LAPACK  3.8.0
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 .GE. 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.GT.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.GT.0, then 1.LE.ILO.LE.IHI.LE.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.GT.0 is given under the
           description of INFO below.)

           This subroutine may explicitly set H(i,j) = 0 for i.GT.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 .GE. 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 .LE. ILOZ .LE. ILO; IHI .LE. IHIZ .LE. 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.GT.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.GE.MAX(1,IHIZ).  Otherwize, LDZ.GE.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 .GE. 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
           .GT. 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 .GT. 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 .GT. 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 .GT. 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 .GT. 0 and WANTZ is .FALSE., then Z is not
                accessed.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
December 2016
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 243 of file zlaqr0.f.

243 *
244 * -- LAPACK auxiliary routine (version 3.7.0) --
245 * -- LAPACK is a software package provided by Univ. of Tennessee, --
246 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
247 * December 2016
248 *
249 * .. Scalar Arguments ..
250  INTEGER ihi, ihiz, ilo, iloz, info, ldh, ldz, lwork, n
251  LOGICAL wantt, wantz
252 * ..
253 * .. Array Arguments ..
254  COMPLEX*16 h( ldh, * ), w( * ), work( * ), z( ldz, * )
255 * ..
256 *
257 * ================================================================
258 *
259 * .. Parameters ..
260 *
261 * ==== Matrices of order NTINY or smaller must be processed by
262 * . ZLAHQR because of insufficient subdiagonal scratch space.
263 * . (This is a hard limit.) ====
264  INTEGER ntiny
265  parameter( ntiny = 11 )
266 *
267 * ==== Exceptional deflation windows: try to cure rare
268 * . slow convergence by varying the size of the
269 * . deflation window after KEXNW iterations. ====
270  INTEGER kexnw
271  parameter( kexnw = 5 )
272 *
273 * ==== Exceptional shifts: try to cure rare slow convergence
274 * . with ad-hoc exceptional shifts every KEXSH iterations.
275 * . ====
276  INTEGER kexsh
277  parameter( kexsh = 6 )
278 *
279 * ==== The constant WILK1 is used to form the exceptional
280 * . shifts. ====
281  DOUBLE PRECISION wilk1
282  parameter( wilk1 = 0.75d0 )
283  COMPLEX*16 zero, one
284  parameter( zero = ( 0.0d0, 0.0d0 ),
285  $ one = ( 1.0d0, 0.0d0 ) )
286  DOUBLE PRECISION two
287  parameter( two = 2.0d0 )
288 * ..
289 * .. Local Scalars ..
290  COMPLEX*16 aa, bb, cc, cdum, dd, det, rtdisc, swap, tr2
291  DOUBLE PRECISION s
292  INTEGER i, inf, it, itmax, k, kacc22, kbot, kdu, ks,
293  $ kt, ktop, ku, kv, kwh, kwtop, kwv, ld, ls,
294  $ lwkopt, ndec, ndfl, nh, nho, nibble, nmin, ns,
295  $ nsmax, nsr, nve, nw, nwmax, nwr, nwupbd
296  LOGICAL sorted
297  CHARACTER jbcmpz*2
298 * ..
299 * .. External Functions ..
300  INTEGER ilaenv
301  EXTERNAL ilaenv
302 * ..
303 * .. Local Arrays ..
304  COMPLEX*16 zdum( 1, 1 )
305 * ..
306 * .. External Subroutines ..
307  EXTERNAL zlacpy, zlahqr, zlaqr3, zlaqr4, zlaqr5
308 * ..
309 * .. Intrinsic Functions ..
310  INTRINSIC abs, dble, dcmplx, dimag, int, max, min, mod,
311  $ sqrt
312 * ..
313 * .. Statement Functions ..
314  DOUBLE PRECISION cabs1
315 * ..
316 * .. Statement Function definitions ..
317  cabs1( cdum ) = abs( dble( cdum ) ) + abs( dimag( cdum ) )
318 * ..
319 * .. Executable Statements ..
