Annotation of rpl/lapack/lapack/zlaqr2.f, revision 1.8

1.8     ! bertrand    1: *> \brief \b ZLAQR2
        !             2: *
        !             3: *  =========== DOCUMENTATION ===========
        !             4: *
        !             5: * Online html documentation available at 
        !             6: *            http://www.netlib.org/lapack/explore-html/ 
        !             7: *
        !             8: *> \htmlonly
        !             9: *> Download ZLAQR2 + dependencies 
        !            10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/zlaqr2.f"> 
        !            11: *> [TGZ]</a> 
        !            12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/zlaqr2.f"> 
        !            13: *> [ZIP]</a> 
        !            14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zlaqr2.f"> 
        !            15: *> [TXT]</a>
        !            16: *> \endhtmlonly 
        !            17: *
        !            18: *  Definition:
        !            19: *  ===========
        !            20: *
        !            21: *       SUBROUTINE ZLAQR2( WANTT, WANTZ, N, KTOP, KBOT, NW, H, LDH, ILOZ,
        !            22: *                          IHIZ, Z, LDZ, NS, ND, SH, V, LDV, NH, T, LDT,
        !            23: *                          NV, WV, LDWV, WORK, LWORK )
        !            24: * 
        !            25: *       .. Scalar Arguments ..
        !            26: *       INTEGER            IHIZ, ILOZ, KBOT, KTOP, LDH, LDT, LDV, LDWV,
        !            27: *      $                   LDZ, LWORK, N, ND, NH, NS, NV, NW
        !            28: *       LOGICAL            WANTT, WANTZ
        !            29: *       ..
        !            30: *       .. Array Arguments ..
        !            31: *       COMPLEX*16         H( LDH, * ), SH( * ), T( LDT, * ), V( LDV, * ),
        !            32: *      $                   WORK( * ), WV( LDWV, * ), Z( LDZ, * )
        !            33: *       ..
        !            34: *  
        !            35: *
        !            36: *> \par Purpose:
        !            37: *  =============
        !            38: *>
        !            39: *> \verbatim
        !            40: *>
        !            41: *>    ZLAQR2 is identical to ZLAQR3 except that it avoids
        !            42: *>    recursion by calling ZLAHQR instead of ZLAQR4.
        !            43: *>
        !            44: *>    Aggressive early deflation:
        !            45: *>
        !            46: *>    ZLAQR2 accepts as input an upper Hessenberg matrix
        !            47: *>    H and performs an unitary similarity transformation
        !            48: *>    designed to detect and deflate fully converged eigenvalues from
        !            49: *>    a trailing principal submatrix.  On output H has been over-
        !            50: *>    written by a new Hessenberg matrix that is a perturbation of
        !            51: *>    an unitary similarity transformation of H.  It is to be
        !            52: *>    hoped that the final version of H has many zero subdiagonal
        !            53: *>    entries.
        !            54: *>
        !            55: *> \endverbatim
        !            56: *
        !            57: *  Arguments:
        !            58: *  ==========
        !            59: *
        !            60: *> \param[in] WANTT
        !            61: *> \verbatim
        !            62: *>          WANTT is LOGICAL
        !            63: *>          If .TRUE., then the Hessenberg matrix H is fully updated
        !            64: *>          so that the triangular Schur factor may be
        !            65: *>          computed (in cooperation with the calling subroutine).
        !            66: *>          If .FALSE., then only enough of H is updated to preserve
        !            67: *>          the eigenvalues.
        !            68: *> \endverbatim
        !            69: *>
        !            70: *> \param[in] WANTZ
        !            71: *> \verbatim
        !            72: *>          WANTZ is LOGICAL
        !            73: *>          If .TRUE., then the unitary matrix Z is updated so
        !            74: *>          so that the unitary Schur factor may be computed
        !            75: *>          (in cooperation with the calling subroutine).
        !            76: *>          If .FALSE., then Z is not referenced.
        !            77: *> \endverbatim
        !            78: *>
        !            79: *> \param[in] N
        !            80: *> \verbatim
        !            81: *>          N is INTEGER
        !            82: *>          The order of the matrix H and (if WANTZ is .TRUE.) the
        !            83: *>          order of the unitary matrix Z.
        !            84: *> \endverbatim
        !            85: *>
        !            86: *> \param[in] KTOP
        !            87: *> \verbatim
        !            88: *>          KTOP is INTEGER
        !            89: *>          It is assumed that either KTOP = 1 or H(KTOP,KTOP-1)=0.
        !            90: *>          KBOT and KTOP together determine an isolated block
        !            91: *>          along the diagonal of the Hessenberg matrix.
