LAPACK  3.9.1
LAPACK: Linear Algebra PACKage

◆ zlaqr0()

subroutine zlaqr0 ( logical  WANTT,
logical  WANTZ,
integer  N,
integer  ILO,
integer  IHI,
complex*16, dimension( ldh, * )  H,
integer  LDH,
complex*16, dimension( * )  W,
integer  ILOZ,
integer  IHIZ,
complex*16, dimension( ldz, * )  Z,
integer  LDZ,
complex*16, dimension( * )  WORK,
integer  LWORK,
integer  INFO 
)

ZLAQR0 computes the eigenvalues of a Hessenberg matrix, and optionally the matrices from the Schur decomposition.

Download ZLAQR0 + dependencies [TGZ] [ZIP] [TXT]

Purpose:
    ZLAQR0 computes the eigenvalues of a Hessenberg matrix H
    and, optionally, the matrices T and Z from the Schur decomposition
    H = Z T Z**H, where T is an upper triangular matrix (the
    Schur form), and Z is the unitary matrix of Schur vectors.

    Optionally Z may be postmultiplied into an input unitary
    matrix Q so that this routine can give the Schur factorization
    of a matrix A which has been reduced to the Hessenberg form H
    by the unitary matrix Q:  A = Q*H*Q**H = (QZ)*H*(QZ)**H.
Parameters
[in]WANTT
          WANTT is LOGICAL
          = .TRUE. : the full Schur form T is required;
          = .FALSE.: only eigenvalues are required.
[in]WANTZ
          WANTZ is LOGICAL
          = .TRUE. : the matrix of Schur vectors Z is required;
          = .FALSE.: Schur vectors are not required.
[in]N
          N is INTEGER
           The order of the matrix H.  N >= 0.
[in]ILO
          ILO is INTEGER
[in]IHI
          IHI is INTEGER

           It is assumed that H is already upper triangular in rows
           and columns 1:ILO-1 and IHI+1:N and, if ILO > 1,
           H(ILO,ILO-1) is zero. ILO and IHI are normally set by a
           previous call to ZGEBAL, and then passed to ZGEHRD when the
           matrix output by ZGEBAL is reduced to Hessenberg form.
           Otherwise, ILO and IHI should be set to 1 and N,
           respectively.  If N > 0, then 1 <= ILO <= IHI <= N.
           If N = 0, then ILO = 1 and IHI = 0.
[in,out]H
          H is COMPLEX*16 array, dimension (LDH,N)
           On entry, the upper Hessenberg matrix H.
           On exit, if INFO = 0 and WANTT is .TRUE., then H
           contains the upper triangular matrix T from the Schur
           decomposition (the Schur form). If INFO = 0 and WANT is
           .FALSE., then the contents of H are unspecified on exit.
           (The output value of H when INFO > 0 is given under the
           description of INFO below.)

           This subroutine may explicitly set H(i,j) = 0 for i > j and
           j = 1, 2, ... ILO-1 or j = IHI+1, IHI+2, ... N.
[in]LDH
          LDH is INTEGER
           The leading dimension of the array H. LDH >= max(1,N).
[out]W
          W is COMPLEX*16 array, dimension (N)
           The computed eigenvalues of H(ILO:IHI,ILO:IHI) are stored
           in W(ILO:IHI). If WANTT is .TRUE., then the eigenvalues are
           stored in the same order as on the diagonal of the Schur
           form returned in H, with W(i) = H(i,i).
[in]ILOZ
          ILOZ is INTEGER
[in]IHIZ
          IHIZ is INTEGER
           Specify the rows of Z to which transformations must be
           applied if WANTZ is .TRUE..
           1 <= ILOZ <= ILO; IHI <= IHIZ <= N.
[in,out]Z
          Z is COMPLEX*16 array, dimension (LDZ,IHI)
           If WANTZ is .FALSE., then Z is not referenced.
           If WANTZ is .TRUE., then Z(ILO:IHI,ILOZ:IHIZ) is
           replaced by Z(ILO:IHI,ILOZ:IHIZ)*U where U is the
           orthogonal Schur factor of H(ILO:IHI,ILO:IHI).
           (The output value of Z when INFO > 0 is given under
           the description of INFO below.)
[in]LDZ
          LDZ is INTEGER
           The leading dimension of the array Z.  if WANTZ is .TRUE.
           then LDZ >= MAX(1,IHIZ).  Otherwise, LDZ >= 1.
[out]WORK
          WORK is COMPLEX*16 array, dimension LWORK
           On exit, if LWORK = -1, WORK(1) returns an estimate of
           the optimal value for LWORK.
[in]LWORK
          LWORK is INTEGER
           The dimension of the array WORK.  LWORK >= max(1,N)
           is sufficient, but LWORK typically as large as 6*N may
           be required for optimal performance.  A workspace query
           to determine the optimal workspace size is recommended.