320  info = 0
321 *
322 * ==== Quick return for N = 0: nothing to do. ====
323 *
324  IF( n.EQ.0 ) THEN
325  work( 1 ) = one
326  RETURN
327  END IF
328 *
329  IF( n.LE.ntiny ) THEN
330 *
331 * ==== Tiny matrices must use ZLAHQR. ====
332 *
333  lwkopt = 1
334  IF( lwork.NE.-1 )
335  $ CALL zlahqr( wantt, wantz, n, ilo, ihi, h, ldh, w, iloz,
336  $ ihiz, z, ldz, info )
337  ELSE
338 *
339 * ==== Use small bulge multi-shift QR with aggressive early
340 * . deflation on larger-than-tiny matrices. ====
341 *
342 * ==== Hope for the best. ====
343 *
344  info = 0
345 *
346 * ==== Set up job flags for ILAENV. ====
347 *
348  IF( wantt ) THEN
349  jbcmpz( 1: 1 ) = 'S'
350  ELSE
351  jbcmpz( 1: 1 ) = 'E'
352  END IF
353  IF( wantz ) THEN
354  jbcmpz( 2: 2 ) = 'V'
355  ELSE
356  jbcmpz( 2: 2 ) = 'N'
357  END IF
358 *
359 * ==== NWR = recommended deflation window size. At this
360 * . point, N .GT. NTINY = 11, so there is enough
361 * . subdiagonal workspace for NWR.GE.2 as required.
362 * . (In fact, there is enough subdiagonal space for
363 * . NWR.GE.3.) ====
364 *
365  nwr = ilaenv( 13, 'ZLAQR0', jbcmpz, n, ilo, ihi, lwork )
366  nwr = max( 2, nwr )
367  nwr = min( ihi-ilo+1, ( n-1 ) / 3, nwr )
368 *
369 * ==== NSR = recommended number of simultaneous shifts.
370 * . At this point N .GT. NTINY = 11, so there is at
371 * . enough subdiagonal workspace for NSR to be even
372 * . and greater than or equal to two as required. ====
373 *
374  nsr = ilaenv( 15, 'ZLAQR0', jbcmpz, n, ilo, ihi, lwork )
375  nsr = min( nsr, ( n+6 ) / 9, ihi-ilo )
376  nsr = max( 2, nsr-mod( nsr, 2 ) )
377 *
378 * ==== Estimate optimal workspace ====
379 *
380 * ==== Workspace query call to ZLAQR3 ====
381 *
382  CALL zlaqr3( wantt, wantz, n, ilo, ihi, nwr+1, h, ldh, iloz,
383  $ ihiz, z, ldz, ls, ld, w, h, ldh, n, h, ldh, n, h,
384  $ ldh, work, -1 )
385 *
386 * ==== Optimal workspace = MAX(ZLAQR5, ZLAQR3) ====
387 *
388  lwkopt = max( 3*nsr / 2, int( work( 1 ) ) )
389 *
390 * ==== Quick return in case of workspace query. ====
391 *
392  IF( lwork.EQ.-1 ) THEN
393  work( 1 ) = dcmplx( lwkopt, 0 )
394  RETURN
395  END IF
396 *
397 * ==== ZLAHQR/ZLAQR0 crossover point ====
398 *
399  nmin = ilaenv( 12, 'ZLAQR0', jbcmpz, n, ilo, ihi, lwork )
400  nmin = max( ntiny, nmin )
401 *
402 * ==== Nibble crossover point ====
403 *
404  nibble = ilaenv( 14, 'ZLAQR0', jbcmpz, n, ilo, ihi, lwork )
405  nibble = max( 0, nibble )
406 *
407 * ==== Accumulate reflections during ttswp? Use block
408 * . 2-by-2 structure during matrix-matrix multiply? ====
409 *
410  kacc22 = ilaenv( 16, 'ZLAQR0', jbcmpz, n, ilo, ihi, lwork )
411  kacc22 = max( 0, kacc22 )
412  kacc22 = min( 2, kacc22 )