        !            92: *> \endverbatim
        !            93: *>
        !            94: *> \param[in] KBOT
        !            95: *> \verbatim
        !            96: *>          KBOT is INTEGER
        !            97: *>          It is assumed without a check that either
        !            98: *>          KBOT = N or H(KBOT+1,KBOT)=0.  KBOT and KTOP together
        !            99: *>          determine an isolated block along the diagonal of the
        !           100: *>          Hessenberg matrix.
        !           101: *> \endverbatim
        !           102: *>
        !           103: *> \param[in] NW
        !           104: *> \verbatim
        !           105: *>          NW is INTEGER
        !           106: *>          Deflation window size.  1 .LE. NW .LE. (KBOT-KTOP+1).
        !           107: *> \endverbatim
        !           108: *>
        !           109: *> \param[in,out] H
        !           110: *> \verbatim
        !           111: *>          H is COMPLEX*16 array, dimension (LDH,N)
        !           112: *>          On input the initial N-by-N section of H stores the
        !           113: *>          Hessenberg matrix undergoing aggressive early deflation.
        !           114: *>          On output H has been transformed by a unitary
        !           115: *>          similarity transformation, perturbed, and the returned
        !           116: *>          to Hessenberg form that (it is to be hoped) has some
        !           117: *>          zero subdiagonal entries.
        !           118: *> \endverbatim
        !           119: *>
        !           120: *> \param[in] LDH
        !           121: *> \verbatim
        !           122: *>          LDH is integer
        !           123: *>          Leading dimension of H just as declared in the calling
        !           124: *>          subroutine.  N .LE. LDH
        !           125: *> \endverbatim
        !           126: *>
        !           127: *> \param[in] ILOZ
        !           128: *> \verbatim
        !           129: *>          ILOZ is INTEGER
        !           130: *> \endverbatim
        !           131: *>
        !           132: *> \param[in] IHIZ
        !           133: *> \verbatim
        !           134: *>          IHIZ is INTEGER
        !           135: *>          Specify the rows of Z to which transformations must be
        !           136: *>          applied if WANTZ is .TRUE.. 1 .LE. ILOZ .LE. IHIZ .LE. N.
        !           137: *> \endverbatim
        !           138: *>
        !           139: *> \param[in,out] Z
        !           140: *> \verbatim
        !           141: *>          Z is COMPLEX*16 array, dimension (LDZ,N)
        !           142: *>          IF WANTZ is .TRUE., then on output, the unitary
        !           143: *>          similarity transformation mentioned above has been
        !           144: *>          accumulated into Z(ILOZ:IHIZ,ILO:IHI) from the right.
        !           145: *>          If WANTZ is .FALSE., then Z is unreferenced.
        !           146: *> \endverbatim
        !           147: *>
        !           148: *> \param[in] LDZ
        !           149: *> \verbatim
        !           150: *>          LDZ is integer
        !           151: *>          The leading dimension of Z just as declared in the
        !           152: *>          calling subroutine.  1 .LE. LDZ.
        !           153: *> \endverbatim
        !           154: *>
        !           155: *> \param[out] NS
        !           156: *> \verbatim
        !           157: *>          NS is integer
        !           158: *>          The number of unconverged (ie approximate) eigenvalues
        !           159: *>          returned in SR and SI that may be used as shifts by the
        !           160: *>          calling subroutine.
        !           161: *> \endverbatim
        !           162: *>
        !           163: *> \param[out] ND
        !           164: *> \verbatim
        !           165: *>          ND is integer
        !           166: *>          The number of converged eigenvalues uncovered by this
        !           167: *>          subroutine.
        !           168: *> \endverbatim
        !           169: *>
        !           170: *> \param[out] SH
        !           171: *> \verbatim
        !           172: *>          SH is COMPLEX*16 array, dimension KBOT
        !           173: *>          On output, approximate eigenvalues that may
        !           174: *>          be used for shifts are stored in SH(KBOT-ND-NS+1)
        !           175: *>          through SR(KBOT-ND).  Converged eigenvalues are
        !           176: *>          stored in SH(KBOT-ND+1) through SH(KBOT).
        !           177: *> \endverbatim
        !           178: *>
        !           179: *> \param[out] V
        !           180: *> \verbatim
        !           181: *>          V is COMPLEX*16 array, dimension (LDV,NW)
        !           182: *>          An NW-by-NW work array.