           If LWORK = -1, then ZLAQR0 does a workspace query.
           In this case, ZLAQR0 checks the input parameters and
           estimates the optimal workspace size for the given
           values of N, ILO and IHI.  The estimate is returned
           in WORK(1).  No error message related to LWORK is
           issued by XERBLA.  Neither H nor Z are accessed.
[out]INFO
          INFO is INTEGER
             = 0:  successful exit
             > 0:  if INFO = i, ZLAQR0 failed to compute all of
                the eigenvalues.  Elements 1:ilo-1 and i+1:n of WR
                and WI contain those eigenvalues which have been
                successfully computed.  (Failures are rare.)

                If INFO > 0 and WANT is .FALSE., then on exit,
                the remaining unconverged eigenvalues are the eigen-
                values of the upper Hessenberg matrix rows and
                columns ILO through INFO of the final, output
                value of H.

                If INFO > 0 and WANTT is .TRUE., then on exit

           (*)  (initial value of H)*U  = U*(final value of H)

                where U is a unitary matrix.  The final
                value of  H is upper Hessenberg and triangular in
                rows and columns INFO+1 through IHI.

                If INFO > 0 and WANTZ is .TRUE., then on exit

                  (final value of Z(ILO:IHI,ILOZ:IHIZ)
                   =  (initial value of Z(ILO:IHI,ILOZ:IHIZ)*U

                where U is the unitary matrix in (*) (regard-
                less of the value of WANTT.)

                If INFO > 0 and WANTZ is .FALSE., then Z is not
                accessed.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Contributors:
Karen Braman and Ralph Byers, Department of Mathematics, University of Kansas, USA
References:
  K. Braman, R. Byers and R. Mathias, The Multi-Shift QR
  Algorithm Part I: Maintaining Well Focused Shifts, and Level 3
  Performance, SIAM Journal of Matrix Analysis, volume 23, pages
  929--947, 2002.

K. Braman, R. Byers and R. Mathias, The Multi-Shift QR Algorithm Part II: Aggressive Early Deflation, SIAM Journal of Matrix Analysis, volume 23, pages 948–973, 2002.

Definition at line 239 of file zlaqr0.f.

