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Diffstat (limited to 'SRC/dsyev.f')
| -rw-r--r-- | SRC/dsyev.f | 211 |
1 files changed, 211 insertions, 0 deletions
diff --git a/SRC/dsyev.f b/SRC/dsyev.f new file mode 100644 index 00000000..d73600a2 --- /dev/null +++ b/SRC/dsyev.f @@ -0,0 +1,211 @@ + SUBROUTINE DSYEV( JOBZ, UPLO, N, A, LDA, W, WORK, LWORK, INFO ) +* +* -- LAPACK driver routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + CHARACTER JOBZ, UPLO + INTEGER INFO, LDA, LWORK, N +* .. +* .. Array Arguments .. + DOUBLE PRECISION A( LDA, * ), W( * ), WORK( * ) +* .. +* +* Purpose +* ======= +* +* DSYEV computes all eigenvalues and, optionally, eigenvectors of a +* real symmetric matrix A. +* +* Arguments +* ========= +* +* JOBZ (input) CHARACTER*1 +* = 'N': Compute eigenvalues only; +* = 'V': Compute eigenvalues and eigenvectors. +* +* UPLO (input) CHARACTER*1 +* = 'U': Upper triangle of A is stored; +* = 'L': Lower triangle of A is stored. +* +* N (input) INTEGER +* The order of the matrix A. N >= 0. +* +* A (input/output) DOUBLE PRECISION array, dimension (LDA, N) +* On entry, the symmetric matrix A. If UPLO = 'U', the +* leading N-by-N upper triangular part of A contains the +* upper triangular part of the matrix A. If UPLO = 'L', +* the leading N-by-N lower triangular part of A contains +* the lower triangular part of the matrix A. +* On exit, if JOBZ = 'V', then if INFO = 0, A contains the +* orthonormal eigenvectors of the matrix A. +* If JOBZ = 'N', then on exit the lower triangle (if UPLO='L') +* or the upper triangle (if UPLO='U') of A, including the +* diagonal, is destroyed. +* +* LDA (input) INTEGER +* The leading dimension of the array A. LDA >= max(1,N). +* +* W (output) DOUBLE PRECISION array, dimension (N) +* If INFO = 0, the eigenvalues in ascending order. +* +* WORK (workspace/output) DOUBLE PRECISION array, dimension (MAX(1,LWORK)) +* On exit, if INFO = 0, WORK(1) returns the optimal LWORK. +* +* LWORK (input) INTEGER +* The length of the array WORK. LWORK >= max(1,3*N-1). +* For optimal efficiency, LWORK >= (NB+2)*N, +* where NB is the blocksize for DSYTRD returned by ILAENV. +* +* If LWORK = -1, then a workspace query is assumed; the routine +* only calculates the optimal size of the WORK array, returns +* this value as the first entry of the WORK array, and no error +* message related to LWORK is issued by XERBLA. +* +* INFO (output) INTEGER +* = 0: successful exit +* < 0: if INFO = -i, the i-th argument had an illegal value +* > 0: if INFO = i, the algorithm failed to converge; i +* off-diagonal elements of an intermediate tridiagonal +* form did not converge to zero. +* +* ===================================================================== +* +* .. Parameters .. + DOUBLE PRECISION ZERO, ONE + PARAMETER ( ZERO = 0.0D0, ONE = 1.0D0 ) +* .. +* .. Local Scalars .. + LOGICAL