NAME

       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 (characterSIDE, characterHOWMNY, logical, dimension( * )SELECT, integerN,
       complex*16, dimension( lds, * )S, integerLDS, complex*16, dimension( ldp, * )P,
       integerLDP, complex*16, dimension( ldvl, * )VL, integerLDVL, complex*16, dimension( ldvr,
       * )VR, integerLDVR, integerMM, integerM, complex*16, dimension( * )WORK, double precision,
       dimension( * )RWORK, integerINFO)
       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 tranpose 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 Q (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.

       Date:
           November 2011

       Definition at line 219 of file ztgevc.f.

Author

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