241 *
242 * -- LAPACK auxiliary routine --
243 * -- LAPACK is a software package provided by Univ. of Tennessee, --
244 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
245 *
246 * .. Scalar Arguments ..
247  INTEGER IHI, IHIZ, ILO, ILOZ, INFO, LDH, LDZ, LWORK, N
248  LOGICAL WANTT, WANTZ
249 * ..
250 * .. Array Arguments ..
251  COMPLEX*16 H( LDH, * ), W( * ), WORK( * ), Z( LDZ, * )
252 * ..
253 *
254 * ================================================================
255 *
256 * .. Parameters ..
257 *
258 * ==== Matrices of order NTINY or smaller must be processed by
259 * . ZLAHQR because of insufficient subdiagonal scratch space.
260 * . (This is a hard limit.) ====
261  INTEGER NTINY
262  parameter( ntiny = 15 )
263 *
264 * ==== Exceptional deflation windows: try to cure rare
265 * . slow convergence by varying the size of the
266 * . deflation window after KEXNW iterations. ====
267  INTEGER KEXNW
268  parameter( kexnw = 5 )
269 *
270 * ==== Exceptional shifts: try to cure rare slow convergence
271 * . with ad-hoc exceptional shifts every KEXSH iterations.
272 * . ====
273  INTEGER KEXSH
274  parameter( kexsh = 6 )
275 *
276 * ==== The constant WILK1 is used to form the exceptional
277 * . shifts. ====
278  DOUBLE PRECISION WILK1
279  parameter( wilk1 = 0.75d0 )
280  COMPLEX*16 ZERO, ONE
281  parameter( zero = ( 0.0d0, 0.0d0 ),
282  $ one = ( 1.0d0, 0.0d0 ) )
283  DOUBLE PRECISION TWO
284  parameter( two = 2.0d0 )
285 * ..
286 * .. Local Scalars ..
287  COMPLEX*16 AA, BB, CC, CDUM, DD, DET, RTDISC, SWAP, TR2
288  DOUBLE PRECISION S
289  INTEGER I, INF, IT, ITMAX, K, KACC22, KBOT, KDU, KS,
290  $ KT, KTOP, KU, KV, KWH, KWTOP, KWV, LD, LS,
291  $ LWKOPT, NDEC, NDFL, NH, NHO, NIBBLE, NMIN, NS,
292  $ NSMAX, NSR, NVE, NW, NWMAX, NWR, NWUPBD
293  LOGICAL SORTED
294  CHARACTER JBCMPZ*2
295 * ..
296 * .. External Functions ..
297  INTEGER ILAENV
298  EXTERNAL ilaenv
299 * ..
300 * .. Local Arrays ..
301  COMPLEX*16 ZDUM( 1, 1 )
302 * ..
303 * .. External Subroutines ..
304  EXTERNAL zlacpy, zlahqr, zlaqr3, zlaqr4, zlaqr5
305 * ..
306 * .. Intrinsic Functions ..
307  INTRINSIC abs, dble, dcmplx, dimag, int, max, min, mod,
308  $ sqrt
309 * ..
310 * .. Statement Functions ..
311  DOUBLE PRECISION CABS1
312 * ..
313 * .. Statement Function definitions ..
314  cabs1( cdum ) = abs( dble( cdum ) ) + abs( dimag( cdum ) )
315 * ..
316 * .. Executable Statements ..
317  info = 0
318 *
319 * ==== Quick return for N = 0: nothing to do. ====
320 *
321  IF( n.EQ.0 ) THEN
322  work( 1 ) = one
323  RETURN
324  END IF
325 *
326  IF( n.LE.ntiny ) THEN
327 *
328 * ==== Tiny matrices must use ZLAHQR. ====
329 *
330  lwkopt = 1
331  IF( lwork.NE.-1 )
332  $ CALL zlahqr( wantt, wantz, n, ilo, ihi, h, ldh, w, iloz,
333  $ ihiz, z, ldz, info )
334  ELSE
335 *
336 * ==== Use small bulge multi-shift QR with aggressive early
337 * . deflation on larger-than-tiny matrices. ====
338 *
