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CHEEVR Example Program in Fortran
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* =============================================================================
*
* CHEEVR Example.
* ==============
*
* Program computes eigenvalues specified by a selected range of values
* and corresponding eigenvectors of a complex Hermitian matrix A using the
* Relatively Robust Representations, where A is:
*
* ( -2.16, 0.00) ( -0.16, -4.86) ( -7.23, -9.38) ( -0.04, 6.86)
* ( -0.16, 4.86) ( 7.45, 0.00) ( 4.39, 6.29) ( -8.11, -4.41)
* ( -7.23, 9.38) ( 4.39, -6.29) ( -9.03, 0.00) ( -6.89, -7.66)
* ( -0.04, -6.86) ( -8.11, 4.41) ( -6.89, 7.66) ( 7.76, 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.
* ========================
*
* CHEEVR Example Program Results
*
* The total number of eigenvalues found: 2
*
* Selected eigenvalues
* -4.18 3.57
*
* Selected eigenvectors (stored columnwise)
* ( 0.68, 0.00) ( 0.38, 0.00)
* ( 0.03, 0.18) ( 0.54, -0.57)
* ( -0.03, 0.21) ( -0.40, 0.04)
* ( 0.20, 0.64) ( -0.14, -0.26)
* =============================================================================
*
* .. Parameters ..
INTEGER N
PARAMETER ( N = 4 )
INTEGER LDA, LDZ
PARAMETER ( LDA = N, LDZ = N )
INTEGER LWMAX
PARAMETER ( LWMAX = 1000 )
*
* .. Local Scalars ..
INTEGER INFO, LWORK, LRWORK, LIWORK, IL, IU, M
REAL ABSTOL, VL, VU
*
* .. Local Arrays ..
INTEGER ISUPPZ( N ), IWORK( LWMAX )
REAL W( N ), RWORK( LWMAX )
COMPLEX A( LDA, N ), Z( LDZ, N ), WORK( LWMAX )
DATA A/
$ (-2.16, 0.00),(-0.16, 4.86),(-7.23, 9.38),(-0.04,-6.86),
$ ( 0.00, 0.00),( 7.45, 0.00),( 4.39,-6.29),(-8.11, 4.41),
$ ( 0.00, 0.00),( 0.00, 0.00),(-9.03, 0.00),(-6.89, 7.66),
$ ( 0.00, 0.00),( 0.00, 0.00),( 0.00, 0.00),( 7.76, 0.00)
$ /
*
* .. External Subroutines ..
EXTERNAL CHEEVR
EXTERNAL PRINT_MATRIX, PRINT_RMATRIX
*
* .. Intrinsic Functions ..
INTRINSIC INT, MIN
*
* .. Executable Statements ..
WRITE(*,*)'CHEEVR 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 = -5.0
VU = 5.0
*
* Query the optimal workspace.
*
LWORK = -1
LRWORK = -1
LIWORK = -1
CALL CHEEVR( 'Vectors', 'Values', 'Lower', N, A, LDA, VL, VU, IL,
$ IU, ABSTOL, M, W, Z, LDZ, ISUPPZ, 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 CHEEVR( 'Vectors', 'Values', 'Lower', N, A, LDA, VL, VU, IL,
$ IU, ABSTOL, M, W, Z, LDZ, ISUPPZ, 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 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 CHEEVR 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: CHEEVR Example