        !           183: *> \endverbatim
        !           184: *>
        !           185: *> \param[in] LDV
        !           186: *> \verbatim
        !           187: *>          LDV is integer scalar
        !           188: *>          The leading dimension of V just as declared in the
        !           189: *>          calling subroutine.  NW .LE. LDV
        !           190: *> \endverbatim
        !           191: *>
        !           192: *> \param[in] NH
        !           193: *> \verbatim
        !           194: *>          NH is integer scalar
        !           195: *>          The number of columns of T.  NH.GE.NW.
        !           196: *> \endverbatim
        !           197: *>
        !           198: *> \param[out] T
        !           199: *> \verbatim
        !           200: *>          T is COMPLEX*16 array, dimension (LDT,NW)
        !           201: *> \endverbatim
        !           202: *>
        !           203: *> \param[in] LDT
        !           204: *> \verbatim
        !           205: *>          LDT is integer
        !           206: *>          The leading dimension of T just as declared in the
        !           207: *>          calling subroutine.  NW .LE. LDT
        !           208: *> \endverbatim
        !           209: *>
        !           210: *> \param[in] NV
        !           211: *> \verbatim
        !           212: *>          NV is integer
        !           213: *>          The number of rows of work array WV available for
        !           214: *>          workspace.  NV.GE.NW.
        !           215: *> \endverbatim
        !           216: *>
        !           217: *> \param[out] WV
        !           218: *> \verbatim
        !           219: *>          WV is COMPLEX*16 array, dimension (LDWV,NW)
        !           220: *> \endverbatim
        !           221: *>
        !           222: *> \param[in] LDWV
        !           223: *> \verbatim
        !           224: *>          LDWV is integer
        !           225: *>          The leading dimension of W just as declared in the
        !           226: *>          calling subroutine.  NW .LE. LDV
        !           227: *> \endverbatim
        !           228: *>
        !           229: *> \param[out] WORK
        !           230: *> \verbatim
        !           231: *>          WORK is COMPLEX*16 array, dimension LWORK.
        !           232: *>          On exit, WORK(1) is set to an estimate of the optimal value
        !           233: *>          of LWORK for the given values of N, NW, KTOP and KBOT.
        !           234: *> \endverbatim
        !           235: *>
        !           236: *> \param[in] LWORK
        !           237: *> \verbatim
        !           238: *>          LWORK is integer
        !           239: *>          The dimension of the work array WORK.  LWORK = 2*NW
        !           240: *>          suffices, but greater efficiency may result from larger
        !           241: *>          values of LWORK.
        !           242: *>
        !           243: *>          If LWORK = -1, then a workspace query is assumed; ZLAQR2
        !           244: *>          only estimates the optimal workspace size for the given
        !           245: *>          values of N, NW, KTOP and KBOT.  The estimate is returned
        !           246: *>          in WORK(1).  No error message related to LWORK is issued
        !           247: *>          by XERBLA.  Neither H nor Z are accessed.
        !           248: *> \endverbatim
        !           249: *
        !           250: *  Authors:
        !           251: *  ========
        !           252: *
        !           253: *> \author Univ. of Tennessee 
        !           254: *> \author Univ. of California Berkeley 
        !           255: *> \author Univ. of Colorado Denver 
        !           256: *> \author NAG Ltd. 
        !           257: *
        !           258: *> \date November 2011
        !           259: *
        !           260: *> \ingroup complex16OTHERauxiliary
        !           261: *
        !           262: *> \par Contributors:
        !           263: *  ==================
        !           264: *>
        !           265: *>       Karen Braman and Ralph Byers, Department of Mathematics,
        !           266: *>       University of Kansas, USA
        !           267: *>
        !           268: *  =====================================================================
1.1       bertrand  269:       SUBROUTINE ZLAQR2( WANTT, WANTZ, N, KTOP, KBOT, NW, H, LDH, ILOZ,
                    270:      $                   IHIZ, Z, LDZ, NS, ND, SH, V, LDV, NH, T, LDT,
                    271:      $                   NV, WV, LDWV, WORK, LWORK )
                    272: *
1.8     ! bertrand  273: *  -- LAPACK auxiliary routine (version 3.4.0) --
        !           274: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
        !           275: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
        !           276: *     November 2011
1.1       bertrand  277: *
                    278: *     .. Scalar Arguments ..
                    279:       INTEGER            IHIZ, ILOZ, KBOT, KTOP, LDH, LDT, LDV, LDWV,
                    280:      $                   LDZ, LWORK, N, ND, NH, NS, NV, NW
                    281:       LOGICAL            WANTT, WANTZ
                    282: *     ..
                    283: *     .. Array Arguments ..
                    284:       COMPLEX*16         H( LDH, * ), SH( * ), T( LDT, * ), V( LDV, * ),
                    285:      $                   WORK( * ), WV( LDWV, * ), Z( LDZ, * )
                    286: *     ..
