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SUBROUTINE ZGEES( JOBVS, SORT, SELECT, N, A, LDA, SDIM, W, VS,
$ LDVS, WORK, LWORK, RWORK, BWORK, INFO )
*
* -- LAPACK driver routine (version 3.1) --
* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
* November 2006
*
* .. Scalar Arguments ..
CHARACTER JOBVS, SORT
INTEGER INFO, LDA, LDVS, LWORK, N, SDIM
* ..
* .. Array Arguments ..
LOGICAL BWORK( * )
DOUBLE PRECISION RWORK( * )
COMPLEX*16 A( LDA, * ), VS( LDVS, * ), W( * ), WORK( * )
* ..
* .. Function Arguments ..
LOGICAL SELECT
EXTERNAL SELECT
* ..
*
* Purpose
* =======
*
* ZGEES computes for an N-by-N complex nonsymmetric matrix A, the
* eigenvalues, the Schur form T, and, optionally, the matrix of Schur
* vectors Z. This gives the Schur factorization A = Z*T*(Z**H).
*
* Optionally, it also orders the eigenvalues on the diagonal of the
* Schur form so that selected eigenvalues are at the top left.
* The leading columns of Z then form an orthonormal basis for the
* invariant subspace corresponding to the selected eigenvalues.
*
* A complex matrix is in Schur form if it is upper triangular.
*
* Arguments
* =========
*
* JOBVS (input) CHARACTER*1
* = 'N': Schur vectors are not computed;
* = 'V': Schur vectors are computed.
*
* SORT (input) CHARACTER*1
* Specifies whether or not to order the eigenvalues on the
* diagonal of the Schur form.
* = 'N': Eigenvalues are not ordered:
* = 'S': Eigenvalues are ordered (see SELECT).
*
* SELECT (external procedure) LOGICAL FUNCTION of one COMPLEX*16 argument
* SELECT must be declared EXTERNAL in the calling subroutine.
* If SORT = 'S', SELECT is used to select eigenvalues to order
* to the top left of the Schur form.
* IF SORT = 'N', SELECT is not referenced.
* The eigenvalue W(j) is selected if SELECT(W(j)) is true.
*
* N (input) INTEGER
* The order of the matrix A. N >= 0.
*
* A (input/output) COMPLEX*16 array, dimension (LDA,N)
* On entry, the N-by-N matrix A.
* On exit, A has been overwritten by its Schur form T.
*
* LDA (input) INTEGER
* The leading dimension of the array A. LDA >= max(1,N).
*
* SDIM (output) INTEGER
* If SORT = 'N', SDIM = 0.
* If SORT = 'S', SDIM = number of eigenvalues for which
* SELECT is true.
*
* W (output) COMPLEX*16 array, dimension (N)
* W contains the computed eigenvalues, in the same order that
* they appear on the diagonal of the output Schur form T.
*
* VS (output) COMPLEX*16 array, dimension (LDVS,N)
* If JOBVS = 'V', VS contains the unitary matrix Z of Schur
* vectors.
* If JOBVS = 'N', VS is not referenced.
*
* LDVS (input) INTEGER
* The leading dimension of the array VS. LDVS >= 1; if
* JOBVS = 'V', LDVS >= N.
*
* WORK (workspace/output) COMPLEX*16 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.
*
* 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) DOUBLE PRECISION array, dimension (N)
*
* BWORK (workspace) LOGICAL array, dimension (N)
* Not referenced if SORT = 'N'.
*
* INFO (output) INTEGER
* = 0: successful exit
* < 0: if INFO = -i, the i-th argument had an illegal value.
* > 0: if INFO = i, and i is
* <= N: the QR algorithm failed to compute all the
* eigenvalues; elements 1:ILO-1 and i+1:N of W
* contain those eigenvalues which have converged;
* if JOBVS = 'V', VS contains the matrix which
* reduces A to its partially converged Schur form.
