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ZGEEV Example Program in Fortran
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* =============================================================================
*
* ZGEEV Example.
* ==============
*
* Program computes the eigenvalues and left and right eigenvectors of a general
* rectangular matrix A:
*
* ( -3.84, 2.25) ( -8.94, -4.75) ( 8.95, -6.53) ( -9.87, 4.82)
* ( -0.66, 0.83) ( -4.40, -3.82) ( -3.50, -4.26) ( -3.15, 7.36)
* ( -3.99, -4.73) ( -5.88, -6.60) ( -3.36, -0.40) ( -0.75, 5.23)
* ( 7.74, 4.18) ( 3.66, -7.53) ( 2.58, 3.60) ( 4.59, 5.41)
*
* Description.
* ============
*
* The routine computes for an n-by-n complex nonsymmetric matrix A, the
* eigenvalues and, optionally, the left and/or right eigenvectors. The right
* eigenvector v(j) of A satisfies
*
* A*v(j)= lambda(j)*v(j)
*
* where lambda(j) is its eigenvalue. The left eigenvector u(j) of A satisfies
*
* u(j)H*A = lambda(j)*u(j)H
*
* where u(j)H denotes the conjugate transpose of u(j). The computed
* eigenvectors are normalized to have Euclidean norm equal to 1 and
* largest component real.
*
* Example Program Results.
* ========================
*
* ZGEEV Example Program Results
*
* Eigenvalues
* ( -9.43,-12.98) ( -3.44, 12.69) ( 0.11, -3.40) ( 5.76, 7.13)
*
* Left eigenvectors
* ( 0.24, -0.18) ( 0.61, 0.00) ( -0.18, -0.33) ( 0.28, 0.09)
* ( 0.79, 0.00) ( -0.05, -0.27) ( 0.82, 0.00) ( -0.55, 0.16)
* ( 0.22, -0.27) ( -0.21, 0.53) ( -0.37, 0.15) ( 0.45, 0.09)
* ( -0.02, 0.41) ( 0.40, -0.24) ( 0.06, 0.12) ( 0.62, 0.00)
*
* Right eigenvectors
* ( 0.43, 0.33) ( 0.83, 0.00) ( 0.60, 0.00) ( -0.31, 0.03)
* ( 0.51, -0.03) ( 0.08, -0.25) ( -0.40, -0.20) ( 0.04, 0.34)
* ( 0.62, 0.00) ( -0.25, 0.28) ( -0.09, -0.48) ( 0.36, 0.06)
* ( -0.23, 0.11) ( -0.10, -0.32) ( -0.43, 0.13) ( 0.81, 0.00)
* =============================================================================
*
* .. Parameters ..
INTEGER N
PARAMETER ( N = 4 )
INTEGER LDA, LDVL, LDVR
PARAMETER ( LDA = N, LDVL = N, LDVR = N )
INTEGER LWMAX
PARAMETER ( LWMAX = 1000 )
*
* .. Local Scalars ..
INTEGER INFO, LWORK
*
* .. Local Arrays ..
* RWORK dimension should be at least 2*N
DOUBLE PRECISION RWORK( 2*N )
COMPLEX*16 A( LDA, N ), VL( LDVL, N ), VR( LDVR, N ),
$ W( N ), WORK( LWMAX )
DATA A/
$ (-3.84, 2.25),(-0.66, 0.83),(-3.99,-4.73),( 7.74, 4.18),
$ (-8.94,-4.75),(-4.40,-3.82),(-5.88,-6.60),( 3.66,-7.53),
$ ( 8.95,-6.53),(-3.50,-4.26),(-3.36,-0.40),( 2.58, 3.60),
$ (-9.87, 4.82),(-3.15, 7.36),(-0.75, 5.23),( 4.59, 5.41)
$ /
*
* .. External Subroutines ..
EXTERNAL ZGEEV
EXTERNAL PRINT_MATRIX
*
* .. Intrinsic Functions ..
INTRINSIC INT, MIN
*
* .. Executable Statements ..
WRITE(*,*)'ZGEEV Example Program Results'
*
* Query the optimal workspace.
*
LWORK = -1
CALL ZGEEV( 'Vectors', 'Vectors', N, A, LDA, W, VL, LDVL,
$ VR, LDVR, WORK, LWORK, RWORK, INFO )
LWORK = MIN( LWMAX, INT( WORK( 1 ) ) )
*
* Solve eigenproblem.
*
CALL ZGEEV( 'Vectors', 'Vectors', N, A, LDA, W, VL, LDVL,
$ VR, LDVR, WORK, LWORK, RWORK, 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 left eigenvectors.
*
CALL PRINT_MATRIX( 'Left eigenvectors', N, N, VL, LDVL )
*
* Print right eigenvectors.
*
CALL PRINT_MATRIX( 'Right eigenvectors', N, N, VR, LDVR )
STOP
END
*
* End of ZGEEV Example.
*
* =============================================================================
*
* Auxiliary routine: printing a matrix.
*
SUBROUTINE PRINT_MATRIX( DESC, M, N, A, LDA )
CHARACTER*(*) DESC
INTEGER M, N, LDA
COMPLEX*16 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,',',F6.2,')') )
RETURN
END
Parent topic: ZGEEV Example