## Developer Reference

• 2022.1
• 12/20/2021
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Contents

# SSYEV 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.
*  =============================================================================
*
*  SSYEV 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.
*  ========================
*
* SSYEV 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 ..
REAL             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         SSYEV
EXTERNAL         PRINT_MATRIX
*
*     .. Intrinsic Functions ..
INTRINSIC        INT, MIN
*
*     .. Executable Statements ..
WRITE(*,*)'SSYEV Example Program Results'
*
*     Query the optimal workspace.
*
LWORK = -1
CALL SSYEV( 'Vectors', 'Upper', N, A, LDA, W, WORK, LWORK, INFO )
LWORK = MIN( LWMAX, INT( WORK( 1 ) ) )
*
*     Solve eigenproblem.
*
CALL SSYEV( '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 SSYEV 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``````

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