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cgges.f(3)				      LAPACK				       cgges.f(3)

NAME
       cgges.f -

SYNOPSIS
   Functions/Subroutines
       subroutine cgges (JOBVSL, JOBVSR, SORT, SELCTG, N, A, LDA, B, LDB, SDIM, ALPHA, BETA, VSL,
	   LDVSL, VSR, LDVSR, WORK, LWORK, RWORK, BWORK, INFO)
	    CGGES computes the eigenvalues, the Schur form, and, optionally, the matrix of Schur
	   vectors for GE matrices

Function/Subroutine Documentation
   subroutine cgges (characterJOBVSL, characterJOBVSR, characterSORT, logical, externalSELCTG,
       integerN, complex, dimension( lda, * )A, integerLDA, complex, dimension( ldb, * )B,
       integerLDB, integerSDIM, complex, dimension( * )ALPHA, complex, dimension( * )BETA,
       complex, dimension( ldvsl, * )VSL, integerLDVSL, complex, dimension( ldvsr, * )VSR,
       integerLDVSR, complex, dimension( * )WORK, integerLWORK, real, dimension( * )RWORK,
       logical, dimension( * )BWORK, integerINFO)
	CGGES computes the eigenvalues, the Schur form, and, optionally, the matrix of Schur
       vectors for GE matrices

       Purpose:

	    CGGES computes for a pair of N-by-N complex nonsymmetric matrices
	    (A,B), the generalized eigenvalues, the generalized complex Schur
	    form (S, T), and optionally left and/or right Schur vectors (VSL
	    and VSR). This gives the generalized Schur factorization

		    (A,B) = ( (VSL)*S*(VSR)**H, (VSL)*T*(VSR)**H )

	    where (VSR)**H is the conjugate-transpose of VSR.

	    Optionally, it also orders the eigenvalues so that a selected cluster
	    of eigenvalues appears in the leading diagonal blocks of the upper
	    triangular matrix S and the upper triangular matrix T. The leading
	    columns of VSL and VSR then form an unitary basis for the
	    corresponding left and right eigenspaces (deflating subspaces).

	    (If only the generalized eigenvalues are needed, use the driver
	    CGGEV instead, which is faster.)

	    A generalized eigenvalue for a pair of matrices (A,B) is a scalar w
	    or a ratio alpha/beta = w, such that  A - w*B is singular.	It is
	    usually represented as the pair (alpha,beta), as there is a
	    reasonable interpretation for beta=0, and even for both being zero.

	    A pair of matrices (S,T) is in generalized complex Schur form if S
	    and T are upper triangular and, in addition, the diagonal elements
	    of T are non-negative real numbers.

       Parameters:
	   JOBVSL

		     JOBVSL is CHARACTER*1
		     = 'N':  do not compute the left Schur vectors;
		     = 'V':  compute the left Schur vectors.

	   JOBVSR

		     JOBVSR is CHARACTER*1
		     = 'N':  do not compute the right Schur vectors;
		     = 'V':  compute the right Schur vectors.

	   SORT

		     SORT is CHARACTER*1
		     Specifies whether or not to order the eigenvalues on the
		     diagonal of the generalized Schur form.
		     = 'N':  Eigenvalues are not ordered;
		     = 'S':  Eigenvalues are ordered (see SELCTG).

	   SELCTG

		     SELCTG is a LOGICAL FUNCTION of two COMPLEX arguments
		     SELCTG must be declared EXTERNAL in the calling subroutine.
		     If SORT = 'N', SELCTG is not referenced.
		     If SORT = 'S', SELCTG is used to select eigenvalues to sort
		     to the top left of the Schur form.
		     An eigenvalue ALPHA(j)/BETA(j) is selected if
		     SELCTG(ALPHA(j),BETA(j)) is true.

		     Note that a selected complex eigenvalue may no longer satisfy
		     SELCTG(ALPHA(j),BETA(j)) = .TRUE. after ordering, since
		     ordering may change the value of complex eigenvalues
		     (especially if the eigenvalue is ill-conditioned), in this
		     case INFO is set to N+2 (See INFO below).