413 *
414 * ==== NWMAX = the largest possible deflation window for
415 * . which there is sufficient workspace. ====
416 *
417  nwmax = min( ( n-1 ) / 3, lwork / 2 )
418  nw = nwmax
419 *
420 * ==== NSMAX = the Largest number of simultaneous shifts
421 * . for which there is sufficient workspace. ====
422 *
423  nsmax = min( ( n+6 ) / 9, 2*lwork / 3 )
424  nsmax = nsmax - mod( nsmax, 2 )
425 *
426 * ==== NDFL: an iteration count restarted at deflation. ====
427 *
428  ndfl = 1
429 *
430 * ==== ITMAX = iteration limit ====
431 *
432  itmax = max( 30, 2*kexsh )*max( 10, ( ihi-ilo+1 ) )
433 *
434 * ==== Last row and column in the active block ====
435 *
436  kbot = ihi
437 *
438 * ==== Main Loop ====
439 *
440  DO 70 it = 1, itmax
441 *
442 * ==== Done when KBOT falls below ILO ====
443 *
444  IF( kbot.LT.ilo )
445  $ GO TO 80
446 *
447 * ==== Locate active block ====
448 *
449  DO 10 k = kbot, ilo + 1, -1
450  IF( h( k, k-1 ).EQ.zero )
451  $ GO TO 20
452  10 CONTINUE
453  k = ilo
454  20 CONTINUE
455  ktop = k
456 *
457 * ==== Select deflation window size:
458 * . Typical Case:
459 * . If possible and advisable, nibble the entire
460 * . active block. If not, use size MIN(NWR,NWMAX)
461 * . or MIN(NWR+1,NWMAX) depending upon which has
462 * . the smaller corresponding subdiagonal entry
463 * . (a heuristic).
464 * .
465 * . Exceptional Case:
466 * . If there have been no deflations in KEXNW or
467 * . more iterations, then vary the deflation window
468 * . size. At first, because, larger windows are,
469 * . in general, more powerful than smaller ones,
470 * . rapidly increase the window to the maximum possible.
471 * . Then, gradually reduce the window size. ====
472 *
473  nh = kbot - ktop + 1
474  nwupbd = min( nh, nwmax )
475  IF( ndfl.LT.kexnw ) THEN
476  nw = min( nwupbd, nwr )
477  ELSE
478  nw = min( nwupbd, 2*nw )
479  END IF
480  IF( nw.LT.nwmax ) THEN
481  IF( nw.GE.nh-1 ) THEN
482  nw = nh
483  ELSE
484  kwtop = kbot - nw + 1
485  IF( cabs1( h( kwtop, kwtop-1 ) ).GT.
486  $ cabs1( h( kwtop-1, kwtop-2 ) ) )nw = nw + 1
487  END IF
488  END IF
489  IF( ndfl.LT.kexnw ) THEN
490  ndec = -1
491  ELSE IF( ndec.GE.0 .OR. nw.GE.nwupbd ) THEN
492  ndec = ndec + 1
493  IF( nw-ndec.LT.2 )
494  $ ndec = 0
495  nw = nw - ndec
496  END IF
497 *
498 * ==== Aggressive early deflation:
499 * . split workspace under the subdiagonal into
500 * . - an nw-by-nw work array V in the lower
501 * . left-hand-corner,
502 * . - an NW-by-at-least-NW-but-more-is-better
503 * . (NW-by-NHO) horizontal work array along
504 * . the bottom edge,
505 * . - an at-least-NW-but-more-is-better (NHV-by-NW)
506 * . vertical work array along the left-hand-edge.
