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CSTEQR(l)					)					CSTEQR(l)

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

SYNOPSIS
       SUBROUTINE CSTEQR( COMPZ, N, D, E, Z, LDZ, WORK, INFO )

	   CHARACTER	  COMPZ

	   INTEGER	  INFO, LDZ, N

	   REAL 	  D( * ), E( * ), WORK( * )

	   COMPLEX	  Z( LDZ, * )

PURPOSE
       CSTEQR 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 Her-
       mitian matrix can also be found if CHETRD or CHPTRD or CHBTRD has been used to reduce this
       matrix to tridiagonal form.

ARGUMENTS
       COMPZ   (input) CHARACTER*1
	       = 'N':  Compute eigenvalues only.
	       = 'V':  Compute eigenvalues and eigenvectors of the original Hermitian matrix.  On
	       entry, Z must contain the unitary matrix used to reduce	the  original  matrix  to
	       tridiagonal form.  = 'I':  Compute eigenvalues and eigenvectors of the tridiagonal
	       matrix.	Z is initialized to the identity matrix.

       N       (input) INTEGER
	       The order of the matrix.  N >= 0.

       D       (input/output) REAL array, dimension (N)
	       On entry, the diagonal elements of the tridiagonal matrix.  On exit, if INFO =  0,
	       the eigenvalues in ascending order.

       E       (input/output) REAL array, dimension (N-1)
	       On  entry,  the	(n-1) subdiagonal elements of the tridiagonal matrix.  On exit, E
	       has been destroyed.

       Z       (input/output) COMPLEX array, dimension (LDZ, N)
	       On entry, if  COMPZ = 'V', then Z contains the unitary matrix used in  the  reduc-
	       tion  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) INTEGER
	       The leading dimension of the array Z.  LDZ >= 1, and if eigenvectors are  desired,
	       then  LDZ >= max(1,N).

       WORK    (workspace) REAL array, dimension (max(1,2*N-2))
	       If COMPZ = 'N', then WORK is not referenced.

       INFO    (output) INTEGER
	       = 0:  successful exit
	       < 0:  if INFO = -i, the i-th argument had an illegal value
	       >  0:   the  algorithm  has  failed to find all the eigenvalues in a total of 30*N
	       iterations; if INFO = i, then i elements of E have not converged to zero; on exit,
	       D  and E contain the elements of a symmetric tridiagonal matrix which is unitarily
	       similar to the original matrix.

LAPACK version 3.0			   15 June 2000 				CSTEQR(l)
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