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CHEEVX Example Program in Fortran
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* =============================================================================
*
* CHEEVX Example.
* ==============
*
* Program computes eigenvalues specified by a selected range of values
* and corresponding eigenvectors of a complex Hermitian matrix A:
*
* ( 6.51, 0.00) ( -5.92, 9.53) ( -2.46, 2.91) ( 8.84, 3.21)
* ( -5.92, -9.53) ( -1.73, 0.00) ( 6.50, 2.09) ( 1.32, 8.81)
* ( -2.46, -2.91) ( 6.50, -2.09) ( 6.90, 0.00) ( -0.59, 2.47)
* ( 8.84, -3.21) ( 1.32, -8.81) ( -0.59, -2.47) ( -2.85, 0.00)
*
* Description.
* ============
*
* The routine computes selected 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.
* Eigenvalues and eigenvectors can be selected by specifying either a range
* of values or a range of indices for the desired eigenvalues.
*
* Example Program Results.
* ========================
*
* CHEEVX Example Program Results
*
* The total number of eigenvalues found: 3
*
* Selected eigenvalues
* 0.09 9.53 18.75
*
* Selected eigenvectors (stored columnwise)
* ( 0.18, 0.00) ( -0.54, 0.00) ( 0.67, 0.00)
* ( -0.40, -0.31) ( -0.21, -0.17) ( -0.30, -0.43)
* ( 0.60, 0.40) ( -0.35, -0.28) ( -0.39, -0.34)
* ( -0.34, 0.26) ( -0.57, 0.35) ( 0.05, 0.05)
* =============================================================================
*
* .. Parameters ..
INTEGER N
PARAMETER ( N = 4 )
INTEGER LDA, LDZ
PARAMETER ( LDA = N, LDZ = N )
INTEGER LWMAX
PARAMETER ( LWMAX = 1000 )
*
* .. Local Scalars ..
INTEGER INFO, LWORK, IL, IU, M
REAL ABSTOL, VL, VU
*
* .. Local Arrays ..
* IWORK dimension should be at least 5*N
INTEGER IWORK( 5*N ), IFAIL( N )
* RWORK dimension should be at least 7*N
REAL W( N ), RWORK( 7*N )
COMPLEX A( LDA, N ), Z( LDZ, N ), WORK( LWMAX )
DATA A/
$ ( 6.51, 0.00),(-5.92,-9.53),(-2.46,-2.91),( 8.84,-3.21),
$ ( 0.00, 0.00),(-1.73, 0.00),( 6.50,-2.09),( 1.32,-8.81),
$ ( 0.00, 0.00),( 0.00, 0.00),( 6.90, 0.00),(-0.59,-2.47),
$ ( 0.00, 0.00),( 0.00, 0.00),( 0.00, 0.00),(-2.85, 0.00)
$ /
*
* .. External Subroutines ..
EXTERNAL CHEEVX
EXTERNAL PRINT_MATRIX, PRINT_RMATRIX
*
* .. Intrinsic Functions ..
INTRINSIC INT, MIN
*
* .. Executable Statements ..
WRITE(*,*)'CHEEVX Example Program Results'
* Negative ABSTOL means using the default value
ABSTOL = -1.0
* Set VL, VU to compute eigenvalues in half-open (VL,VU] interval
VL = 0.0
VU = 100.0
*
* Query the optimal workspace.
*
LWORK = -1
CALL CHEEVX( 'Vectors', 'Values', 'Lower', N, A, LDA, VL, VU, IL,
$ IU, ABSTOL, M, W, Z, LDZ, WORK, LWORK, RWORK, IWORK,
$ IFAIL, INFO )
LWORK = MIN( LWMAX, INT( WORK( 1 ) ) )
*
* Solve eigenproblem.
*
CALL CHEEVX( 'Vectors', 'Values', 'Lower', N, A, LDA, VL, VU, IL,
$ IU, ABSTOL, M, W, Z, LDZ, WORK, LWORK, RWORK, IWORK,
$ IFAIL, INFO )
*
* Check for convergence.
*
IF( INFO.GT.0 ) THEN
WRITE(*,*)'The algorithm failed to compute eigenvalues.'
STOP
END IF
*
* Print the number of eigenvalues found.
*
WRITE(*,'(/A,I2)')' The total number of eigenvalues found:', M
*
* Print eigenvalues.
*
CALL PRINT_RMATRIX( 'Selected eigenvalues', 1, M, W, 1 )
*
* Print eigenvectors.
*
CALL PRINT_MATRIX( 'Selected eigenvectors (stored columnwise)',
$ N, M, Z, LDZ )
STOP
END
*
* End of CHEEVX 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: CHEEVX Example