339 * ==== Hope for the best. ====
340 *
341  info = 0
342 *
343 * ==== Set up job flags for ILAENV. ====
344 *
345  IF( wantt ) THEN
346  jbcmpz( 1: 1 ) = 'S'
347  ELSE
348  jbcmpz( 1: 1 ) = 'E'
349  END IF
350  IF( wantz ) THEN
351  jbcmpz( 2: 2 ) = 'V'
352  ELSE
353  jbcmpz( 2: 2 ) = 'N'
354  END IF
355 *
356 * ==== NWR = recommended deflation window size. At this
357 * . point, N .GT. NTINY = 15, so there is enough
358 * . subdiagonal workspace for NWR.GE.2 as required.
359 * . (In fact, there is enough subdiagonal space for
360 * . NWR.GE.4.) ====
361 *
362  nwr = ilaenv( 13, 'ZLAQR0', jbcmpz, n, ilo, ihi, lwork )
363  nwr = max( 2, nwr )
364  nwr = min( ihi-ilo+1, ( n-1 ) / 3, nwr )
365 *
366 * ==== NSR = recommended number of simultaneous shifts.
367 * . At this point N .GT. NTINY = 15, so there is at
368 * . enough subdiagonal workspace for NSR to be even
369 * . and greater than or equal to two as required. ====
370 *
371  nsr = ilaenv( 15, 'ZLAQR0', jbcmpz, n, ilo, ihi, lwork )
372  nsr = min( nsr, ( n-3 ) / 6, ihi-ilo )
373  nsr = max( 2, nsr-mod( nsr, 2 ) )
374 *
375 * ==== Estimate optimal workspace ====
376 *
377 * ==== Workspace query call to ZLAQR3 ====
378 *
379  CALL zlaqr3( wantt, wantz, n, ilo, ihi, nwr+1, h, ldh, iloz,
380  $ ihiz, z, ldz, ls, ld, w, h, ldh, n, h, ldh, n, h,
381  $ ldh, work, -1 )
382 *
383 * ==== Optimal workspace = MAX(ZLAQR5, ZLAQR3) ====
384 *
385  lwkopt = max( 3*nsr / 2, int( work( 1 ) ) )
386 *
387 * ==== Quick return in case of workspace query. ====
388 *
389  IF( lwork.EQ.-1 ) THEN
390  work( 1 ) = dcmplx( lwkopt, 0 )
391  RETURN
392  END IF
393 *
394 * ==== ZLAHQR/ZLAQR0 crossover point ====
395 *
396  nmin = ilaenv( 12, 'ZLAQR0', jbcmpz, n, ilo, ihi, lwork )
397  nmin = max( ntiny, nmin )
398 *
399 * ==== Nibble crossover point ====
400 *
401  nibble = ilaenv( 14, 'ZLAQR0', jbcmpz, n, ilo, ihi, lwork )
402  nibble = max( 0, nibble )
403 *
404 * ==== Accumulate reflections during ttswp? Use block
405 * . 2-by-2 structure during matrix-matrix multiply? ====
406 *
407  kacc22 = ilaenv( 16, 'ZLAQR0', jbcmpz, n, ilo, ihi, lwork )
408  kacc22 = max( 0, kacc22 )
409  kacc22 = min( 2, kacc22 )
410 *
411 * ==== NWMAX = the largest possible deflation window for
412 * . which there is sufficient workspace. ====
413 *
414  nwmax = min( ( n-1 ) / 3, lwork / 2 )
415  nw = nwmax
416 *
417 * ==== NSMAX = the Largest number of simultaneous shifts
418 * . for which there is sufficient workspace. ====
419 *
420  nsmax = min( ( n-3 ) / 6, 2*lwork / 3 )
421  nsmax = nsmax - mod( nsmax, 2 )
422 *
423 * ==== NDFL: an iteration count restarted at deflation. ====
424 *
425  ndfl = 1
426 *
427 * ==== ITMAX = iteration limit ====
428 *
429  itmax = max( 30, 2*kexsh )*max( 10, ( ihi-ilo+1 ) )
430 *
431 * ==== Last row and column in the active block ====
432 *
433  kbot = ihi
434 *
435 * ==== Main Loop ====
436 *
437  DO 70 it = 1, itmax
438 *
