LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
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◆ zlaqr3()

subroutine zlaqr3 ( logical  WANTT,
logical  WANTZ,
integer  N,
integer  KTOP,
integer  KBOT,
integer  NW,
complex*16, dimension( ldh, * )  H,
integer  LDH,
integer  ILOZ,
integer  IHIZ,
complex*16, dimension( ldz, * )  Z,
integer  LDZ,
integer  NS,
integer  ND,
complex*16, dimension( * )  SH,
complex*16, dimension( ldv, * )  V,
integer  LDV,
integer  NH,
complex*16, dimension( ldt, * )  T,
integer  LDT,
integer  NV,
complex*16, dimension( ldwv, * )  WV,
integer  LDWV,
complex*16, dimension( * )  WORK,
integer  LWORK 
)

ZLAQR3 performs the unitary similarity transformation of a Hessenberg matrix to detect and deflate fully converged eigenvalues from a trailing principal submatrix (aggressive early deflation).

Download ZLAQR3 + dependencies [TGZ] [ZIP] [TXT]

Purpose:
    Aggressive early deflation:

    ZLAQR3 accepts as input an upper Hessenberg matrix
    H and performs an unitary similarity transformation
    designed to detect and deflate fully converged eigenvalues from
    a trailing principal submatrix.  On output H has been over-
    written by a new Hessenberg matrix that is a perturbation of
    an unitary similarity transformation of H.  It is to be
    hoped that the final version of H has many zero subdiagonal
    entries.
Parameters
[in]WANTT
          WANTT is LOGICAL
          If .TRUE., then the Hessenberg matrix H is fully updated
          so that the triangular Schur factor may be
          computed (in cooperation with the calling subroutine).
          If .FALSE., then only enough of H is updated to preserve
          the eigenvalues.
[in]WANTZ
          WANTZ is LOGICAL
          If .TRUE., then the unitary matrix Z is updated so
          so that the unitary Schur factor may be computed
          (in cooperation with the calling subroutine).
          If .FALSE., then Z is not referenced.
[in]N
          N is INTEGER
          The order of the matrix H and (if WANTZ is .TRUE.) the
          order of the unitary matrix Z.
[in]KTOP
          KTOP is INTEGER
          It is assumed that either KTOP = 1 or H(KTOP,KTOP-1)=0.
          KBOT and KTOP together determine an isolated block
          along the diagonal of the Hessenberg matrix.
[in]KBOT
          KBOT is INTEGER
          It is assumed without a check that either
          KBOT = N or H(KBOT+1,KBOT)=0.  KBOT and KTOP together
          determine an isolated block along the diagonal of the
          Hessenberg matrix.
[in]NW
          NW is INTEGER
          Deflation window size.  1 <= NW <= (KBOT-KTOP+1).
[in,out]H
          H is COMPLEX*16 array, dimension (LDH,N)
          On input the initial N-by-N section of H stores the
          Hessenberg matrix undergoing aggressive early deflation.
          On output H has been transformed by a unitary
          similarity transformation, perturbed, and the returned
          to Hessenberg form that (it is to be hoped) has some
          zero subdiagonal entries.
[in]LDH
          LDH is INTEGER
          Leading dimension of H just as declared in the calling
          subroutine.  N <= LDH
[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 <= IHIZ <= N.
[in,out]Z
          Z is COMPLEX*16 array, dimension (LDZ,N)
          IF WANTZ is .TRUE., then on output, the unitary
          similarity transformation mentioned above has been
          accumulated into Z(ILOZ:IHIZ,ILOZ:IHIZ) from the right.
          If WANTZ is .FALSE., then Z is unreferenced.
[in]LDZ
          LDZ is INTEGER
          The leading dimension of Z just as declared in the
          calling subroutine.  1 <= LDZ.
[out]NS
          NS is INTEGER
          The number of unconverged (ie approximate) eigenvalues
          returned in SR and SI that may be used as shifts by the
          calling subroutine.
[out]ND
          ND is INTEGER
          The number of converged eigenvalues uncovered by this
          subroutine.
