DSTEQR(l)								 )								 DSTEQR(l)

NAME

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

SYNOPSIS

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

	   CHARACTER	  COMPZ

	   INTEGER	  INFO, LDZ, N

	   DOUBLE	  PRECISION D( * ), E( * ), WORK( * ), Z( LDZ, * )

PURPOSE

       DSTEQR  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 symmetric matrix can also be found if DSYTRD or DSPTRD or DSBTRD 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 symmetric matrix.  On entry, Z must contain the orthogonal 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) DOUBLE PRECISION 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) DOUBLE PRECISION array, dimension (N-1)
	       On entry, the (n-1) subdiagonal elements of the tridiagonal matrix.  On exit, E has been destroyed.

       Z       (input/output) DOUBLE PRECISION array, dimension (LDZ, N)
	       On  entry, if  COMPZ = 'V', then Z contains the orthogonal 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 symmetric 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) DOUBLE PRECISION 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 orthogonally similar to the
	       original matrix.

LAPACK version 3.0						   15 June 2000 							 DSTEQR(l)