CLAEIN uses inverse iteration to find a right or left eigenvector


 corresponding to the eigenvalue W of a complex upper Hessenberg


 matrix H.

RIGHTV

          RIGHTV is LOGICAL


          = .TRUE. : compute right eigenvector;


          = .FALSE.: compute left eigenvector.

NOINIT

          NOINIT is LOGICAL


          = .TRUE. : no initial vector supplied in V


          = .FALSE.: initial vector supplied in V.

N

          N is INTEGER


          The order of the matrix H.  N >= 0.

H

          H is COMPLEX array, dimension (LDH,N)


          The upper Hessenberg matrix H.

LDH

          LDH is INTEGER


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

W

          W is COMPLEX


          The eigenvalue of H whose corresponding right or left


          eigenvector is to be computed.

V

          V is COMPLEX array, dimension (N)


          On entry, if NOINIT = .FALSE., V must contain a starting


          vector for inverse iteration; otherwise V need not be set.


          On exit, V contains the computed eigenvector, 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|.

B

          B is COMPLEX array, dimension (LDB,N)

LDB

          LDB is INTEGER


          The leading dimension of the array B.  LDB >= max(1,N).

RWORK

          RWORK is REAL array, dimension (N)

EPS3

          EPS3 is REAL


          A small machine-dependent value which is used to perturb


          close eigenvalues, and to replace zero pivots.

SMLNUM

          SMLNUM is REAL


          A machine-dependent value close to the underflow threshold.

INFO

          INFO is INTEGER


          = 0:  successful exit


          = 1:  inverse iteration did not converge; V is set to the


                last iterate.

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

September 2012