CXML
        	    
LAPACK version 3.0
dgegs(3)

PURPOSE
  DGEGS - routine is deprecated and has been replaced by routine DGGES

SYNTAX
  SUBROUTINE DGEGS( JOBVSL, JOBVSR, N, A, LDA, B, LDB, ALPHAR, ALPHAI, BETA,
		    VSL, LDVSL, VSR, LDVSR, WORK, LWORK, INFO )

      CHARACTER	    JOBVSL, JOBVSR

      INTEGER	    INFO, LDA, LDB, LDVSL, LDVSR, LWORK, N

      DOUBLE	    PRECISION A( LDA, * ), ALPHAI( * ), ALPHAR( * ), B( LDB,
		    * ), BETA( * ), VSL( LDVSL, * ), VSR( LDVSR, * ), WORK( *
		    )

DESCRIPTION
  This routine is deprecated and has been replaced by routine DGGES.  DGEGS
  computes for a pair of N-by-N real nonsymmetric matrices A, B: the
  generalized eigenvalues (alphar +/- alphai*i, beta), the real Schur form
  (A, B), and optionally left and/or right Schur vectors (VSL and VSR).

  (If only the generalized eigenvalues are needed, use the driver DGEGV
  instead.)

  A generalized eigenvalue for a pair of matrices (A,B) is, roughly speaking,
  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 good beginning
  reference is the book, "Matrix Computations", by G. Golub & C. van Loan
  (Johns Hopkins U. Press)

  The (generalized) Schur form of a pair of matrices is the result of
  multiplying both matrices on the left by one orthogonal matrix and both on
  the right by another orthogonal matrix, these two orthogonal matrices being
  chosen so as to bring the pair of matrices into (real) Schur form.

  A pair of matrices A, B is in generalized real Schur form if B is upper
  triangular with non-negative diagonal and A is block upper triangular with
  1-by-1 and 2-by-2 blocks.  1-by-1 blocks correspond to real generalized
  eigenvalues, while 2-by-2 blocks of A will be "standardized" by making the
  corresponding elements of B have the form:
	  [  a	0  ]
	  [  0	b  ]

  and the pair of corresponding 2-by-2 blocks in A and B will have a complex
  conjugate pair of generalized eigenvalues.

  The left and right Schur vectors are the columns of VSL and VSR,
  respectively, where VSL and VSR are the orthogonal matrices which reduce A
  and B to Schur form:

  Schur form of (A,B) = ( (VSL)**T A (VSR), (VSL)**T B (VSR) )

ARGUMENTS
  JOBVSL  (input) CHARACTER*1
	  = 'N':  do not compute the left Schur vectors;
	  = 'V':  compute the left Schur vectors.

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

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

  A	  (input/output) DOUBLE PRECISION array, dimension (LDA, N)
	  On entry, the first of the pair of matrices whose generalized
	  eigenvalues and (optionally) Schur vectors are to be computed.  On
	  exit, the generalized Schur form of A.  Note: to avoid overflow,
	  the Frobenius norm of the matrix A should be less than the overflow
	  threshold.

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

  B	  (input/output) DOUBLE PRECISION array, dimension (LDB, N)
	  On entry, the second of the pair of matrices whose generalized
	  eigenvalues and (optionally) Schur vectors are to be computed.  On
	  exit, the generalized Schur form of B.  Note: to avoid overflow,
	  the Frobenius norm of the matrix B should be less than the overflow
	  threshold.

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

  ALPHAR  (output) DOUBLE PRECISION array, dimension (N)
	  ALPHAI  (output) DOUBLE PRECISION array, dimension (N) BETA
	  (output) DOUBLE PRECISION array, dimension (N) On exit, (ALPHAR(j)
	  + ALPHAI(j)*i)/BETA(j), j=1,...,N, will be the generalized
	  eigenvalues.	ALPHAR(j) + ALPHAI(j)*i, j=1,...,N  and
	  BETA(j),j=1,...,N  are the diagonals of the complex Schur form
	  (A,B) that would result if the 2-by-2 diagonal blocks of the real
	  Schur form of (A,B) were further reduced to triangular form using
	  2-by-2 complex unitary transformations.  If ALPHAI(j) is zero, then
	  the j-th eigenvalue is real; if positive, then the j-th and (j+1)-
	  st eigenvalues are a complex conjugate pair, with ALPHAI(j+1)
	  negative.

	  Note: the quotients ALPHAR(j)/BETA(j) and ALPHAI(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,
	  ALPHAR and ALPHAI 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	  (output) DOUBLE PRECISION array, dimension (LDVSL,N)
	  If JOBVSL = 'V', VSL will contain the left Schur vectors.  (See
	  "Purpose", above.) Not referenced if JOBVSL = 'N'.

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

  VSR	  (output) DOUBLE PRECISION array, dimension (LDVSR,N)
	  If JOBVSR = 'V', VSR will contain the right Schur vectors.  (See
	  "Purpose", above.) Not referenced if JOBVSR = 'N'.

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

  WORK	  (workspace/output) DOUBLE PRECISION array, dimension (LWORK)
	  On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

  LWORK	  (input) INTEGER
	  The dimension of the array WORK.  LWORK >= max(1,4*N).  For good
	  performance, LWORK must generally be larger.	To compute the
	  optimal value of LWORK, call ILAENV to get blocksizes (for DGEQRF,
	  DORMQR, and DORGQR.)	Then compute: NB  -- MAX of the blocksizes
	  for DGEQRF, DORMQR, and DORGQR The optimal LWORK is  2*N +
	  N*(NB+1).

	  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.

  INFO	  (output) 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 ALPHAR(j), ALPHAI(j), and BETA(j) should be correct for
	  j=INFO+1,...,N.  > N:	 errors that usually indicate LAPACK
	  problems:
	  =N+1: error return from DGGBAL
	  =N+2: error return from DGEQRF
	  =N+3: error return from DORMQR
	  =N+4: error return from DORGQR
	  =N+5: error return from DGGHRD
	  =N+6: error return from DHGEQZ (other than failed iteration) =N+7:
	  error return from DGGBAK (computing VSL)
	  =N+8: error return from DGGBAK (computing VSR)
	  =N+9: error return from DLASCL (various places)