dsteqr man page on IRIX

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DSTEQR(3F)							    DSTEQR(3F)

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).

									Page 1

DSTEQR(3F)							    DSTEQR(3F)

     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.

									Page 2

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