, WORK, LWORK,$             IWORK, LIWORK, 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 DSYEVD 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