	   N

		     N is INTEGER
		     The order of the matrices A, B, VSL, and VSR.  N >= 0.

	   A

		     A is COMPLEX array, dimension (LDA, N)
		     On entry, the first of the pair of matrices.
		     On exit, A has been overwritten by its generalized Schur
		     form S.

	   LDA

		     LDA is INTEGER
		     The leading dimension of A.  LDA >= max(1,N).

	   B

		     B is COMPLEX array, dimension (LDB, N)
		     On entry, the second of the pair of matrices.
		     On exit, B has been overwritten by its generalized Schur
		     form T.

	   LDB

		     LDB is INTEGER
		     The leading dimension of B.  LDB >= max(1,N).

	   SDIM

		     SDIM is INTEGER
		     If SORT = 'N', SDIM = 0.
		     If SORT = 'S', SDIM = number of eigenvalues (after sorting)
		     for which SELCTG is true.

	   ALPHA

		     ALPHA is COMPLEX array, dimension (N)

	   BETA

		     BETA is COMPLEX array, dimension (N)
		     On exit,  ALPHA(j)/BETA(j), j=1,...,N, will be the
		     generalized eigenvalues.  ALPHA(j), j=1,...,N  and  BETA(j),
		     j=1,...,N	are the diagonals of the complex Schur form (A,B)
		     output by CGGES. The  BETA(j) will be non-negative real.

		     Note: the quotients ALPHA(j)/BETA(j) may easily over- or
		     underflow, and BETA(j) may even be zero.  Thus, the user
		     should avoid naively computing the ratio alpha/beta.
		     However, ALPHA will be always less than and usually
		     comparable with norm(A) in magnitude, and BETA always less
		     than and usually comparable with norm(B).

	   VSL

		     VSL is COMPLEX array, dimension (LDVSL,N)
		     If JOBVSL = 'V', VSL will contain the left Schur vectors.
		     Not referenced if JOBVSL = 'N'.

	   LDVSL

		     LDVSL is INTEGER
		     The leading dimension of the matrix VSL. LDVSL >= 1, and
		     if JOBVSL = 'V', LDVSL >= N.

	   VSR

		     VSR is COMPLEX array, dimension (LDVSR,N)
		     If JOBVSR = 'V', VSR will contain the right Schur vectors.
		     Not referenced if JOBVSR = 'N'.

	   LDVSR

		     LDVSR is INTEGER
		     The leading dimension of the matrix VSR. LDVSR >= 1, and
		     if JOBVSR = 'V', LDVSR >= N.

	   WORK

		     WORK is COMPLEX array, dimension (MAX(1,LWORK))
		     On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

	   LWORK

		     LWORK is INTEGER
		     The dimension of the array WORK.  LWORK >= max(1,2*N).
		     For good performance, LWORK must generally be larger.

		     If LWORK = -1, then a workspace query is assumed; the routine
		     only calculates the optimal size of the WORK array, returns
		     this value as the first entry of the WORK array, and no error
		     message related to LWORK is issued by XERBLA.

	   RWORK

		     RWORK is REAL array, dimension (8*N)

	   BWORK

		     BWORK is LOGICAL array, dimension (N)
		     Not referenced if SORT = 'N'.

	   INFO

		     INFO is INTEGER
		     = 0:  successful exit
		     < 0:  if INFO = -i, the i-th argument had an illegal value.
		     =1,...,N:
			   The QZ iteration failed.  (A,B) are not in Schur
			   form, but ALPHA(j) and BETA(j) should be correct for
			   j=INFO+1,...,N.
		     > N:  =N+1: other than QZ iteration failed in CHGEQZ
			   =N+2: after reordering, roundoff changed values of
				 some complex eigenvalues so that leading
				 eigenvalues in the Generalized Schur form no
				 longer satisfy SELCTG=.TRUE.  This could also
				 be caused due to scaling.
			   =N+3: reordering falied in CTGSEN.

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   November 2011

       Definition at line 269 of file cgges.f.

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

Version 3.4.2				 Tue Sep 25 2012			       cgges.f(3)
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