507 * . ====
508 *
509  kv = n - nw + 1
510  kt = nw + 1
511  nho = ( n-nw-1 ) - kt + 1
512  kwv = nw + 2
513  nve = ( n-nw ) - kwv + 1
514 *
515 * ==== Aggressive early deflation ====
516 *
517  CALL zlaqr3( wantt, wantz, n, ktop, kbot, nw, h, ldh, iloz,
518  $ ihiz, z, ldz, ls, ld, w, h( kv, 1 ), ldh, nho,
519  $ h( kv, kt ), ldh, nve, h( kwv, 1 ), ldh, work,
520  $ lwork )
521 *
522 * ==== Adjust KBOT accounting for new deflations. ====
523 *
524  kbot = kbot - ld
525 *
526 * ==== KS points to the shifts. ====
527 *
528  ks = kbot - ls + 1
529 *
530 * ==== Skip an expensive QR sweep if there is a (partly
531 * . heuristic) reason to expect that many eigenvalues
532 * . will deflate without it. Here, the QR sweep is
533 * . skipped if many eigenvalues have just been deflated
534 * . or if the remaining active block is small.
535 *
536  IF( ( ld.EQ.0 ) .OR. ( ( 100*ld.LE.nw*nibble ) .AND. ( kbot-
537  $ ktop+1.GT.min( nmin, nwmax ) ) ) ) THEN
538 *
539 * ==== NS = nominal number of simultaneous shifts.
540 * . This may be lowered (slightly) if ZLAQR3
541 * . did not provide that many shifts. ====
542 *
543  ns = min( nsmax, nsr, max( 2, kbot-ktop ) )
544  ns = ns - mod( ns, 2 )
545 *
546 * ==== If there have been no deflations
547 * . in a multiple of KEXSH iterations,
548 * . then try exceptional shifts.
549 * . Otherwise use shifts provided by
550 * . ZLAQR3 above or from the eigenvalues
551 * . of a trailing principal submatrix. ====
552 *
553  IF( mod( ndfl, kexsh ).EQ.0 ) THEN
554  ks = kbot - ns + 1
555  DO 30 i = kbot, ks + 1, -2
556  w( i ) = h( i, i ) + wilk1*cabs1( h( i, i-1 ) )
557  w( i-1 ) = w( i )
558  30 CONTINUE
559  ELSE
560 *
561 * ==== Got NS/2 or fewer shifts? Use ZLAQR4 or
562 * . ZLAHQR on a trailing principal submatrix to
563 * . get more. (Since NS.LE.NSMAX.LE.(N+6)/9,
564 * . there is enough space below the subdiagonal
565 * . to fit an NS-by-NS scratch array.) ====
566 *
567  IF( kbot-ks+1.LE.ns / 2 ) THEN
568  ks = kbot - ns + 1
569  kt = n - ns + 1
570  CALL zlacpy( 'A', ns, ns, h( ks, ks ), ldh,
571  $ h( kt, 1 ), ldh )
572  IF( ns.GT.nmin ) THEN
573  CALL zlaqr4( .false., .false., ns, 1, ns,
574  $ h( kt, 1 ), ldh, w( ks ), 1, 1,
575  $ zdum, 1, work, lwork, inf )
576  ELSE
577  CALL zlahqr( .false., .false., ns, 1, ns,
578  $ h( kt, 1 ), ldh, w( ks ), 1, 1,
579  $ zdum, 1, inf )
580  END IF
581  ks = ks + inf
582 *
583 * ==== In case of a rare QR failure use
584 * . eigenvalues of the trailing 2-by-2
585 * . principal submatrix. Scale to avoid
586 * . overflows, underflows and subnormals.
587 * . (The scale factor S can not be zero,
588 * . because H(KBOT,KBOT-1) is nonzero.) ====
589 *
590  IF( ks.GE.kbot ) THEN
591  s = cabs1( h( kbot-1, kbot-1 ) ) +
592  $ cabs1( h( kbot, kbot-1 ) ) +
593  $ cabs1( h( kbot-1, kbot ) ) +
594  $ cabs1( h( kbot, kbot ) )
595  aa = h( kbot-1, kbot-1 ) / s
596  cc = h( kbot, kbot-1 ) / s
597  bb = h( kbot-1, kbot ) / s
598  dd = h( kbot, kbot ) / s
599  tr2 = ( aa+dd ) / two
600  det = ( aa-tr2 )*( dd-tr2 ) - bb*cc
601  rtdisc = sqrt( -det )
602  w( kbot-1 ) = ( tr2+rtdisc )*s
603  w( kbot ) = ( tr2-rtdisc )*s
604 *
605  ks = kbot - 1
606  END IF
607  END IF
608 *
609  IF( kbot-ks+1.GT.ns ) THEN
610 *
611 * ==== Sort the shifts (Helps a little) ====
612 *
613  sorted = .false.
