• NAME
• SYNOPSIS
• F95 INTERFACE
• C INTERFACE
• PURPOSE
• ARGUMENTS

NAME

dstev - compute all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix A

SYNOPSIS

  SUBROUTINE DSTEV( JOBZ, N, DIAG, OFFD, Z, LDZ, WORK, INFO)
  CHARACTER * 1 JOBZ
  INTEGER N, LDZ, INFO
  DOUBLE PRECISION DIAG(*), OFFD(*), Z(LDZ,*), WORK(*)

  SUBROUTINE DSTEV_64( JOBZ, N, DIAG, OFFD, Z, LDZ, WORK, INFO)
  CHARACTER * 1 JOBZ
  INTEGER*8 N, LDZ, INFO
  DOUBLE PRECISION 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(8), DIMENSION(:) :: DIAG, OFFD, WORK
  REAL(8), DIMENSION(:,:) :: Z

  SUBROUTINE STEV_64( JOBZ, [N], DIAG, OFFD, Z, [LDZ], [WORK], [INFO])
  CHARACTER(LEN=1) :: JOBZ
  INTEGER(8) :: N, LDZ, INFO
  REAL(8), DIMENSION(:) :: DIAG, OFFD, WORK
  REAL(8), DIMENSION(:,:) :: Z

C INTERFACE

#include <sunperf.h>

void dstev(char jobz, int n, double *diag, double *offd, double *z, int ldz, int *info);

void dstev_64(char jobz, long n, double *diag, double *offd, double *z, long ldz, long *info);

PURPOSE

dstev computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix A.

ARGUMENTS

• 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 tridiagonal matrix A. On exit, if INFO = 0, the eigenvalues 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 (output)
  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 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 illegal value

   > 0:  if INFO  = i, the algorithm failed to converge; i
  off-diagonal elements of OFFD did not converge to zero.