                    287: *
1.8     ! bertrand  288: *  ================================================================
1.1       bertrand  289: *
                    290: *     .. Parameters ..
                    291:       COMPLEX*16         ZERO, ONE
                    292:       PARAMETER          ( ZERO = ( 0.0d0, 0.0d0 ),
                    293:      $                   ONE = ( 1.0d0, 0.0d0 ) )
                    294:       DOUBLE PRECISION   RZERO, RONE
                    295:       PARAMETER          ( RZERO = 0.0d0, RONE = 1.0d0 )
                    296: *     ..
                    297: *     .. Local Scalars ..
                    298:       COMPLEX*16         BETA, CDUM, S, TAU
                    299:       DOUBLE PRECISION   FOO, SAFMAX, SAFMIN, SMLNUM, ULP
                    300:       INTEGER            I, IFST, ILST, INFO, INFQR, J, JW, KCOL, KLN,
                    301:      $                   KNT, KROW, KWTOP, LTOP, LWK1, LWK2, LWKOPT
                    302: *     ..
                    303: *     .. External Functions ..
                    304:       DOUBLE PRECISION   DLAMCH
                    305:       EXTERNAL           DLAMCH
                    306: *     ..
                    307: *     .. External Subroutines ..
                    308:       EXTERNAL           DLABAD, ZCOPY, ZGEHRD, ZGEMM, ZLACPY, ZLAHQR,
                    309:      $                   ZLARF, ZLARFG, ZLASET, ZTREXC, ZUNMHR
                    310: *     ..
                    311: *     .. Intrinsic Functions ..
                    312:       INTRINSIC          ABS, DBLE, DCMPLX, DCONJG, DIMAG, INT, MAX, MIN
                    313: *     ..
                    314: *     .. Statement Functions ..
                    315:       DOUBLE PRECISION   CABS1
                    316: *     ..
                    317: *     .. Statement Function definitions ..
                    318:       CABS1( CDUM ) = ABS( DBLE( CDUM ) ) + ABS( DIMAG( CDUM ) )
                    319: *     ..
                    320: *     .. Executable Statements ..
                    321: *
                    322: *     ==== Estimate optimal workspace. ====
                    323: *
                    324:       JW = MIN( NW, KBOT-KTOP+1 )
                    325:       IF( JW.LE.2 ) THEN
                    326:          LWKOPT = 1
                    327:       ELSE
                    328: *
                    329: *        ==== Workspace query call to ZGEHRD ====
                    330: *
                    331:          CALL ZGEHRD( JW, 1, JW-1, T, LDT, WORK, WORK, -1, INFO )
                    332:          LWK1 = INT( WORK( 1 ) )
                    333: *
                    334: *        ==== Workspace query call to ZUNMHR ====
                    335: *
                    336:          CALL ZUNMHR( 'R', 'N', JW, JW, 1, JW-1, T, LDT, WORK, V, LDV,
                    337:      $                WORK, -1, INFO )
                    338:          LWK2 = INT( WORK( 1 ) )
                    339: *
                    340: *        ==== Optimal workspace ====
                    341: *
                    342:          LWKOPT = JW + MAX( LWK1, LWK2 )
                    343:       END IF
                    344: *
                    345: *     ==== Quick return in case of workspace query. ====
                    346: *
                    347:       IF( LWORK.EQ.-1 ) THEN
                    348:          WORK( 1 ) = DCMPLX( LWKOPT, 0 )
                    349:          RETURN
                    350:       END IF
                    351: *
                    352: *     ==== Nothing to do ...
