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CHEEVD Example Program in Fortran
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* =============================================================================
*
* CHEEVD Example.
* ==============
*
* Program computes all eigenvalues and eigenvectors of a complex Hermitian
* matrix A using divide and conquer algorithm, where A is:
*
* ( 3.40, 0.00) ( -2.36, -1.93) ( -4.68, 9.55) ( 5.37, -1.23)
* ( -2.36, 1.93) ( 6.94, 0.00) ( 8.13, -1.47) ( 2.07, -5.78)
* ( -4.68, -9.55) ( 8.13, 1.47) ( -2.14, 0.00) ( 4.68, 7.44)
* ( 5.37, 1.23) ( 2.07, 5.78) ( 4.68, -7.44) ( -7.42, 0.00)
*
* Description.
* ============
*
* The routine computes all eigenvalues and, optionally, eigenvectors of an
* n-by-n complex Hermitian 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.
* ========================
*
* CHEEVD Example Program Results
*
* Eigenvalues
* -21.97 -0.05 6.46 16.34
*
* Eigenvectors (stored columnwise)
* ( 0.41, 0.00) ( -0.34, 0.00) ( -0.69, 0.00) ( 0.49, 0.00)
* ( 0.02, -0.30) ( 0.32, -0.21) ( -0.57, -0.22) ( -0.59, -0.21)
* ( 0.18, 0.57) ( -0.42, -0.32) ( 0.06, 0.16) ( -0.35, -0.47)
* ( -0.62, -0.09) ( -0.58, 0.35) ( -0.15, -0.31) ( -0.10, -0.12)
* =============================================================================
*
* .. Parameters ..
INTEGER N
PARAMETER ( N = 4 )
INTEGER LDA
PARAMETER ( LDA = N )
INTEGER LWMAX
PARAMETER ( LWMAX = 1000 )
*
* .. Local Scalars ..
INTEGER INFO, LWORK, LIWORK, LRWORK
*
* .. Local Arrays ..
INTEGER IWORK( LWMAX )
REAL W( N ), RWORK( LWMAX )
COMPLEX A( LDA, N ), WORK( LWMAX )
DATA A/
$ ( 3.40, 0.00),(-2.36, 1.93),(-4.68,-9.55),( 5.37, 1.23),
$ ( 0.00, 0.00),( 6.94, 0.00),( 8.13, 1.47),( 2.07, 5.78),
$ ( 0.00, 0.00),( 0.00, 0.00),(-2.14, 0.00),( 4.68,-7.44),
$ ( 0.00, 0.00),( 0.00, 0.00),( 0.00, 0.00),(-7.42, 0.00)
$ /
*
* .. External Subroutines ..
EXTERNAL CHEEVD
EXTERNAL PRINT_MATRIX, PRINT_RMATRIX
*
* .. Intrinsic Functions ..
INTRINSIC INT, MIN
*
* .. Executable Statements ..
WRITE(*,*)'CHEEVD Example Program Results'
*
* Query the optimal workspace.
*
LWORK = -1
LIWORK = -1
LRWORK = -1
CALL CHEEVD( 'Vectors', 'Lower', N, A, LDA, W, WORK, LWORK, RWORK,
$ LRWORK, IWORK, LIWORK, INFO )
LWORK = MIN( LWMAX, INT( WORK( 1 ) ) )
LRWORK = MIN( LWMAX, INT( RWORK( 1 ) ) )
LIWORK = MIN( LWMAX, IWORK( 1 ) )
*
* Solve eigenproblem.
*
CALL CHEEVD( 'Vectors', 'Lower', N, A, LDA, W, WORK, LWORK, RWORK,
$ LRWORK, 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_RMATRIX( 'Eigenvalues', 1, N, W, 1 )
*
* Print eigenvectors.
*
CALL PRINT_MATRIX( 'Eigenvectors (stored columnwise)', N, N, A,
$ LDA )
STOP
END
*
* End of CHEEVD Example.
*
* =============================================================================
*
* Auxiliary routine: printing a matrix.
*
SUBROUTINE PRINT_MATRIX( DESC, M, N, A, LDA )
CHARACTER*(*) DESC
INTEGER M, N, LDA
COMPLEX 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
*
* Auxiliary routine: printing a real matrix.
*
SUBROUTINE PRINT_RMATRIX( 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
Parent topic: CHEEVD Example