dstevd(3P) Sun Performance Library dstevd(3P)NAMEdstevd - compute all eigenvalues and, optionally, eigenvectors of a
real symmetric tridiagonal matrix
SYNOPSIS
SUBROUTINE DSTEVD(JOBZ, N, D, E, Z, LDZ, WORK, LWORK, IWORK, LIWORK,
INFO)
CHARACTER * 1 JOBZ
INTEGER N, LDZ, LWORK, LIWORK, INFO
INTEGER IWORK(*)
DOUBLE PRECISION D(*), E(*), Z(LDZ,*), WORK(*)
SUBROUTINE DSTEVD_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(*)
DOUBLE PRECISION 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(8), DIMENSION(:) :: D, E, WORK
REAL(8), 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(8), DIMENSION(:) :: D, E, WORK
REAL(8), DIMENSION(:,:) :: Z
C INTERFACE
#include <sunperf.h>
void dstevd(char jobz, int n, double *d, double *e, double *z, int ldz,
int *info);
void dstevd_64(char jobz, long n, double *d, double *e, double *z, long
ldz, long *info);
PURPOSEdstevd computes all eigenvalues and, optionally, eigenvectors 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 dig‐
its, but we know of none.
ARGUMENTS
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 tridiagonal matrix
A. On exit, if INFO = 0, the eigenvalues 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 destroyed.
Z (output)
If JOBZ = 'V', then if INFO = 0, Z contains the orthonormal
eigenvectors of the matrix A, with the i-th column of Z hold‐
ing the eigenvector associated 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 rou‐
tine 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 illegal value
> 0: if INFO = i, the algorithm failed to converge; i off-
diagonal elements of E did not converge to zero.
6 Mar 2009 dstevd(3P)
