LAPACK  3.8.0
LAPACK: Linear Algebra PACKage

◆ zgees()

subroutine zgees ( character  JOBVS,
character  SORT,
external  SELECT,
integer  N,
complex*16, dimension( lda, * )  A,
integer  LDA,
integer  SDIM,
complex*16, dimension( * )  W,
complex*16, dimension( ldvs, * )  VS,
integer  LDVS,
complex*16, dimension( * )  WORK,
integer  LWORK,
double precision, dimension( * )  RWORK,
logical, dimension( * )  BWORK,
integer  INFO 
)

ZGEES computes the eigenvalues, the Schur form, and, optionally, the matrix of Schur vectors for GE matrices

Download ZGEES + dependencies [TGZ] [ZIP] [TXT]

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.
Parameters
[in]JOBVS
          JOBVS is CHARACTER*1
          = 'N': Schur vectors are not computed;
          = 'V': Schur vectors are computed.
[in]SORT
          SORT is 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).
[in]SELECT
          SELECT is a 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.
[in]N
          N is INTEGER
          The order of the matrix A. N >= 0.
[in,out]A
          A is 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.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.  LDA >= max(1,N).
[out]SDIM
          SDIM is INTEGER
          If SORT = 'N', SDIM = 0.
          If SORT = 'S', SDIM = number of eigenvalues for which
                         SELECT is true.
[out]W
          W is 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.
[out]VS
          VS is 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.
[in]LDVS
          LDVS is INTEGER
          The leading dimension of the array VS.  LDVS >= 1; if
          JOBVS = 'V', LDVS >= N.
[out]WORK
          WORK is COMPLEX*16 array, dimension (MAX(1,LWORK))
          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
[in]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.
[out]RWORK
          RWORK is DOUBLE PRECISION array, dimension (N)
[out]BWORK
          BWORK is LOGICAL array, dimension (N)
          Not referenced if SORT = 'N'.
[out]INFO
          INFO is 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.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
December 2016

Definition at line 199 of file zgees.f.

