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 eigenvalue), 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 2.0  —  08 October 1994