439 * ==== Done when KBOT falls below ILO ====
440 *
441  IF( kbot.LT.ilo )
442  $ GO TO 80
443 *
444 * ==== Locate active block ====
445 *
446  DO 10 k = kbot, ilo + 1, -1
447  IF( h( k, k-1 ).EQ.zero )
448  $ GO TO 20
449  10 CONTINUE
450  k = ilo
451  20 CONTINUE
452  ktop = k
453 *
454 * ==== Select deflation window size:
455 * . Typical Case:
456 * . If possible and advisable, nibble the entire
457 * . active block. If not, use size MIN(NWR,NWMAX)
458 * . or MIN(NWR+1,NWMAX) depending upon which has
459 * . the smaller corresponding subdiagonal entry
460 * . (a heuristic).
461 * .
462 * . Exceptional Case:
463 * . If there have been no deflations in KEXNW or
464 * . more iterations, then vary the deflation window
465 * . size. At first, because, larger windows are,
466 * . in general, more powerful than smaller ones,
467 * . rapidly increase the window to the maximum possible.
468 * . Then, gradually reduce the window size. ====
469 *
470  nh = kbot - ktop + 1
471  nwupbd = min( nh, nwmax )
472  IF( ndfl.LT.kexnw ) THEN
473  nw = min( nwupbd, nwr )
474  ELSE
475  nw = min( nwupbd, 2*nw )
476  END IF
477  IF( nw.LT.nwmax ) THEN
478  IF( nw.GE.nh-1 ) THEN
479  nw = nh
480  ELSE
481  kwtop = kbot - nw + 1
482  IF( cabs1( h( kwtop, kwtop-1 ) ).GT.
483  $ cabs1( h( kwtop-1, kwtop-2 ) ) )nw = nw + 1
484  END IF
485  END IF
486  IF( ndfl.LT.kexnw ) THEN
487  ndec = -1
488  ELSE IF( ndec.GE.0 .OR. nw.GE.nwupbd ) THEN
489  ndec = ndec + 1
490  IF( nw-ndec.LT.2 )
491  $ ndec = 0
492  nw = nw - ndec
493  END IF
494 *
495 * ==== Aggressive early deflation:
496 * . split workspace under the subdiagonal into
497 * . - an nw-by-nw work array V in the lower
498 * . left-hand-corner,
499 * . - an NW-by-at-least-NW-but-more-is-better
500 * . (NW-by-NHO) horizontal work array along
501 * . the bottom edge,
502 * . - an at-least-NW-but-more-is-better (NHV-by-NW)
503 * . vertical work array along the left-hand-edge.
504 * . ====
505 *
506  kv = n - nw + 1
507  kt = nw + 1
508  nho = ( n-nw-1 ) - kt + 1
509  kwv = nw + 2
510  nve = ( n-nw ) - kwv + 1
511 *
512 * ==== Aggressive early deflation ====
513 *
514  CALL zlaqr3( wantt, wantz, n, ktop, kbot, nw, h, ldh, iloz,
515  $ ihiz, z, ldz, ls, ld, w, h( kv, 1 ), ldh, nho,
516  $ h( kv, kt ), ldh, nve, h( kwv, 1 ), ldh, work,
517  $ lwork )
518 *
519 * ==== Adjust KBOT accounting for new deflations. ====
520 *
521  kbot = kbot - ld
522 *
523 * ==== KS points to the shifts. ====
524 *
525  ks = kbot - ls + 1
526 *
527 * ==== Skip an expensive QR sweep if there is a (partly
528 * . heuristic) reason to expect that many eigenvalues
529 * . will deflate without it. Here, the QR sweep is
530 * . skipped if many eigenvalues have just been deflated
531 * . or if the remaining active block is small.
532 *
533  IF( ( ld.EQ.0 ) .OR. ( ( 100*ld.LE.nw*nibble ) .AND. ( kbot-
534  $ ktop+1.GT.min( nmin, nwmax ) ) ) ) THEN
535 *
