From baba851215b44ac3b60b9248eb02bcce7eb76247 Mon Sep 17 00:00:00 2001 From: jason Date: Tue, 28 Oct 2008 01:38:50 +0000 Subject: Move LAPACK trunk into position. --- SRC/sstev.f | 163 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 163 insertions(+) create mode 100644 SRC/sstev.f (limited to 'SRC/sstev.f') diff --git a/SRC/sstev.f b/SRC/sstev.f new file mode 100644 index 00000000..fabd6e77 --- /dev/null +++ b/SRC/sstev.f @@ -0,0 +1,163 @@ + SUBROUTINE SSTEV( JOBZ, N, D, E, Z, LDZ, WORK, INFO ) +* +* -- LAPACK driver routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + CHARACTER JOBZ + INTEGER INFO, LDZ, N +* .. +* .. Array Arguments .. + REAL D( * ), E( * ), WORK( * ), Z( LDZ, * ) +* .. +* +* Purpose +* ======= +* +* SSTEV computes all eigenvalues and, optionally, eigenvectors of a +* real symmetric tridiagonal matrix A. +* +* Arguments +* ========= +* +* JOBZ (input) CHARACTER*1 +* = 'N': Compute eigenvalues only; +* = 'V': Compute eigenvalues and eigenvectors. +* +* N (input) INTEGER +* The order of the matrix. N >= 0. +* +* D (input/output) REAL array, dimension (N) +* On entry, the n diagonal elements of the tridiagonal matrix +* A. +* On exit, if INFO = 0, the eigenvalues in ascending order. +* +* E (input/output) REAL array, dimension (N-1) +* On entry, the (n-1) subdiagonal elements of the tridiagonal +* matrix A, stored in elements 1 to N-1 of E. +* On exit, the contents of E are destroyed. +* +* Z (output) REAL array, dimension (LDZ, N) +* If JOBZ = 'V', then if INFO = 0, Z contains the orthonormal +* eigenvectors of the matrix A, with the i-th column of Z +* holding the eigenvector associated with D(i). +* If JOBZ = 'N', then Z is not referenced. +* +* LDZ (input) INTEGER +* The leading dimension of the array Z. LDZ >= 1, and if +* JOBZ = 'V', LDZ >= max(1,N). +* +* WORK (workspace) REAL array, dimension (max(1,2*N-2)) +* If JOBZ = 'N', WORK is not referenced. +* +* 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 E did not converge to zero. +* +* ===================================================================== +* +* .. Parameters .. + REAL ZERO, ONE + PARAMETER ( ZERO = 0.0E0, ONE = 1.0E0 ) +* .. +* .. Local Scalars .. + LOGICAL WANTZ + INTEGER IMAX, ISCALE + REAL BIGNUM, EPS, RMAX, RMIN, SAFMIN, SIGMA, SMLNUM, + $ TNRM +* .. +* .. External Functions .. + LOGICAL LSAME + REAL SLAMCH, SLANST + EXTERNAL LSAME, SLAMCH, SLANST +* .. +* .. External Subroutines .. + EXTERNAL SSCAL, SSTEQR, SSTERF, XERBLA +* .. +* .. Intrinsic Functions .. + INTRINSIC SQRT +* .. +* .. Executable Statements .. +* +* Test the input parameters. +* + WANTZ = LSAME( JOBZ, 'V' ) +* + INFO = 0 + IF( .NOT.( WANTZ .OR. LSAME( JOBZ, 'N' ) ) ) THEN + INFO = -1 + ELSE IF( N.LT.0 ) THEN + INFO = -2 + ELSE IF( LDZ.LT.1 .OR. ( WANTZ .AND. LDZ.LT.N ) ) THEN + INFO = -6 + END IF +* + IF( INFO.NE.0 ) THEN + CALL XERBLA( 'SSTEV ', -INFO ) + RETURN + END IF +* +* Quick return if possible +* + IF( N.EQ.0 ) + $ RETURN +* + IF( N.EQ.1 ) THEN + IF( WANTZ ) + $ Z( 1, 1 ) = ONE + RETURN + END IF +* +* Get machine constants. +* + SAFMIN = SLAMCH( 'Safe minimum' ) + EPS = SLAMCH( 'Precision' ) + SMLNUM = SAFMIN / EPS + BIGNUM = ONE / SMLNUM + RMIN = SQRT( SMLNUM ) + RMAX = SQRT( BIGNUM ) +* +* Scale matrix to allowable range, if necessary. +* + ISCALE = 0 + TNRM = SLANST( 'M', N, D, E ) + IF( TNRM.GT.ZERO .AND. TNRM.LT.RMIN ) THEN + ISCALE = 1 + SIGMA = RMIN / TNRM + ELSE IF( TNRM.GT.RMAX ) THEN + ISCALE = 1 + SIGMA = RMAX / TNRM + END IF + IF( ISCALE.EQ.1 ) THEN + CALL SSCAL( N, SIGMA, D, 1 ) + CALL SSCAL( N-1, SIGMA, E( 1 ), 1 ) + END IF +* +* For eigenvalues only, call SSTERF. For eigenvalues and +* eigenvectors, call SSTEQR. +* + IF( .NOT.WANTZ ) THEN + CALL SSTERF( N, D, E, INFO ) + ELSE + CALL SSTEQR( 'I', N, D, E, Z, LDZ, WORK, 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 SSCAL( IMAX, ONE / SIGMA, D, 1 ) + END IF +* + RETURN +* +* End of SSTEV +* + END -- cgit v1.2.3