* = N+1: the eigenvalues could not be reordered because
* some eigenvalues were too close to separate (the
* problem is very ill-conditioned);
* = N+2: after reordering, roundoff changed values of
* some complex eigenvalues so that leading
* eigenvalues in the Schur form no longer satisfy
* SELECT = .TRUE.. This could also be caused by
* underflow due to scaling.
*
* =====================================================================
*
* .. Parameters ..
DOUBLE PRECISION ZERO, ONE
PARAMETER ( ZERO = 0.0D0, ONE = 1.0D0 )
* ..
* .. Local Scalars ..
LOGICAL LQUERY, SCALEA, WANTST, WANTVS
INTEGER HSWORK, I, IBAL, ICOND, IERR, IEVAL, IHI, ILO,
$ ITAU, IWRK, MAXWRK, MINWRK
DOUBLE PRECISION ANRM, BIGNUM, CSCALE, EPS, S, SEP, SMLNUM
* ..
* .. Local Arrays ..
DOUBLE PRECISION DUM( 1 )
* ..
* .. External Subroutines ..
EXTERNAL DLABAD, XERBLA, ZCOPY, ZGEBAK, ZGEBAL, ZGEHRD,
$ ZHSEQR, ZLACPY, ZLASCL, ZTRSEN, ZUNGHR
* ..
* .. External Functions ..
LOGICAL LSAME
INTEGER ILAENV
DOUBLE PRECISION DLAMCH, ZLANGE
EXTERNAL LSAME, ILAENV, DLAMCH, ZLANGE
* ..
* .. Intrinsic Functions ..
INTRINSIC MAX, SQRT
* ..
* .. Executable Statements ..
*
* Test the input arguments
*
INFO = 0
LQUERY = ( LWORK.EQ.-1 )
WANTVS = LSAME( JOBVS, 'V' )
WANTST = LSAME( SORT, 'S' )
IF( ( .NOT.WANTVS ) .AND. ( .NOT.LSAME( JOBVS, 'N' ) ) ) THEN
INFO = -1
ELSE IF( ( .NOT.WANTST ) .AND. ( .NOT.LSAME( SORT, 'N' ) ) ) THEN
INFO = -2
ELSE IF( N.LT.0 ) THEN
INFO = -4
ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
INFO = -6
ELSE IF( LDVS.LT.1 .OR. ( WANTVS .AND. LDVS.LT.N ) ) THEN
INFO = -10
END IF
*
* Compute workspace
* (Note: Comments in the code beginning "Workspace:" describe the
* minimal amount of workspace needed at that point in the code,
* as well as the preferred amount for good performance.
* CWorkspace refers to complex workspace, and RWorkspace to real
* workspace. NB refers to the optimal block size for the
* immediately following subroutine, as returned by ILAENV.
* HSWORK refers to the workspace preferred by ZHSEQR, as
* calculated below. HSWORK is computed assuming ILO=1 and IHI=N,
* the worst case.)
*
IF( INFO.EQ.0 ) THEN
IF( N.EQ.0 ) THEN
MINWRK = 1
MAXWRK = 1
ELSE
MAXWRK = N + N*ILAENV( 1, 'ZGEHRD', ' ', N, 1, N, 0 )
MINWRK = 2*N
*
CALL ZHSEQR( 'S', JOBVS, N, 1, N, A, LDA, W, VS, LDVS,
$ WORK, -1, IEVAL )
HSWORK = WORK( 1 )
*
IF( .NOT.WANTVS ) THEN
MAXWRK = MAX( MAXWRK, HSWORK )
ELSE
MAXWRK = MAX( MAXWRK, N + ( N - 1 )*ILAENV( 1, 'ZUNGHR',
$ ' ', N, 1, N, -1 ) )
MAXWRK = MAX( MAXWRK, HSWORK )
END IF
END IF
WORK( 1 ) = MAXWRK
*
IF( LWORK.LT.MINWRK .AND. .NOT.LQUERY ) THEN
INFO = -12
END IF
END IF
*
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'ZGEES ', -INFO )
RETURN
ELSE IF( LQUERY ) THEN
RETURN
END IF
*
* Quick return if possible
*
IF( N.EQ.0 ) THEN
SDIM = 0
RETURN
END IF
*
* Get machine constants
*
EPS = DLAMCH( 'P' )
SMLNUM = DLAMCH( 'S' )
BIGNUM = ONE / SMLNUM
CALL DLABAD( SMLNUM, BIGNUM )
SMLNUM = SQRT( SMLNUM ) / EPS
BIGNUM = ONE / SMLNUM
*
* Scale A if max element outside range [SMLNUM,BIGNUM]
*
ANRM = ZLANGE( 'M', N, N, A, LDA, DUM )
SCALEA = .FALSE.