[out]SH
          SH is COMPLEX*16 array, dimension (KBOT)
          On output, approximate eigenvalues that may
          be used for shifts are stored in SH(KBOT-ND-NS+1)
          through SR(KBOT-ND).  Converged eigenvalues are
          stored in SH(KBOT-ND+1) through SH(KBOT).
[out]V
          V is COMPLEX*16 array, dimension (LDV,NW)
          An NW-by-NW work array.
[in]LDV
          LDV is INTEGER
          The leading dimension of V just as declared in the
          calling subroutine.  NW <= LDV
[in]NH
          NH is INTEGER
          The number of columns of T.  NH >= NW.
[out]T
          T is COMPLEX*16 array, dimension (LDT,NW)
[in]LDT
          LDT is INTEGER
          The leading dimension of T just as declared in the
          calling subroutine.  NW <= LDT
[in]NV
          NV is INTEGER
          The number of rows of work array WV available for
          workspace.  NV >= NW.
[out]WV
          WV is COMPLEX*16 array, dimension (LDWV,NW)
[in]LDWV
          LDWV is INTEGER
          The leading dimension of W just as declared in the
          calling subroutine.  NW <= LDV
[out]WORK
          WORK is COMPLEX*16 array, dimension (LWORK)
          On exit, WORK(1) is set to an estimate of the optimal value
          of LWORK for the given values of N, NW, KTOP and KBOT.
[in]LWORK
          LWORK is INTEGER
          The dimension of the work array WORK.  LWORK = 2*NW
          suffices, but greater efficiency may result from larger
          values of LWORK.

          If LWORK = -1, then a workspace query is assumed; ZLAQR3
          only estimates the optimal workspace size for the given
          values of N, NW, KTOP and KBOT.  The estimate is returned
          in WORK(1).  No error message related to LWORK is issued
          by XERBLA.  Neither H nor Z are 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

Definition at line 264 of file zlaqr3.f.

267*
268* -- LAPACK auxiliary routine --
269* -- LAPACK is a software package provided by Univ. of Tennessee, --
270* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
271*
272* .. Scalar Arguments ..
273 INTEGER IHIZ, ILOZ, KBOT, KTOP, LDH, LDT, LDV, LDWV,
274 $ LDZ, LWORK, N, ND, NH, NS, NV, NW
275 LOGICAL WANTT, WANTZ
276* ..
277* .. Array Arguments ..
278 COMPLEX*16 H( LDH, * ), SH( * ), T( LDT, * ), V( LDV, * ),
279 $ WORK( * ), WV( LDWV, * ), Z( LDZ, * )
280* ..
281*
282* ================================================================
283*
284* .. Parameters ..
285 COMPLEX*16 ZERO, ONE
286 parameter( zero = ( 0.0d0, 0.0d0 ),
287 $ one = ( 1.0d0, 0.0d0 ) )
288 DOUBLE PRECISION RZERO, RONE
289 parameter( rzero = 0.0d0, rone = 1.0d0 )
290* ..
291* .. Local Scalars ..
292 COMPLEX*16 BETA, CDUM, S, TAU
293 DOUBLE PRECISION FOO, SAFMAX, SAFMIN, SMLNUM, ULP
294 INTEGER I, IFST, ILST, INFO, INFQR, J, JW, KCOL, KLN,
295 $ KNT, KROW, KWTOP, LTOP, LWK1, LWK2, LWK3,
296 $ LWKOPT, NMIN
297* ..
298* .. External Functions ..
299 DOUBLE PRECISION DLAMCH
300 INTEGER ILAENV
301 EXTERNAL dlamch, ilaenv
302* ..
303* .. External Subroutines ..
304 EXTERNAL dlabad, zcopy, zgehrd, zgemm, zlacpy, zlahqr,
305 $ zlaqr4, zlarf, zlarfg, zlaset, ztrexc, zunmhr
306* ..
307* .. Intrinsic Functions ..
