redhat man page for dlaein

DLAEIN(l)								 )								 DLAEIN(l)

NAME
       DLAEIN  -  use  inverse	iteration  to  find a right or left eigenvector corresponding to the eigenvalue (WR,WI) of a real upper Hessenberg
       matrix H

SYNOPSIS
       SUBROUTINE DLAEIN( RIGHTV, NOINIT, N, H, LDH, WR, WI, VR, VI, B, LDB, WORK, EPS3, SMLNUM, BIGNUM, INFO )

	   LOGICAL	  NOINIT, RIGHTV

	   INTEGER	  INFO, LDB, LDH, N

	   DOUBLE	  PRECISION BIGNUM, EPS3, SMLNUM, WI, WR

	   DOUBLE	  PRECISION B( LDB, * ), H( LDH, * ), VI( * ), VR( * ), WORK( * )

PURPOSE
       DLAEIN uses inverse iteration to find a right or left eigenvector corresponding to the eigenvalue (WR,WI) of a real upper Hessenberg matrix
       H.

ARGUMENTS
       RIGHTV	(input) LOGICAL
		= .TRUE. : compute right eigenvector;
		= .FALSE.: compute left eigenvector.

       NOINIT	(input) LOGICAL
		= .TRUE. : no initial vector supplied in (VR,VI).
		= .FALSE.: initial vector supplied in (VR,VI).

       N       (input) INTEGER
	       The order of the matrix H.  N >= 0.

       H       (input) DOUBLE PRECISION array, dimension (LDH,N)
	       The upper Hessenberg matrix H.

       LDH     (input) INTEGER
	       The leading dimension of the array H.  LDH >= max(1,N).

       WR      (input) DOUBLE PRECISION
	       WI	(input) DOUBLE PRECISION The real and imaginary parts of the eigenvalue of H whose corresponding right or left eigenvector
	       is to be computed.

       VR      (input/output) DOUBLE PRECISION array, dimension (N)
	       VI      (input/output) DOUBLE PRECISION array, dimension (N) On entry, if NOINIT = .FALSE. and WI = 0.0, VR  must  contain  a  real
	       starting  vector  for inverse iteration using the real eigenvalue WR; if NOINIT = .FALSE. and WI.ne.0.0, VR and VI must contain the
	       real and imaginary parts of a complex starting vector for inverse iteration using the complex eigenvalue (WR,WI); otherwise VR  and
	       VI  need  not be set.  On exit, if WI = 0.0 (real eigenvalue), VR contains the computed real eigenvector; if WI.ne.0.0 (complex ei-
	       genvalue), VR and VI contain the real and imaginary parts of the computed complex eigenvector. The  eigenvector	is  normalized	so
	       that the component of largest magnitude has magnitude 1; here the magnitude of a complex number (x,y) is taken to be |x| + |y|.	VI
	       is not referenced if WI = 0.0.

       B       (workspace) DOUBLE PRECISION array, dimension (LDB,N)

       LDB     (input) INTEGER
	       The leading dimension of the array B.  LDB >= N+1.

       WORK   (workspace) DOUBLE PRECISION array, dimension (N)

       EPS3    (input) DOUBLE PRECISION
	       A small machine-dependent value which is used to perturb close eigenvalues, and to replace zero pivots.

       SMLNUM  (input) DOUBLE PRECISION
	       A machine-dependent value close to the underflow threshold.

       BIGNUM  (input) DOUBLE PRECISION
	       A machine-dependent value close to the overflow threshold.

       INFO    (output) INTEGER
	       = 0:  successful exit
	       = 1:  inverse iteration did not converge; VR is set to the last iterate, and so is VI if WI.ne.0.0.

LAPACK version 3.0						   15 June 2000 							 DLAEIN(l)