IF( ANRM.GT.ZERO .AND. ANRM.LT.SMLNUM ) THEN
SCALEA = .TRUE.
CSCALE = SMLNUM
ELSE IF( ANRM.GT.BIGNUM ) THEN
SCALEA = .TRUE.
CSCALE = BIGNUM
END IF
IF( SCALEA )
$ CALL ZLASCL( 'G', 0, 0, ANRM, CSCALE, N, N, A, LDA, IERR )
*
* Permute the matrix to make it more nearly triangular
* (CWorkspace: none)
* (RWorkspace: need N)
*
IBAL = 1
CALL ZGEBAL( 'P', N, A, LDA, ILO, IHI, RWORK( IBAL ), IERR )
*
* Reduce to upper Hessenberg form
* (CWorkspace: need 2*N, prefer N+N*NB)
* (RWorkspace: none)
*
ITAU = 1
IWRK = N + ITAU
CALL ZGEHRD( N, ILO, IHI, A, LDA, WORK( ITAU ), WORK( IWRK ),
$ LWORK-IWRK+1, IERR )
*
IF( WANTVS ) THEN
*
* Copy Householder vectors to VS
*
CALL ZLACPY( 'L', N, N, A, LDA, VS, LDVS )
*
* Generate unitary matrix in VS
* (CWorkspace: need 2*N-1, prefer N+(N-1)*NB)
* (RWorkspace: none)
*
CALL ZUNGHR( N, ILO, IHI, VS, LDVS, WORK( ITAU ), WORK( IWRK ),
$ LWORK-IWRK+1, IERR )
END IF
*
SDIM = 0
*
* Perform QR iteration, accumulating Schur vectors in VS if desired
* (CWorkspace: need 1, prefer HSWORK (see comments) )
* (RWorkspace: none)
*
IWRK = ITAU
CALL ZHSEQR( 'S', JOBVS, N, ILO, IHI, A, LDA, W, VS, LDVS,
$ WORK( IWRK ), LWORK-IWRK+1, IEVAL )
IF( IEVAL.GT.0 )
$ INFO = IEVAL
*
* Sort eigenvalues if desired
*
IF( WANTST .AND. INFO.EQ.0 ) THEN
IF( SCALEA )
$ CALL ZLASCL( 'G', 0, 0, CSCALE, ANRM, N, 1, W, N, IERR )
DO 10 I = 1, N
BWORK( I ) = SELECT( W( I ) )
10 CONTINUE
*
* Reorder eigenvalues and transform Schur vectors
* (CWorkspace: none)
* (RWorkspace: none)
*
CALL ZTRSEN( 'N', JOBVS, BWORK, N, A, LDA, VS, LDVS, W, SDIM,
$ S, SEP, WORK( IWRK ), LWORK-IWRK+1, ICOND )
END IF
*
IF( WANTVS ) THEN
*
* Undo balancing
* (CWorkspace: none)
* (RWorkspace: need N)
*
CALL ZGEBAK( 'P', 'R', N, ILO, IHI, RWORK( IBAL ), N, VS, LDVS,
$ IERR )
END IF
*
IF( SCALEA ) THEN
*
* Undo scaling for the Schur form of A
*
CALL ZLASCL( 'U', 0, 0, CSCALE, ANRM, N, N, A, LDA, IERR )
CALL ZCOPY( N, A, LDA+1, W, 1 )
END IF
*
WORK( 1 ) = MAXWRK
RETURN
*
* End of ZGEES
*
END
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