308 INTRINSIC abs, dble, dcmplx, dconjg, dimag, int, max, min
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*
318* ==== Estimate optimal workspace. ====
319*
320 jw = min( nw, kbot-ktop+1 )
321 IF( jw.LE.2 ) THEN
322 lwkopt = 1
323 ELSE
324*
325* ==== Workspace query call to ZGEHRD ====
326*
327 CALL zgehrd( jw, 1, jw-1, t, ldt, work, work, -1, info )
328 lwk1 = int( work( 1 ) )
329*
330* ==== Workspace query call to ZUNMHR ====
331*
332 CALL zunmhr( 'R', 'N', jw, jw, 1, jw-1, t, ldt, work, v, ldv,
333 $ work, -1, info )
334 lwk2 = int( work( 1 ) )
335*
336* ==== Workspace query call to ZLAQR4 ====
337*
338 CALL zlaqr4( .true., .true., jw, 1, jw, t, ldt, sh, 1, jw, v,
339 $ ldv, work, -1, infqr )
340 lwk3 = int( work( 1 ) )
341*
342* ==== Optimal workspace ====
343*
344 lwkopt = max( jw+max( lwk1, lwk2 ), lwk3 )
345 END IF
346*
347* ==== Quick return in case of workspace query. ====
348*
349 IF( lwork.EQ.-1 ) THEN
350 work( 1 ) = dcmplx( lwkopt, 0 )
351 RETURN
352 END IF
353*
354* ==== Nothing to do ...
355* ... for an empty active block ... ====
356 ns = 0
357 nd = 0
358 work( 1 ) = one
359 IF( ktop.GT.kbot )
360 $ RETURN
361* ... nor for an empty deflation window. ====
362 IF( nw.LT.1 )
363 $ RETURN
364*
365* ==== Machine constants ====
366*
367 safmin = dlamch( 'SAFE MINIMUM' )
368 safmax = rone / safmin
369 CALL dlabad( safmin, safmax )
370 ulp = dlamch( 'PRECISION' )
371 smlnum = safmin*( dble( n ) / ulp )
372*
373* ==== Setup deflation window ====
374*
375 jw = min( nw, kbot-ktop+1 )
376 kwtop = kbot - jw + 1
377 IF( kwtop.EQ.ktop ) THEN
378 s = zero
379 ELSE
380 s = h( kwtop, kwtop-1 )
381 END IF
382*
383 IF( kbot.EQ.kwtop ) THEN
384*
385* ==== 1-by-1 deflation window: not much to do ====
386*
387 sh( kwtop ) = h( kwtop, kwtop )
388 ns = 1
389 nd = 0
390 IF( cabs1( s ).LE.max( smlnum, ulp*cabs1( h( kwtop,
391 $ kwtop ) ) ) ) THEN
392 ns = 0
393 nd = 1
394 IF( kwtop.GT.ktop )
395 $ h( kwtop, kwtop-1 ) = zero
396 END IF
397 work( 1 ) = one
398 RETURN
399 END IF
400*
401* ==== Convert to spike-triangular form. (In case of a
402* . rare QR failure, this routine continues to do
403* . aggressive early deflation using that part of
404* . the deflation window that converged using INFQR
405* . here and there to keep track.) ====
406*
407 CALL zlacpy( 'U', jw, jw, h( kwtop, kwtop ), ldh, t, ldt )
408 CALL zcopy( jw-1, h( kwtop+1, kwtop ), ldh+1, t( 2, 1 ), ldt+1 )
409*
410 CALL zlaset( 'A', jw, jw, zero, one, v, ldv )
411 nmin = ilaenv( 12, 'ZLAQR3', 'SV', jw, 1, jw, lwork )
412 IF( jw.GT.nmin ) THEN
413 CALL zlaqr4( .true., .true., jw, 1, jw, t, ldt, sh( kwtop ), 1,
414 $ jw, v, ldv, work, lwork, infqr )
415 ELSE
416 CALL zlahqr( .true., .true., jw, 1, jw, t, ldt, sh( kwtop ), 1,
417 $ jw, v, ldv, infqr )
