CGEGS(1) LAPACK driver routine (version 3.2) CGEGS(1)NAME
CGEGS - routine i deprecated and has been replaced by routine CGGES
SYNOPSIS
SUBROUTINE CGEGS( JOBVSL, JOBVSR, N, A, LDA, B, LDB, ALPHA, BETA, VSL,
LDVSL, VSR, LDVSR, WORK, LWORK, RWORK, INFO )
CHARACTER JOBVSL, JOBVSR
INTEGER INFO, LDA, LDB, LDVSL, LDVSR, LWORK, N
REAL RWORK( * )
COMPLEX A( LDA, * ), ALPHA( * ), B( LDB, * ), BETA( * ), VSL(
LDVSL, * ), VSR( LDVSR, * ), WORK( * )
PURPOSE
This routine is deprecated and has been replaced by routine CGGES.
CGEGS 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 CGEGV
should be used instead. See CGEGV for a description of the eigenvalues
of the generalized nonsymmetric eigenvalue problem (GNEP).
ARGUMENTS
JOBVSL (input) CHARACTER*1
= 'N': do not compute the left Schur vectors;
= 'V': compute the left Schur vectors (returned in VSL).
JOBVSR (input) CHARACTER*1
= 'N': do not compute the right Schur vectors;
= 'V': compute the right Schur vectors (returned in VSR).
N (input) INTEGER
The order of the matrices A, B, VSL, and VSR. N >= 0.
A (input/output) COMPLEX array, dimension (LDA, N)
On entry, the matrix A. On exit, the upper triangular matrix S
from the generalized Schur factorization.
LDA (input) INTEGER
The leading dimension of A. LDA >= max(1,N).
B (input/output) COMPLEX array, dimension (LDB, N)
On entry, the matrix B. On exit, the upper triangular matrix T
from the generalized Schur factorization.
LDB (input) INTEGER
The leading dimension of B. LDB >= max(1,N).
ALPHA (output) COMPLEX 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 (output) COMPLEX 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 trian‐
gular 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 (output) COMPLEX array, dimension (LDVSL,N)
If JOBVSL = 'V', the matrix of left Schur vectors Q. Not ref‐
erenced if JOBVSL = 'N'.
LDVSL (input) INTEGER
The leading dimension of the matrix VSL. LDVSL >= 1, and if
JOBVSL = 'V', LDVSL >= N.
VSR (output) COMPLEX array, dimension (LDVSR,N)
If JOBVSR = 'V', the matrix of right Schur vectors Z. Not ref‐
erenced if JOBVSR = 'N'.
LDVSR (input) INTEGER
The leading dimension of the matrix VSR. LDVSR >= 1, and if
JOBVSR = 'V', LDVSR >= N.
WORK (workspace/output) COMPLEX array, dimension (MAX(1,LWORK))
On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
LWORK (input) 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
CGEQRF, CUNMQR, and CUNGQR.) Then compute: NB -- MAX of the
blocksizes for CGEQRF, CUNMQR, 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 (workspace) REAL array, dimension (3*N)
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 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 CGGBAL
=N+2: error return from CGEQRF
=N+3: error return from CUNMQR
=N+4: error return from CUNGQR
=N+5: error return from CGGHRD
=N+6: error return from CHGEQZ (other than failed iteration)
=N+7: error return from CGGBAK (computing VSL)
=N+8: error return from CGGBAK (computing VSR)
=N+9: error return from CLASCL (various places)
LAPACK driver routine (version 3November 2008 CGEGS(1)