536 * ==== NS = nominal number of simultaneous shifts.
537 * . This may be lowered (slightly) if ZLAQR3
538 * . did not provide that many shifts. ====
539 *
540  ns = min( nsmax, nsr, max( 2, kbot-ktop ) )
541  ns = ns - mod( ns, 2 )
542 *
543 * ==== If there have been no deflations
544 * . in a multiple of KEXSH iterations,
545 * . then try exceptional shifts.
546 * . Otherwise use shifts provided by
547 * . ZLAQR3 above or from the eigenvalues
548 * . of a trailing principal submatrix. ====
549 *
550  IF( mod( ndfl, kexsh ).EQ.0 ) THEN
551  ks = kbot - ns + 1
552  DO 30 i = kbot, ks + 1, -2
553  w( i ) = h( i, i ) + wilk1*cabs1( h( i, i-1 ) )
554  w( i-1 ) = w( i )
555  30 CONTINUE
556  ELSE
557 *
558 * ==== Got NS/2 or fewer shifts? Use ZLAQR4 or
559 * . ZLAHQR on a trailing principal submatrix to
560 * . get more. (Since NS.LE.NSMAX.LE.(N+6)/9,
561 * . there is enough space below the subdiagonal
562 * . to fit an NS-by-NS scratch array.) ====
563 *
564  IF( kbot-ks+1.LE.ns / 2 ) THEN
565  ks = kbot - ns + 1
566  kt = n - ns + 1
567  CALL zlacpy( 'A', ns, ns, h( ks, ks ), ldh,
568  $ h( kt, 1 ), ldh )
569  IF( ns.GT.nmin ) THEN
570  CALL zlaqr4( .false., .false., ns, 1, ns,
571  $ h( kt, 1 ), ldh, w( ks ), 1, 1,
572  $ zdum, 1, work, lwork, inf )
573  ELSE
574  CALL zlahqr( .false., .false., ns, 1, ns,
575  $ h( kt, 1 ), ldh, w( ks ), 1, 1,
576  $ zdum, 1, inf )
577  END IF
578  ks = ks + inf
579 *
580 * ==== In case of a rare QR failure use
581 * . eigenvalues of the trailing 2-by-2
582 * . principal submatrix. Scale to avoid
583 * . overflows, underflows and subnormals.
584 * . (The scale factor S can not be zero,
585 * . because H(KBOT,KBOT-1) is nonzero.) ====
586 *
587  IF( ks.GE.kbot ) THEN
588  s = cabs1( h( kbot-1, kbot-1 ) ) +
589  $ cabs1( h( kbot, kbot-1 ) ) +
590  $ cabs1( h( kbot-1, kbot ) ) +
591  $ cabs1( h( kbot, kbot ) )
592  aa = h( kbot-1, kbot-1 ) / s
593  cc = h( kbot, kbot-1 ) / s
594  bb = h( kbot-1, kbot ) / s
595  dd = h( kbot, kbot ) / s
596  tr2 = ( aa+dd ) / two
597  det = ( aa-tr2 )*( dd-tr2 ) - bb*cc
598  rtdisc = sqrt( -det )
599  w( kbot-1 ) = ( tr2+rtdisc )*s
600  w( kbot ) = ( tr2-rtdisc )*s
601 *
602  ks = kbot - 1
603  END IF
604  END IF
605 *
606  IF( kbot-ks+1.GT.ns ) THEN
607 *
608 * ==== Sort the shifts (Helps a little) ====
609 *
610  sorted = .false.
611  DO 50 k = kbot, ks + 1, -1
612  IF( sorted )
613  $ GO TO 60
614  sorted = .true.
615  DO 40 i = ks, k - 1
616  IF( cabs1( w( i ) ).LT.cabs1( w( i+1 ) ) )
617  $ THEN
618  sorted = .false.
619  swap = w( i )
620  w( i ) = w( i+1 )
621  w( i+1 ) = swap
622  END IF
623  40 CONTINUE
624  50 CONTINUE
625  60 CONTINUE
626  END IF
627  END IF
628 *
629 * ==== If there are only two shifts, then use
630 * . only one. ====
631 *
632  IF( kbot-ks+1.EQ.2 ) THEN
633  IF( cabs1( w( kbot )-h( kbot, kbot ) ).LT.
634  $ cabs1( w( kbot-1 )-h( kbot, kbot ) ) ) THEN
635  w( kbot-1 ) = w( kbot )
636  ELSE