418 END IF
419*
420* ==== Deflation detection loop ====
421*
422 ns = jw
423 ilst = infqr + 1
424 DO 10 knt = infqr + 1, jw
425*
426* ==== Small spike tip deflation test ====
427*
428 foo = cabs1( t( ns, ns ) )
429 IF( foo.EQ.rzero )
430 $ foo = cabs1( s )
431 IF( cabs1( s )*cabs1( v( 1, ns ) ).LE.max( smlnum, ulp*foo ) )
432 $ THEN
433*
434* ==== One more converged eigenvalue ====
435*
436 ns = ns - 1
437 ELSE
438*
439* ==== One undeflatable eigenvalue. Move it up out of the
440* . way. (ZTREXC can not fail in this case.) ====
441*
442 ifst = ns
443 CALL ztrexc( 'V', jw, t, ldt, v, ldv, ifst, ilst, info )
444 ilst = ilst + 1
445 END IF
446 10 CONTINUE
447*
448* ==== Return to Hessenberg form ====
449*
450 IF( ns.EQ.0 )
451 $ s = zero
452*
453 IF( ns.LT.jw ) THEN
454*
455* ==== sorting the diagonal of T improves accuracy for
456* . graded matrices. ====
457*
458 DO 30 i = infqr + 1, ns
459 ifst = i
460 DO 20 j = i + 1, ns
461 IF( cabs1( t( j, j ) ).GT.cabs1( t( ifst, ifst ) ) )
462 $ ifst = j
463 20 CONTINUE
464 ilst = i
465 IF( ifst.NE.ilst )
466 $ CALL ztrexc( 'V', jw, t, ldt, v, ldv, ifst, ilst, info )
467 30 CONTINUE
468 END IF
469*
470* ==== Restore shift/eigenvalue array from T ====
471*
472 DO 40 i = infqr + 1, jw
473 sh( kwtop+i-1 ) = t( i, i )
474 40 CONTINUE
475*
476*
477 IF( ns.LT.jw .OR. s.EQ.zero ) THEN
478 IF( ns.GT.1 .AND. s.NE.zero ) THEN
479*
480* ==== Reflect spike back into lower triangle ====
481*
482 CALL zcopy( ns, v, ldv, work, 1 )
483 DO 50 i = 1, ns
484 work( i ) = dconjg( work( i ) )
485 50 CONTINUE
486 beta = work( 1 )
487 CALL zlarfg( ns, beta, work( 2 ), 1, tau )
488 work( 1 ) = one
489*
490 CALL zlaset( 'L', jw-2, jw-2, zero, zero, t( 3, 1 ), ldt )
491*
492 CALL zlarf( 'L', ns, jw, work, 1, dconjg( tau ), t, ldt,
493 $ work( jw+1 ) )
494 CALL zlarf( 'R', ns, ns, work, 1, tau, t, ldt,
495 $ work( jw+1 ) )
496 CALL zlarf( 'R', jw, ns, work, 1, tau, v, ldv,
497 $ work( jw+1 ) )
498*
499 CALL zgehrd( jw, 1, ns, t, ldt, work, work( jw+1 ),
500 $ lwork-jw, info )
501 END IF
502*
503* ==== Copy updated reduced window into place ====
504*
505 IF( kwtop.GT.1 )
506 $ h( kwtop, kwtop-1 ) = s*dconjg( v( 1, 1 ) )
507 CALL zlacpy( 'U', jw, jw, t, ldt, h( kwtop, kwtop ), ldh )
508 CALL zcopy( jw-1, t( 2, 1 ), ldt+1, h( kwtop+1, kwtop ),
509 $ ldh+1 )
510*
511* ==== Accumulate orthogonal matrix in order update
512* . H and Z, if requested. ====
513*
514 IF( ns.GT.1 .AND. s.NE.zero )
515 $ CALL zunmhr( 'R', 'N', jw, ns, 1, ns, t, ldt, work, v, ldv,
516 $ work( jw+1 ), lwork-jw, info )
517*
518* ==== Update vertical slab in H ====
519*
520 IF( wantt ) THEN
521 ltop = 1
522 ELSE
523 ltop = ktop
524 END IF
525 DO 60 krow = ltop, kwtop - 1, nv
526 kln = min( nv, kwtop-krow )
