zsteqr

NAME

zsteqr - compute all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method

SYNOPSIS

  SUBROUTINE ZSTEQR( COMPZ, N, D, E, Z, LDZ, WORK, INFO)
  CHARACTER * 1 COMPZ
  DOUBLE COMPLEX Z(LDZ,*)
  INTEGER N, LDZ, INFO
  DOUBLE PRECISION D(*), E(*), WORK(*)
 
  SUBROUTINE ZSTEQR_64( COMPZ, N, D, E, Z, LDZ, WORK, INFO)
  CHARACTER * 1 COMPZ
  DOUBLE COMPLEX Z(LDZ,*)
  INTEGER*8 N, LDZ, INFO
  DOUBLE PRECISION D(*), E(*), WORK(*)

F95 INTERFACE

  SUBROUTINE STEQR( COMPZ, [N], D, E, Z, [LDZ], [WORK], [INFO])
  CHARACTER(LEN=1) :: COMPZ
  COMPLEX(8), DIMENSION(:,:) :: Z
  INTEGER :: N, LDZ, INFO
  REAL(8), DIMENSION(:) :: D, E, WORK
 
  SUBROUTINE STEQR_64( COMPZ, [N], D, E, Z, [LDZ], [WORK], [INFO])
  CHARACTER(LEN=1) :: COMPZ
  COMPLEX(8), DIMENSION(:,:) :: Z
  INTEGER(8) :: N, LDZ, INFO
  REAL(8), DIMENSION(:) :: D, E, WORK

C INTERFACE

#include <sunperf.h>

void zsteqr(char compz, int n, double *d, double *e, doublecomplex *z, int ldz, int *info);

void zsteqr_64(char compz, long n, double *d, double *e, doublecomplex *z, long ldz, long *info);

PURPOSE

zsteqr computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method. The eigenvectors of a full or band complex Hermitian matrix can also be found if CHETRD or CHPTRD or CHBTRD has been used to reduce this matrix to tridiagonal form.

ARGUMENTS

* COMPZ (input)
* N (input): The order of the matrix. N >= 0.
* D (input/output): On entry, the diagonal elements of the tridiagonal matrix. On exit, if INFO = 0, the eigenvalues in ascending order.
* E (input/output): On entry, the (n-1) subdiagonal elements of the tridiagonal matrix. On exit, E has been destroyed.
* Z (input): On entry, if COMPZ = 'V', then Z contains the unitary matrix used in the reduction to tridiagonal form. On exit, if INFO = 0, then if COMPZ = 'V', Z contains the orthonormal eigenvectors of the original Hermitian matrix, and if COMPZ = 'I', Z contains the orthonormal eigenvectors of the symmetric tridiagonal matrix. If COMPZ = 'N', then Z is not referenced.
* LDZ (input): The leading dimension of the array Z. LDZ >= 1, and if eigenvectors are desired, then LDZ >= max(1,N).
* WORK (workspace): If COMPZ = 'N', then WORK is not referenced.
* INFO (output)