CXML
        	    
LAPACK version 3.0
dsteqr(3)

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

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

      CHARACTER	     COMPZ

      INTEGER	     INFO, LDZ, N

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

DESCRIPTION
  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.