527 CALL zgemm( 'N', 'N', kln, jw, jw, one, h( krow, kwtop ),
528 $ ldh, v, ldv, zero, wv, ldwv )
529 CALL zlacpy( 'A', kln, jw, wv, ldwv, h( krow, kwtop ), ldh )
530 60 CONTINUE
531*
532* ==== Update horizontal slab in H ====
533*
534 IF( wantt ) THEN
535 DO 70 kcol = kbot + 1, n, nh
536 kln = min( nh, n-kcol+1 )
537 CALL zgemm( 'C', 'N', jw, kln, jw, one, v, ldv,
538 $ h( kwtop, kcol ), ldh, zero, t, ldt )
539 CALL zlacpy( 'A', jw, kln, t, ldt, h( kwtop, kcol ),
540 $ ldh )
541 70 CONTINUE
542 END IF
543*
544* ==== Update vertical slab in Z ====
545*
546 IF( wantz ) THEN
547 DO 80 krow = iloz, ihiz, nv
548 kln = min( nv, ihiz-krow+1 )
549 CALL zgemm( 'N', 'N', kln, jw, jw, one, z( krow, kwtop ),
550 $ ldz, v, ldv, zero, wv, ldwv )
551 CALL zlacpy( 'A', kln, jw, wv, ldwv, z( krow, kwtop ),
552 $ ldz )
553 80 CONTINUE
554 END IF
555 END IF
556*
557* ==== Return the number of deflations ... ====
558*
559 nd = jw - ns
560*
561* ==== ... and the number of shifts. (Subtracting
562* . INFQR from the spike length takes care
563* . of the case of a rare QR failure while
564* . calculating eigenvalues of the deflation
565* . window.) ====
566*
567 ns = ns - infqr
568*
569* ==== Return optimal workspace. ====
570*
571 work( 1 ) = dcmplx( lwkopt, 0 )
572*
573* ==== End of ZLAQR3 ====
574*
dlamch
double precision function dlamch(CMACH)
DLAMCH
Definition: dlamch.f:69
dlabad
subroutine dlabad(SMALL, LARGE)
DLABAD
Definition: dlabad.f:74
ilaenv
integer function ilaenv(ISPEC, NAME, OPTS, N1, N2, N3, N4)
ILAENV
Definition: ilaenv.f:162
zcopy
subroutine zcopy(N, ZX, INCX, ZY, INCY)
ZCOPY
Definition: zcopy.f:81
zgemm
subroutine zgemm(TRANSA, TRANSB, M, N, K, ALPHA, A, LDA, B, LDB, BETA, C, LDC)
ZGEMM
Definition: zgemm.f:187
zgehrd
subroutine zgehrd(N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO)
ZGEHRD
Definition: zgehrd.f:167
zlahqr
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
zlacpy
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
zlaset
subroutine zlaset(UPLO, M, N, ALPHA, BETA, A, LDA)
ZLASET initializes the off-diagonal elements and the diagonal elements of a matrix to given values.
Definition: zlaset.f:106
zlarf
subroutine zlarf(SIDE, M, N, V, INCV, TAU, C, LDC, WORK)
ZLARF applies an elementary reflector to a general rectangular matrix.
Definition: zlarf.f:128
zlarfg
subroutine zlarfg(N, ALPHA, X, INCX, TAU)
ZLARFG generates an elementary reflector (Householder matrix).
Definition: zlarfg.f:106
zlaqr4
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
ztrexc
subroutine ztrexc(COMPQ, N, T, LDT, Q, LDQ, IFST, ILST, INFO)
ZTREXC
Definition: ztrexc.f:126
zunmhr
subroutine zunmhr(SIDE, TRANS, M, N, ILO, IHI, A, LDA, TAU, C, LDC, WORK, LWORK, INFO)
ZUNMHR
Definition: zunmhr.f:178
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