dlasorte(3) [debian man page]

DLASORTE(l)						   LAPACK routine (version 1.5) 					       DLASORTE(l)

NAME

       DLASORTE - sort eigenpairs so that real eigenpairs are together and  complex are together

SYNOPSIS

       SUBROUTINE DLASORTE ( S, LDS, J, OUT, INFO )

	   INTEGER	   INFO, J, LDS

	   DOUBLE	   PRECISION OUT( J, * ), S( LDS, * )

PURPOSE

       DLASORTE sorts eigenpairs so that real eigenpairs are together and
	 complex are together.	This way one can employ 2x2 shifts easily
	 since every 2nd subdiagonal is guaranteed to be zero.
       This routine does no parallel work and makes no calls.

ARGUMENTS

       S       (local input/output) DOUBLE PRECISION array, dimension LDS
	       On  entry,  a  matrix  already  in Schur form.  On exit, the diagonal blocks of S have been rewritten to pair the eigenvalues.  The
	       resulting matrix is no longer similar to the input.

       LDS     (local input) INTEGER
	       On entry, the leading dimension of the local array S.  Unchanged on exit.

       J       (local input) INTEGER
	       On entry, the order of the matrix S.  Unchanged on exit.

       OUT     (local input/output) DOUBLE PRECISION array, dimension Jx2
	       This is the work buffer required by this routine.

       INFO    (local input) INTEGER
	       This is set if the input matrix had an odd number of real eigenvalues and things couldn't be paired or if the input  matrix  S  was
	       not originally in Schur form.  0 indicates successful completion.

	       Implemented by:	G. Henry, May 1, 1997

LAPACK version 1.5						    12 May 1997 						       DLASORTE(l)

DSTEQR2(l)						   LAPACK routine (version 2.0) 						DSTEQR2(l)

NAME

       DSTEQR2 - i a modified version of LAPACK routine DSTEQR

SYNOPSIS

       SUBROUTINE DSTEQR2( COMPZ, N, D, E, Z, LDZ, NR, WORK, INFO )

	   CHARACTER	   COMPZ

	   INTEGER	   INFO, LDZ, N, NR

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

PURPOSE

       DSTEQR2	is  a  modified  version  of LAPACK routine DSTEQR.  DSTEQR2 computes all eigenvalues and, optionally, eigenvectors of a symmetric
       tridiagonal matrix using the implicit QL or QR method.  DSTEQR2 is modified from DSTEQR to allow each ScaLAPACK process running DSTEQR2	to
       perform updates on a distributed matrix Q.  Proper usage of DSTEQR2 can be gleaned from examination of ScaLAPACK's PDSYEV.

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) 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       (local input/local output) DOUBLE PRECISION 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) 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.

modified LAPACK routine 					    12 May 1997 							DSTEQR2(l)