Contents
sstev - compute all eigenvalues and, optionally, eigenvec-
tors of a real symmetric tridiagonal matrix A
SUBROUTINE SSTEV(JOBZ, N, DIAG, OFFD, Z, LDZ, WORK, INFO)
CHARACTER * 1 JOBZ
INTEGER N, LDZ, INFO
REAL DIAG(*), OFFD(*), Z(LDZ,*), WORK(*)
SUBROUTINE SSTEV_64(JOBZ, N, DIAG, OFFD, Z, LDZ, WORK, INFO)
CHARACTER * 1 JOBZ
INTEGER*8 N, LDZ, INFO
REAL DIAG(*), OFFD(*), Z(LDZ,*), WORK(*)
F95 INTERFACE
SUBROUTINE STEV(JOBZ, N, DIAG, OFFD, Z, [LDZ], [WORK], [INFO])
CHARACTER(LEN=1) :: JOBZ
INTEGER :: N, LDZ, INFO
REAL, DIMENSION(:) :: DIAG, OFFD, WORK
REAL, DIMENSION(:,:) :: Z
SUBROUTINE STEV_64(JOBZ, N, DIAG, OFFD, Z, [LDZ], [WORK], [INFO])
CHARACTER(LEN=1) :: JOBZ
INTEGER(8) :: N, LDZ, INFO
REAL, DIMENSION(:) :: DIAG, OFFD, WORK
REAL, DIMENSION(:,:) :: Z
C INTERFACE
#include <sunperf.h>
void sstev(char jobz, int n, float *diag, float *offd, float
*z, int ldz, int *info);
void sstev_64(char jobz, long n, float *diag, float *offd,
float *z, long ldz, long *info);
sstev computes all eigenvalues and, optionally, eigenvectors
of a real symmetric tridiagonal matrix A.
JOBZ (input)
= 'N': Compute eigenvalues only;
= 'V': Compute eigenvalues and eigenvectors.
N (input) The order of the matrix. N >= 0.
DIAG (input/output)
On entry, the n diagonal elements of the tridiago-
nal matrix A. On exit, if INFO = 0, the eigen-
values in ascending order.
OFFD (input/output)
On entry, the (n-1) subdiagonal elements of the
tridiagonal matrix A, stored in elements 1 to N-1
of OFFD; OFFD(N) need not be set, but is used by
the routine. On exit, the contents of OFFD are
destroyed.
Z (input) 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 associ-
ated with DIAG(i). If JOBZ = 'N', then Z is not
referenced.
LDZ (input)
The leading dimension of the array Z. LDZ >= 1,
and if JOBZ = 'V', LDZ >= max(1,N).
WORK (workspace)
If JOBZ = 'N', WORK is not referenced.
INFO (output)
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille-
gal value
> 0: if INFO = i, the algorithm failed to con-
verge; i off-diagonal elements of OFFD did not
converge to zero.