Contents
sstevd - compute all eigenvalues and, optionally, eigenvec-
tors of a real symmetric tridiagonal matrix
SUBROUTINE SSTEVD(JOBZ, N, D, E, Z, LDZ, WORK, LWORK, IWORK, LIWORK,
INFO)
CHARACTER * 1 JOBZ
INTEGER N, LDZ, LWORK, LIWORK, INFO
INTEGER IWORK(*)
REAL D(*), E(*), Z(LDZ,*), WORK(*)
SUBROUTINE SSTEVD_64(JOBZ, N, D, E, Z, LDZ, WORK, LWORK, IWORK,
LIWORK, INFO)
CHARACTER * 1 JOBZ
INTEGER*8 N, LDZ, LWORK, LIWORK, INFO
INTEGER*8 IWORK(*)
REAL D(*), E(*), Z(LDZ,*), WORK(*)
F95 INTERFACE
SUBROUTINE STEVD(JOBZ, N, D, E, Z, [LDZ], [WORK], [LWORK], [IWORK],
[LIWORK], [INFO])
CHARACTER(LEN=1) :: JOBZ
INTEGER :: N, LDZ, LWORK, LIWORK, INFO
INTEGER, DIMENSION(:) :: IWORK
REAL, DIMENSION(:) :: D, E, WORK
REAL, DIMENSION(:,:) :: Z
SUBROUTINE STEVD_64(JOBZ, N, D, E, Z, [LDZ], [WORK], [LWORK], [IWORK],
[LIWORK], [INFO])
CHARACTER(LEN=1) :: JOBZ
INTEGER(8) :: N, LDZ, LWORK, LIWORK, INFO
INTEGER(8), DIMENSION(:) :: IWORK
REAL, DIMENSION(:) :: D, E, WORK
REAL, DIMENSION(:,:) :: Z
C INTERFACE
#include <sunperf.h>
void sstevd(char jobz, int n, float *d, float *e, float *z,
int ldz, int *info);
void sstevd_64(char jobz, long n, float *d, float *e, float
*z, long ldz, long *info);
sstevd computes all eigenvalues and, optionally, eigenvec-
tors of a real symmetric tridiagonal matrix. If eigenvectors
are desired, it uses a divide and conquer algorithm.
The divide and conquer algorithm makes very mild assumptions
about floating point arithmetic. It will work on machines
with a guard digit in add/subtract, or on those binary
machines without guard digits which subtract like the Cray
X-MP, Cray Y-MP, Cray C-90, or Cray-2. It could conceivably
fail on hexadecimal or decimal machines without guard
digits, but we know of none.
JOBZ (input)
= 'N': Compute eigenvalues only;
= 'V': Compute eigenvalues and eigenvectors.
N (input) The order of the matrix. N >= 0.
D (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.
E (input/output)
On entry, the (n-1) subdiagonal elements of the
tridiagonal matrix A, stored in elements 1 to N-1
of E; E(N) need not be set, but is used by the
routine. On exit, the contents of E are des-
troyed.
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 D(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)
dimension (LWORK) On exit, if INFO = 0, WORK(1)
returns the optimal LWORK.
LWORK (input)
The dimension of the array WORK. If JOBZ = 'N'
or N <= 1 then LWORK must be at least 1. If JOBZ
= 'V' and N > 1 then LWORK must be at least ( 1 +
4*N + N**2 ).
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.
IWORK (workspace/output)
On exit, if INFO = 0, IWORK(1) returns the optimal
LIWORK.
LIWORK (input)
The dimension of the array IWORK. If JOBZ = 'N'
or N <= 1 then LIWORK must be at least 1. If JOBZ
= 'V' and N > 1 then LIWORK must be at least
3+5*N.
If LIWORK = -1, then a workspace query is assumed;
the routine only calculates the optimal size of
the IWORK array, returns this value as the first
entry of the IWORK array, and no error message
related to LIWORK is issued by XERBLA.
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 E did not con-
verge to zero.