199 *
200 * -- LAPACK driver routine (version 3.7.0) --
201 * -- LAPACK is a software package provided by Univ. of Tennessee, --
202 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
203 * December 2016
204 *
205 * .. Scalar Arguments ..
206  CHARACTER jobvs, sort
207  INTEGER info, lda, ldvs, lwork, n, sdim
208 * ..
209 * .. Array Arguments ..
210  LOGICAL bwork( * )
211  DOUBLE PRECISION rwork( * )
212  COMPLEX*16 a( lda, * ), vs( ldvs, * ), w( * ), work( * )
213 * ..
214 * .. Function Arguments ..
215  LOGICAL select
216  EXTERNAL SELECT
217 * ..
218 *
219 * =====================================================================
220 *
221 * .. Parameters ..
222  DOUBLE PRECISION zero, one
223  parameter( zero = 0.0d0, one = 1.0d0 )
224 * ..
225 * .. Local Scalars ..
226  LOGICAL lquery, scalea, wantst, wantvs
227  INTEGER hswork, i, ibal, icond, ierr, ieval, ihi, ilo,
228  $ itau, iwrk, maxwrk, minwrk
229  DOUBLE PRECISION anrm, bignum, cscale, eps, s, sep, smlnum
230 * ..
231 * .. Local Arrays ..
232  DOUBLE PRECISION dum( 1 )
233 * ..
234 * .. External Subroutines ..
235  EXTERNAL dlabad, xerbla, zcopy, zgebak, zgebal, zgehrd,
237 * ..
238 * .. External Functions ..
239  LOGICAL lsame
240  INTEGER ilaenv
241  DOUBLE PRECISION dlamch, zlange
242  EXTERNAL lsame, ilaenv, dlamch, zlange
243 * ..
244 * .. Intrinsic Functions ..
245  INTRINSIC max, sqrt
246 * ..
247 * .. Executable Statements ..
248 *
249 * Test the input arguments
250 *
251  info = 0
252  lquery = ( lwork.EQ.-1 )
253  wantvs = lsame( jobvs, 'V' )
254  wantst = lsame( sort, 'S' )
255  IF( ( .NOT.wantvs ) .AND. ( .NOT.lsame( jobvs, 'N' ) ) ) THEN
256  info = -1
257  ELSE IF( ( .NOT.wantst ) .AND. ( .NOT.lsame( sort, 'N' ) ) ) THEN
258  info = -2
259  ELSE IF( n.LT.0 ) THEN
260  info = -4
261  ELSE IF( lda.LT.max( 1, n ) ) THEN
262  info = -6
263  ELSE IF( ldvs.LT.1 .OR. ( wantvs .AND. ldvs.LT.n ) ) THEN
264  info = -10
265  END IF
266 *
267 * Compute workspace
268 * (Note: Comments in the code beginning "Workspace:" describe the
269 * minimal amount of workspace needed at that point in the code,
270 * as well as the preferred amount for good performance.
271 * CWorkspace refers to complex workspace, and RWorkspace to real
272 * workspace. NB refers to the optimal block size for the
273 * immediately following subroutine, as returned by ILAENV.
274 * HSWORK refers to the workspace preferred by ZHSEQR, as
275 * calculated below. HSWORK is computed assuming ILO=1 and IHI=N,
276 * the worst case.)
277 *
278  IF( info.EQ.0 ) THEN
279  IF( n.EQ.0 ) THEN
280  minwrk = 1
281  maxwrk = 1
282  ELSE
283  maxwrk = n + n*ilaenv( 1, 'ZGEHRD', ' ', n, 1, n, 0 )
284  minwrk = 2*n
285 *
286  CALL zhseqr( 'S', jobvs, n, 1, n, a, lda, w, vs, ldvs,
287  $ work, -1, ieval )
288  hswork = work( 1 )
289 *
290  IF( .NOT.wantvs ) THEN
291  maxwrk = max( maxwrk, hswork )
292  ELSE
293  maxwrk = max( maxwrk, n + ( n - 1 )*ilaenv( 1, 'ZUNGHR',
294  $ ' ', n, 1, n, -1 ) )
295  maxwrk = max( maxwrk, hswork )
296  END IF
297  END IF
298  work( 1 ) = maxwrk
299 *
300  IF( lwork.LT.minwrk .AND. .NOT.lquery ) THEN
301  info = -12
302  END IF
303  END IF
304 *
305  IF( info.NE.0 ) THEN
306  CALL xerbla( 'ZGEES ', -info )
307  RETURN
308  ELSE IF( lquery ) THEN
309  RETURN
310  END IF
311 *
312 * Quick return if possible
313 *
314  IF( n.EQ.0 ) THEN
315  sdim = 0
316  RETURN
317  END IF
318 *
319 * Get machine constants
320 *
321  eps = dlamch( 'P' )
322  smlnum = dlamch( 'S' )
323  bignum = one / smlnum
324  CALL dlabad( smlnum, bignum )
325  smlnum = sqrt( smlnum ) / eps
326  bignum = one / smlnum
327 *
328 * Scale A if max element outside range [SMLNUM,BIGNUM]
329 *
330  anrm = zlange( 'M', n, n, a, lda, dum )
331  scalea = .false.
332  IF( anrm.GT.zero .AND. anrm.LT.smlnum ) THEN
333  scalea = .true.
334  cscale = smlnum
