DSTEQR(l)		LAPACK routine (version	1.1)		    DSTEQR(l)

NAME
  DSTEQR - compute all eigenvalues and,	optionally, eigenvectors of a sym-
  metric 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 sym-
  metric tridiagonal matrix using the implicit QL or QR	method.	 The eigen-
  vectors 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 sym-
	  metric 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	ini-
	  tialized 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  COMPZ =
	  'V', Z contains the orthonormal eigenvectors of the original sym-
	  metric matrix, and if	COMPZ =	'I', Z contains	the orthonormal
	  eigenvectors of the symmetric	tridiagonal matrix.  If	an error exit
	  is made, Z contains the eigenvectors associated with the stored
	  eigenvalues.	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.