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Subroutine `[s,d]neigh` calls the ARPACK subroutine
`[s,d]laqrb` .
This routine is a modified version of the LAPACK subroutine
`[s,d]lahqr`
for computing a real Schur form for an upper Hessenberg matrix.
Subroutine `[s,d]laqrb` computes the upper quasi-triangular
Schur matrix just as `[s,d]lahqr` does
but it only computes the last components of the associated Schur vectors
since these are all that is needed for the error estimates.
The complex arithmetic subroutine `[c,z]neigh` computes
the complete Schur decomposition of the projected matrix using
LAPACK subroutine `[c,z]lahqr` .
The subroutine `[c,z]neigh` then calls the LAPACK
subroutine `[c,z]trevc`
to compute the eigenvectors of the upper triangular Schur matrix.
However, just as in real arithmetic case, only the last components of these
eigenvectors are needed for computing error estimates.

*Chao Yang*

*11/7/1997*