ssteqr2(3) [debian man page]

SSTEQR2(l)						   LAPACK routine (version 2.0) 						SSTEQR2(l)

NAME

       SSTEQR2 - i a modified version of LAPACK routine SSTEQR

SYNOPSIS

       SUBROUTINE SSTEQR2( COMPZ, N, D, E, Z, LDZ, NR, WORK, INFO )

	   CHARACTER	   COMPZ

	   INTEGER	   INFO, LDZ, N, NR

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

PURPOSE

       SSTEQR2	is  a  modified  version  of LAPACK routine SSTEQR.  SSTEQR2 computes all eigenvalues and, optionally, eigenvectors of a symmetric
       tridiagonal matrix using the implicit QL or QR method.  running SSTEQR2 to perform updates on a distributed  matrix  Q.	 Proper  usage	of
       SSTEQR2 can be gleaned from examination of ScaLAPACK's PSSYEV.

ARGUMENTS

       COMPZ   (input) CHARACTER*1
	       = 'N':  Compute eigenvalues only.
	       = 'I':  Compute eigenvalues and eigenvectors of the tridiagonal matrix.	Z must be initialized to the identity matrix by PDLASET or
	       DLASET prior to entering this subroutine.

       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       (local input/local output) REAL array, global
	       dimension (N, N), local dimension (LDZ, NR).  On entry, if  COMPZ = 'V', then Z contains the orthogonal 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 sym-
	       metric 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).

       NR      (input) INTEGER
	       NR = MAX(1, NUMROC( N, NB, MYPROW, 0, NPROCS ) ).  If COMPZ = 'N', then NR is not referenced.

       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 orthogonally similar to the
	       original matrix.

modified LAPACK routine 					    12 May 1997 							SSTEQR2(l)

ssteqr.f(3)							      LAPACK							       ssteqr.f(3)

NAME

       ssteqr.f -

SYNOPSIS

   Functions/Subroutines
       subroutine ssteqr (COMPZ, N, D, E, Z, LDZ, WORK, INFO)
	   SSTEQR

Function/Subroutine Documentation
   subroutine ssteqr (characterCOMPZ, integerN, real, dimension( * )D, real, dimension( * )E, real, dimension( ldz, * )Z, integerLDZ, real,
       dimension( * )WORK, integerINFO)
       SSTEQR

       Purpose:

	    SSTEQR 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 SSYTRD or SSPTRD or SSBTRD has been used to reduce this matrix to
	    tridiagonal form.

       Parameters:
	   COMPZ

		     COMPZ is 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

		     N is INTEGER
		     The order of the matrix.  N >= 0.

	   D

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

	   E

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

	   Z

		     Z is REAL 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

		     LDZ is INTEGER
		     The leading dimension of the array Z.  LDZ >= 1, and if
		     eigenvectors are desired, then  LDZ >= max(1,N).

	   WORK

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

	   INFO

		     INFO is 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.

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   November 2011

       Definition at line 132 of file ssteqr.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2							  Tue Sep 25 2012						       ssteqr.f(3)