SRC/ztgevc.f(3)            Library Functions Manual            SRC/ztgevc.f(3)

NAME
       SRC/ztgevc.f

SYNOPSIS
   Functions/Subroutines
       subroutine ztgevc (side, howmny, select, n, s, lds, p, ldp, vl, ldvl,
           vr, ldvr, mm, m, work, rwork, info)
           ZTGEVC

Function/Subroutine Documentation
   subroutine ztgevc (character side, character howmny, logical, dimension( *
       ) select, integer n, complex*16, dimension( lds, * ) s, integer lds,
       complex*16, dimension( ldp, * ) p, integer ldp, complex*16, dimension(
       ldvl, * ) vl, integer ldvl, complex*16, dimension( ldvr, * ) vr,
       integer ldvr, integer mm, integer m, complex*16, dimension( * ) work,
       double precision, dimension( * ) rwork, integer info)
       ZTGEVC

       Purpose:


            ZTGEVC computes some or all of the right and/or left eigenvectors of
            a pair of complex matrices (S,P), where S and P are upper triangular.
            Matrix pairs of this type are produced by the generalized Schur
            factorization of a complex matrix pair (A,B):

               A = Q*S*Z**H,  B = Q*P*Z**H

            as computed by ZGGHRD + ZHGEQZ.

            The right eigenvector x and the left eigenvector y of (S,P)
            corresponding to an eigenvalue w are defined by:

               S*x = w*P*x,  (y**H)*S = w*(y**H)*P,

            where y**H denotes the conjugate transpose of y.
            The eigenvalues are not input to this routine, but are computed
            directly from the diagonal elements of S and P.

            This routine returns the matrices X and/or Y of right and left
            eigenvectors of (S,P), or the products Z*X and/or Q*Y,
            where Z and Q are input matrices.
            If Q and Z are the unitary factors from the generalized Schur
            factorization of a matrix pair (A,B), then Z*X and Q*Y
            are the matrices of right and left eigenvectors of (A,B).

       Parameters
           SIDE

                     SIDE is CHARACTER*1
                     = 'R': compute right eigenvectors only;
                     = 'L': compute left eigenvectors only;
                     = 'B': compute both right and left eigenvectors.

           HOWMNY

                     HOWMNY is CHARACTER*1
                     = 'A': compute all right and/or left eigenvectors;
                     = 'B': compute all right and/or left eigenvectors,
                            backtransformed by the matrices in VR and/or VL;
                     = 'S': compute selected right and/or left eigenvectors,
                            specified by the logical array SELECT.

           SELECT

                     SELECT is LOGICAL array, dimension (N)
                     If HOWMNY='S', SELECT specifies the eigenvectors to be
                     computed.  The eigenvector corresponding to the j-th
                     eigenvalue is computed if SELECT(j) = .TRUE..
                     Not referenced if HOWMNY = 'A' or 'B'.

           N

                     N is INTEGER
                     The order of the matrices S and P.  N >= 0.

           S

                     S is COMPLEX*16 array, dimension (LDS,N)
                     The upper triangular matrix S from a generalized Schur
                     factorization, as computed by ZHGEQZ.

           LDS

                     LDS is INTEGER
                     The leading dimension of array S.  LDS >= max(1,N).

           P

                     P is COMPLEX*16 array, dimension (LDP,N)
                     The upper triangular matrix P from a generalized Schur
                     factorization, as computed by ZHGEQZ.  P must have real
                     diagonal elements.

           LDP

                     LDP is INTEGER
                     The leading dimension of array P.  LDP >= max(1,N).

           VL

                     VL is COMPLEX*16 array, dimension (LDVL,MM)
                     On entry, if SIDE = 'L' or 'B' and HOWMNY = 'B', VL must
                     contain an N-by-N matrix Q (usually the unitary matrix Q
                     of left Schur vectors returned by ZHGEQZ).
                     On exit, if SIDE = 'L' or 'B', VL contains:
                     if HOWMNY = 'A', the matrix Y of left eigenvectors of (S,P);
                     if HOWMNY = 'B', the matrix Q*Y;
                     if HOWMNY = 'S', the left eigenvectors of (S,P) specified by
                                 SELECT, stored consecutively in the columns of
                                 VL, in the same order as their eigenvalues.
                     Not referenced if SIDE = 'R'.

           LDVL

                     LDVL is INTEGER
                     The leading dimension of array VL.  LDVL >= 1, and if
                     SIDE = 'L' or 'l' or 'B' or 'b', LDVL >= N.

           VR

                     VR is COMPLEX*16 array, dimension (LDVR,MM)
                     On entry, if SIDE = 'R' or 'B' and HOWMNY = 'B', VR must
                     contain an N-by-N matrix Z (usually the unitary matrix Z
                     of right Schur vectors returned by ZHGEQZ).
                     On exit, if SIDE = 'R' or 'B', VR contains:
                     if HOWMNY = 'A', the matrix X of right eigenvectors of (S,P);
                     if HOWMNY = 'B', the matrix Z*X;
                     if HOWMNY = 'S', the right eigenvectors of (S,P) specified by
                                 SELECT, stored consecutively in the columns of
                                 VR, in the same order as their eigenvalues.
                     Not referenced if SIDE = 'L'.

           LDVR

                     LDVR is INTEGER
                     The leading dimension of the array VR.  LDVR >= 1, and if
                     SIDE = 'R' or 'B', LDVR >= N.

           MM

                     MM is INTEGER
                     The number of columns in the arrays VL and/or VR. MM >= M.

           M

                     M is INTEGER
                     The number of columns in the arrays VL and/or VR actually
                     used to store the eigenvectors.  If HOWMNY = 'A' or 'B', M
                     is set to N.  Each selected eigenvector occupies one column.

           WORK

                     WORK is COMPLEX*16 array, dimension (2*N)

           RWORK

                     RWORK is DOUBLE PRECISION array, dimension (2*N)

           INFO

                     INFO is INTEGER
                     = 0:  successful exit.
                     < 0:  if INFO = -i, the i-th argument had an illegal value.

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Definition at line 217 of file ztgevc.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

LAPACK                          Version 3.12.0                 SRC/ztgevc.f(3)