LOWER, LQUERY, WANTZ + INTEGER IINFO, IMAX, INDE, INDTAU, INDWRK, ISCALE, + $ LLWORK, LWKOPT, NB + DOUBLE PRECISION ANRM, BIGNUM, EPS, RMAX, RMIN, SAFMIN, SIGMA, + $ SMLNUM +* .. +* .. External Functions .. + LOGICAL LSAME + INTEGER ILAENV + DOUBLE PRECISION DLAMCH, DLANSY + EXTERNAL LSAME, ILAENV, DLAMCH, DLANSY +* .. +* .. External Subroutines .. + EXTERNAL DLASCL, DORGTR, DSCAL, DSTEQR, DSTERF, DSYTRD, + $ XERBLA +* .. +* .. Intrinsic Functions .. + INTRINSIC MAX, SQRT +* .. +* .. Executable Statements .. +* +* Test the input parameters. +* + WANTZ = LSAME( JOBZ, 'V' ) + LOWER = LSAME( UPLO, 'L' ) + LQUERY = ( LWORK.EQ.-1 ) +* + INFO = 0 + IF( .NOT.( WANTZ .OR. LSAME( JOBZ, 'N' ) ) ) THEN + INFO = -1 + ELSE IF( .NOT.( LOWER .OR. LSAME( UPLO, 'U' ) ) ) THEN + INFO = -2 + ELSE IF( N.LT.0 ) THEN + INFO = -3 + ELSE IF( LDA.LT.MAX( 1, N ) ) THEN + INFO = -5 + END IF +* + IF( INFO.EQ.0 ) THEN + NB = ILAENV( 1, 'DSYTRD', UPLO, N, -1, -1, -1 ) + LWKOPT = MAX( 1, ( NB+2 )*N ) + WORK( 1 ) = LWKOPT +* + IF( LWORK.LT.MAX( 1, 3*N-1 ) .AND. .NOT.LQUERY ) + $ INFO = -8 + END IF +* + IF( INFO.NE.0 ) THEN + CALL XERBLA( 'DSYEV ', -INFO ) + RETURN + ELSE IF( LQUERY ) THEN + RETURN + END IF +* +* Quick return if possible +* + IF( N.EQ.0 ) THEN + RETURN + END IF +* + IF( N.EQ.1 ) THEN + W( 1 ) = A( 1, 1 ) + WORK( 1 ) = 2 + IF( WANTZ ) + $ A( 1, 1 ) = ONE + RETURN + END IF +* +* Get machine constants. +* + SAFMIN = DLAMCH( 'Safe minimum' ) + EPS = DLAMCH( 'Precision' ) + SMLNUM = SAFMIN / EPS + BIGNUM = ONE / SMLNUM + RMIN = SQRT( SMLNUM ) + RMAX = SQRT( BIGNUM ) +* +* Scale matrix to allowable range, if necessary. +* + ANRM = DLANSY( 'M', UPLO, N, A, LDA, WORK ) + ISCALE = 0 + IF( ANRM.GT.ZERO .AND. ANRM.LT.RMIN ) THEN + ISCALE = 1 + SIGMA = RMIN / ANRM + ELSE IF( ANRM.GT.RMAX ) THEN + ISCALE = 1 + SIGMA = RMAX / ANRM + END IF + IF( ISCALE.EQ.1 ) + $ CALL DLASCL( UPLO, 0, 0, ONE, SIGMA, N, N, A, LDA, INFO ) +* +* Call DSYTRD to reduce symmetric matrix to tridiagonal form. +* + INDE = 1 + INDTAU = INDE + N + INDWRK = INDTAU + N + LLWORK = LWORK - INDWRK + 1 + CALL DSYTRD( UPLO, N, A, LDA, W, WORK( INDE ), WORK( INDTAU ), + $ WORK( INDWRK ), LLWORK, IINFO ) +* +* For eigenvalues only, call DSTERF. For eigenvectors, first call +* DORGTR to generate the orthogonal matrix, then call DSTEQR. +* + IF( .NOT.WANTZ ) THEN + CALL DSTERF( N, W, WORK( INDE ), INFO ) + ELSE + CALL DORGTR( UPLO, N, A, LDA, WORK( INDTAU ), WORK( INDWRK ), + $ LLWORK, IINFO ) + CALL DSTEQR( JOBZ, N, W, WORK( INDE ), A, LDA, WORK( INDTAU ), + $ INFO ) + END IF +* +* If matrix was scaled, then rescale eigenvalues appropriately. +* + IF( ISCALE.EQ.1 ) THEN + IF( INFO.EQ.0 ) THEN + IMAX = N + ELSE + IMAX = INFO - 1 + END IF + CALL DSCAL( IMAX, ONE / SIGMA, W, 1 ) + END IF +* +* Set WORK(1) to optimal workspace size. +* + WORK( 1 ) = LWKOPT +* + RETURN +* +* End of DSYEV +* + END |