335  ELSE IF( anrm.GT.bignum ) THEN
336  scalea = .true.
337  cscale = bignum
338  END IF
339  IF( scalea )
340  $ CALL zlascl( 'G', 0, 0, anrm, cscale, n, n, a, lda, ierr )
341 *
342 * Permute the matrix to make it more nearly triangular
343 * (CWorkspace: none)
344 * (RWorkspace: need N)
345 *
346  ibal = 1
347  CALL zgebal( 'P', n, a, lda, ilo, ihi, rwork( ibal ), ierr )
348 *
349 * Reduce to upper Hessenberg form
350 * (CWorkspace: need 2*N, prefer N+N*NB)
351 * (RWorkspace: none)
352 *
353  itau = 1
354  iwrk = n + itau
355  CALL zgehrd( n, ilo, ihi, a, lda, work( itau ), work( iwrk ),
356  $ lwork-iwrk+1, ierr )
357 *
358  IF( wantvs ) THEN
359 *
360 * Copy Householder vectors to VS
361 *
362  CALL zlacpy( 'L', n, n, a, lda, vs, ldvs )
363 *
364 * Generate unitary matrix in VS
365 * (CWorkspace: need 2*N-1, prefer N+(N-1)*NB)
366 * (RWorkspace: none)
367 *
368  CALL zunghr( n, ilo, ihi, vs, ldvs, work( itau ), work( iwrk ),
369  $ lwork-iwrk+1, ierr )
370  END IF
371 *
372  sdim = 0
373 *
374 * Perform QR iteration, accumulating Schur vectors in VS if desired
375 * (CWorkspace: need 1, prefer HSWORK (see comments) )
376 * (RWorkspace: none)
377 *
378  iwrk = itau
379  CALL zhseqr( 'S', jobvs, n, ilo, ihi, a, lda, w, vs, ldvs,
380  $ work( iwrk ), lwork-iwrk+1, ieval )
381  IF( ieval.GT.0 )
382  $ info = ieval
383 *
384 * Sort eigenvalues if desired
385 *
386  IF( wantst .AND. info.EQ.0 ) THEN
387  IF( scalea )
388  $ CALL zlascl( 'G', 0, 0, cscale, anrm, n, 1, w, n, ierr )
389  DO 10 i = 1, n
390  bwork( i ) = SELECT( w( i ) )
391  10 CONTINUE
392 *
393 * Reorder eigenvalues and transform Schur vectors
394 * (CWorkspace: none)
395 * (RWorkspace: none)
396 *
397  CALL ztrsen( 'N', jobvs, bwork, n, a, lda, vs, ldvs, w, sdim,
398  $ s, sep, work( iwrk ), lwork-iwrk+1, icond )
399  END IF
400 *
401  IF( wantvs ) THEN
402 *
403 * Undo balancing
404 * (CWorkspace: none)
405 * (RWorkspace: need N)
406 *
407  CALL zgebak( 'P', 'R', n, ilo, ihi, rwork( ibal ), n, vs, ldvs,
408  $ ierr )
409  END IF
410 *
411  IF( scalea ) THEN
412 *
413 * Undo scaling for the Schur form of A
414 *
415  CALL zlascl( 'U', 0, 0, cscale, anrm, n, n, a, lda, ierr )
416  CALL zcopy( n, a, lda+1, w, 1 )
417  END IF
418 *
419  work( 1 ) = maxwrk
420  RETURN
421 *
422 * End of ZGEES
423 *
double precision function dlamch(CMACH)
DLAMCH
Definition: dlamch.f:65
subroutine zcopy(N, ZX, INCX, ZY, INCY)
ZCOPY
Definition: zcopy.f:83
subroutine zgehrd(N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO)
ZGEHRD
Definition: zgehrd.f:169
subroutine zlascl(TYPE, KL, KU, CFROM, CTO, M, N, A, LDA, INFO)
ZLASCL multiplies a general rectangular matrix by a real scalar defined as cto/cfrom.
Definition: zlascl.f:145
subroutine zlacpy(UPLO, M, N, A, LDA, B, LDB)
ZLACPY copies all or part of one two-dimensional array to another.
Definition: zlacpy.f:105
integer function ilaenv(ISPEC, NAME, OPTS, N1, N2, N3, N4)
ILAENV
Definition: tstiee.f:83
subroutine zunghr(N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO)
ZUNGHR
Definition: zunghr.f:128
double precision function zlange(NORM, M, N, A, LDA, WORK)
ZLANGE returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value ...
Definition: zlange.f:117
subroutine zgebal(JOB, N, A, LDA, ILO, IHI, SCALE, INFO)
ZGEBAL
Definition: zgebal.f:164
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:55
subroutine dlabad(SMALL, LARGE)
DLABAD
Definition: dlabad.f:76
subroutine zgebak(JOB, SIDE, N, ILO, IHI, SCALE, M, V, LDV, INFO)
ZGEBAK
Definition: zgebak.f:133
subroutine ztrsen(JOB, COMPQ, SELECT, N, T, LDT, Q, LDQ, W, M, S, SEP, WORK, LWORK, INFO)
ZTRSEN
Definition: ztrsen.f:266
subroutine zhseqr(JOB, COMPZ, N, ILO, IHI, H, LDH, W, Z, LDZ, WORK, LWORK, INFO)
ZHSEQR
Definition: zhseqr.f:301
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