614  DO 50 k = kbot, ks + 1, -1
615  IF( sorted )
616  $ GO TO 60
617  sorted = .true.
618  DO 40 i = ks, k - 1
619  IF( cabs1( w( i ) ).LT.cabs1( w( i+1 ) ) )
620  $ THEN
621  sorted = .false.
622  swap = w( i )
623  w( i ) = w( i+1 )
624  w( i+1 ) = swap
625  END IF
626  40 CONTINUE
627  50 CONTINUE
628  60 CONTINUE
629  END IF
630  END IF
631 *
632 * ==== If there are only two shifts, then use
633 * . only one. ====
634 *
635  IF( kbot-ks+1.EQ.2 ) THEN
636  IF( cabs1( w( kbot )-h( kbot, kbot ) ).LT.
637  $ cabs1( w( kbot-1 )-h( kbot, kbot ) ) ) THEN
638  w( kbot-1 ) = w( kbot )
639  ELSE
640  w( kbot ) = w( kbot-1 )
641  END IF
642  END IF
643 *
644 * ==== Use up to NS of the the smallest magnatiude
645 * . shifts. If there aren't NS shifts available,
646 * . then use them all, possibly dropping one to
647 * . make the number of shifts even. ====
648 *
649  ns = min( ns, kbot-ks+1 )
650  ns = ns - mod( ns, 2 )
651  ks = kbot - ns + 1
652 *
653 * ==== Small-bulge multi-shift QR sweep:
654 * . split workspace under the subdiagonal into
655 * . - a KDU-by-KDU work array U in the lower
656 * . left-hand-corner,
657 * . - a KDU-by-at-least-KDU-but-more-is-better
658 * . (KDU-by-NHo) horizontal work array WH along
659 * . the bottom edge,
660 * . - and an at-least-KDU-but-more-is-better-by-KDU
661 * . (NVE-by-KDU) vertical work WV arrow along
662 * . the left-hand-edge. ====
663 *
664  kdu = 3*ns - 3
665  ku = n - kdu + 1
666  kwh = kdu + 1
667  nho = ( n-kdu+1-4 ) - ( kdu+1 ) + 1
668  kwv = kdu + 4
669  nve = n - kdu - kwv + 1
670 *
671 * ==== Small-bulge multi-shift QR sweep ====
672 *
673  CALL zlaqr5( wantt, wantz, kacc22, n, ktop, kbot, ns,
674  $ w( ks ), h, ldh, iloz, ihiz, z, ldz, work,
675  $ 3, h( ku, 1 ), ldh, nve, h( kwv, 1 ), ldh,
676  $ nho, h( ku, kwh ), ldh )
677  END IF
678 *
679 * ==== Note progress (or the lack of it). ====
680 *
681  IF( ld.GT.0 ) THEN
682  ndfl = 1
683  ELSE
684  ndfl = ndfl + 1
685  END IF
686 *
687 * ==== End of main loop ====
688  70 CONTINUE
689 *
690 * ==== Iteration limit exceeded. Set INFO to show where
691 * . the problem occurred and exit. ====
692 *
693  info = kbot
694  80 CONTINUE
695  END IF
696 *
697 * ==== Return the optimal value of LWORK. ====
698 *
699  work( 1 ) = dcmplx( lwkopt, 0 )
700 *
701 * ==== End of ZLAQR0 ====
702 *
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:269
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, using the double-shift/single-shift QR algorithm.
Definition: zlahqr.f:197
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 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:251
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:249
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