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zgegs.f(3) LAPACK zgegs.f(3)

zgegs.f -


subroutine zgegs (JOBVSL, JOBVSR, N, A, LDA, B, LDB, ALPHA, BETA, VSL, LDVSL, VSR, LDVSR, WORK, LWORK, RWORK, INFO)
 
ZGEEVX computes the eigenvalues and, optionally, the left and/or right eigenvectors for GE matrices

ZGEEVX computes the eigenvalues and, optionally, the left and/or right eigenvectors for GE matrices
Purpose:
 This routine is deprecated and has been replaced by routine ZGGES.
ZGEGS computes the eigenvalues, Schur form, and, optionally, the left and or/right Schur vectors of a complex matrix pair (A,B). Given two square matrices A and B, the generalized Schur factorization has the form A = Q*S*Z**H, B = Q*T*Z**H where Q and Z are unitary matrices and S and T are upper triangular. The columns of Q are the left Schur vectors and the columns of Z are the right Schur vectors. If only the eigenvalues of (A,B) are needed, the driver routine ZGEGV should be used instead. See ZGEGV for a description of the eigenvalues of the generalized nonsymmetric eigenvalue problem (GNEP).
Parameters:
JOBVSL
          JOBVSL is CHARACTER*1
          = 'N':  do not compute the left Schur vectors;
          = 'V':  compute the left Schur vectors (returned in VSL).
JOBVSR
          JOBVSR is CHARACTER*1
          = 'N':  do not compute the right Schur vectors;
          = 'V':  compute the right Schur vectors (returned in VSR).
N
          N is INTEGER
          The order of the matrices A, B, VSL, and VSR.  N >= 0.
A
          A is COMPLEX*16 array, dimension (LDA, N)
          On entry, the matrix A.
          On exit, the upper triangular matrix S from the generalized
          Schur factorization.
LDA
          LDA is INTEGER
          The leading dimension of A.  LDA >= max(1,N).
B
          B is COMPLEX*16 array, dimension (LDB, N)
          On entry, the matrix B.
          On exit, the upper triangular matrix T from the generalized
          Schur factorization.
LDB
          LDB is INTEGER
          The leading dimension of B.  LDB >= max(1,N).
ALPHA
          ALPHA is COMPLEX*16 array, dimension (N)
          The complex scalars alpha that define the eigenvalues of
          GNEP.  ALPHA(j) = S(j,j), the diagonal element of the Schur
          form of A.
BETA
          BETA is COMPLEX*16 array, dimension (N)
          The non-negative real scalars beta that define the
          eigenvalues of GNEP.  BETA(j) = T(j,j), the diagonal element
          of the triangular factor T.
Together, the quantities alpha = ALPHA(j) and beta = BETA(j) represent the j-th eigenvalue of the matrix pair (A,B), in one of the forms lambda = alpha/beta or mu = beta/alpha. Since either lambda or mu may overflow, they should not, in general, be computed.
VSL
          VSL is COMPLEX*16 array, dimension (LDVSL,N)
          If JOBVSL = 'V', the matrix of left Schur vectors Q.
          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*16 array, dimension (LDVSR,N)
          If JOBVSR = 'V', the matrix of right Schur vectors Z.
          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*16 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.
          To compute the optimal value of LWORK, call ILAENV to get
          blocksizes (for ZGEQRF, ZUNMQR, and CUNGQR.)  Then compute:
          NB  -- MAX of the blocksizes for ZGEQRF, ZUNMQR, and CUNGQR;
          the optimal LWORK is 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.
RWORK
          RWORK is DOUBLE PRECISION array, dimension (3*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:  errors that usually indicate LAPACK problems:
                =N+1: error return from ZGGBAL
                =N+2: error return from ZGEQRF
                =N+3: error return from ZUNMQR
                =N+4: error return from ZUNGQR
                =N+5: error return from ZGGHRD
                =N+6: error return from ZHGEQZ (other than failed
                                               iteration)
                =N+7: error return from ZGGBAK (computing VSL)
                =N+8: error return from ZGGBAK (computing VSR)
                =N+9: error return from ZLASCL (various places)
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011
Definition at line 224 of file zgegs.f.

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Sat Nov 16 2013 Version 3.4.2

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