637  w( kbot ) = w( kbot-1 )
638  END IF
639  END IF
640 *
641 * ==== Use up to NS of the the smallest magnitude
642 * . shifts. If there aren't NS shifts available,
643 * . then use them all, possibly dropping one to
644 * . make the number of shifts even. ====
645 *
646  ns = min( ns, kbot-ks+1 )
647  ns = ns - mod( ns, 2 )
648  ks = kbot - ns + 1
649 *
650 * ==== Small-bulge multi-shift QR sweep:
651 * . split workspace under the subdiagonal into
652 * . - a KDU-by-KDU work array U in the lower
653 * . left-hand-corner,
654 * . - a KDU-by-at-least-KDU-but-more-is-better
655 * . (KDU-by-NHo) horizontal work array WH along
656 * . the bottom edge,
657 * . - and an at-least-KDU-but-more-is-better-by-KDU
658 * . (NVE-by-KDU) vertical work WV arrow along
659 * . the left-hand-edge. ====
660 *
661  kdu = 2*ns
662  ku = n - kdu + 1
663  kwh = kdu + 1
664  nho = ( n-kdu+1-4 ) - ( kdu+1 ) + 1
665  kwv = kdu + 4
666  nve = n - kdu - kwv + 1
667 *
668 * ==== Small-bulge multi-shift QR sweep ====
669 *
670  CALL zlaqr5( wantt, wantz, kacc22, n, ktop, kbot, ns,
671  $ w( ks ), h, ldh, iloz, ihiz, z, ldz, work,
672  $ 3, h( ku, 1 ), ldh, nve, h( kwv, 1 ), ldh,
673  $ nho, h( ku, kwh ), ldh )
674  END IF
675 *
676 * ==== Note progress (or the lack of it). ====
677 *
678  IF( ld.GT.0 ) THEN
679  ndfl = 1
680  ELSE
681  ndfl = ndfl + 1
682  END IF
683 *
684 * ==== End of main loop ====
685  70 CONTINUE
686 *
687 * ==== Iteration limit exceeded. Set INFO to show where
688 * . the problem occurred and exit. ====
689 *
690  info = kbot
691  80 CONTINUE
692  END IF
693 *
694 * ==== Return the optimal value of LWORK. ====
695 *
696  work( 1 ) = dcmplx( lwkopt, 0 )
697 *
698 * ==== End of ZLAQR0 ====
699 *
integer function ilaenv(ISPEC, NAME, OPTS, N1, N2, N3, N4)
ILAENV
Definition: ilaenv.f:162
subroutine zlaqr5(WANTT, WANTZ, KACC22, N, KTOP, KBOT, NSHFTS, S, H, LDH, ILOZ, IHIZ, Z, LDZ, V, LDV, U, LDU, NV, WV, LDWV, NH, WH, LDWH)
ZLAQR5 performs a single small-bulge multi-shift QR sweep.
Definition: zlaqr5.f:257
subroutine zlahqr(WANTT, WANTZ, N, ILO, IHI, H, LDH, W, ILOZ, IHIZ, Z, LDZ, INFO)
ZLAHQR computes the eigenvalues and Schur factorization of an upper Hessenberg matrix,...
Definition: zlahqr.f:195
subroutine zlacpy(UPLO, M, N, A, LDA, B, LDB)
ZLACPY copies all or part of one two-dimensional array to another.
Definition: zlacpy.f:103
subroutine zlaqr3(WANTT, WANTZ, N, KTOP, KBOT, NW, H, LDH, ILOZ, IHIZ, Z, LDZ, NS, ND, SH, V, LDV, NH, T, LDT, NV, WV, LDWV, WORK, LWORK)
ZLAQR3 performs the unitary similarity transformation of a Hessenberg matrix to detect and deflate fu...
Definition: zlaqr3.f:267
subroutine zlaqr4(WANTT, WANTZ, N, ILO, IHI, H, LDH, W, ILOZ, IHIZ, Z, LDZ, WORK, LWORK, INFO)
ZLAQR4 computes the eigenvalues of a Hessenberg matrix, and optionally the matrices from the Schur de...
Definition: zlaqr4.f:247
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