                    353: *     ... for an empty active block ... ====
                    354:       NS = 0
                    355:       ND = 0
                    356:       WORK( 1 ) = ONE
                    357:       IF( KTOP.GT.KBOT )
                    358:      $   RETURN
                    359: *     ... nor for an empty deflation window. ====
                    360:       IF( NW.LT.1 )
                    361:      $   RETURN
                    362: *
                    363: *     ==== Machine constants ====
                    364: *
                    365:       SAFMIN = DLAMCH( 'SAFE MINIMUM' )
                    366:       SAFMAX = RONE / SAFMIN
                    367:       CALL DLABAD( SAFMIN, SAFMAX )
                    368:       ULP = DLAMCH( 'PRECISION' )
                    369:       SMLNUM = SAFMIN*( DBLE( N ) / ULP )
                    370: *
                    371: *     ==== Setup deflation window ====
                    372: *
                    373:       JW = MIN( NW, KBOT-KTOP+1 )
                    374:       KWTOP = KBOT - JW + 1
                    375:       IF( KWTOP.EQ.KTOP ) THEN
                    376:          S = ZERO
                    377:       ELSE
                    378:          S = H( KWTOP, KWTOP-1 )
                    379:       END IF
                    380: *
                    381:       IF( KBOT.EQ.KWTOP ) THEN
                    382: *
                    383: *        ==== 1-by-1 deflation window: not much to do ====
                    384: *
                    385:          SH( KWTOP ) = H( KWTOP, KWTOP )
                    386:          NS = 1
                    387:          ND = 0
                    388:          IF( CABS1( S ).LE.MAX( SMLNUM, ULP*CABS1( H( KWTOP,
                    389:      $       KWTOP ) ) ) ) THEN
                    390:             NS = 0
                    391:             ND = 1
                    392:             IF( KWTOP.GT.KTOP )
                    393:      $         H( KWTOP, KWTOP-1 ) = ZERO
                    394:          END IF
                    395:          WORK( 1 ) = ONE
                    396:          RETURN
                    397:       END IF
                    398: *
                    399: *     ==== Convert to spike-triangular form.  (In case of a
                    400: *     .    rare QR failure, this routine continues to do
                    401: *     .    aggressive early deflation using that part of
                    402: *     .    the deflation window that converged using INFQR
                    403: *     .    here and there to keep track.) ====
                    404: *
                    405:       CALL ZLACPY( 'U', JW, JW, H( KWTOP, KWTOP ), LDH, T, LDT )
                    406:       CALL ZCOPY( JW-1, H( KWTOP+1, KWTOP ), LDH+1, T( 2, 1 ), LDT+1 )
                    407: *
                    408:       CALL ZLASET( 'A', JW, JW, ZERO, ONE, V, LDV )
                    409:       CALL ZLAHQR( .true., .true., JW, 1, JW, T, LDT, SH( KWTOP ), 1,
                    410:      $             JW, V, LDV, INFQR )
                    411: *
                    412: *     ==== Deflation detection loop ====
                    413: *
                    414:       NS = JW
                    415:       ILST = INFQR + 1
                    416:       DO 10 KNT = INFQR + 1, JW
                    417: *
                    418: *        ==== Small spike tip deflation test ====
                    419: *
                    420:          FOO = CABS1( T( NS, NS ) )
                    421:          IF( FOO.EQ.RZERO )
                    422:      $      FOO = CABS1( S )
                    423:          IF( CABS1( S )*CABS1( V( 1, NS ) ).LE.MAX( SMLNUM, ULP*FOO ) )
                    424:      $        THEN
                    425: *
                    426: *           ==== One more converged eigenvalue ====
                    427: *
                    428:             NS = NS - 1
                    429:          ELSE
                    430: *
                    431: *           ==== One undeflatable eigenvalue.  Move it up out of the
                    432: *           .    way.   (ZTREXC can not fail in this case.) ====
                    433: *
                    434:             IFST = NS
                    435:             CALL ZTREXC( 'V', JW, T, LDT, V, LDV, IFST, ILST, INFO )
                    436:             ILST = ILST + 1
                    437:          END IF
                    438:    10 CONTINUE
                    439: *
                    440: *        ==== Return to Hessenberg form ====
                    441: *
                    442:       IF( NS.EQ.0 )
                    443:      $   S = ZERO
                    444: *
                    445:       IF( NS.LT.JW ) THEN
                    446: *
                    447: *        ==== sorting the diagonal of T improves accuracy for
                    448: *        .    graded matrices.  ====
                    449: *
                    450:          DO 30 I = INFQR + 1, NS
                    451:             IFST = I
                    452:             DO 20 J = I + 1, NS
                    453:                IF( CABS1( T( J, J ) ).GT.CABS1( T( IFST, IFST ) ) )
                    454:      $            IFST = J
                    455:    20       CONTINUE
                    456:             ILST = I
                    457:             IF( IFST.NE.ILST )
                    458:      $         CALL ZTREXC( 'V', JW, T, LDT, V, LDV, IFST, ILST, INFO )
                    459:    30    CONTINUE
                    460:       END IF
                    461: *
                    462: *     ==== Restore shift/eigenvalue array from T ====
                    463: *
                    464:       DO 40 I = INFQR + 1, JW
                    465:          SH( KWTOP+I-1 ) = T( I, I )
                    466:    40 CONTINUE
                    467: *
                    468: *
                    469:       IF( NS.LT.JW .OR. S.EQ.ZERO ) THEN
                    470:          IF( NS.GT.1 .AND. S.NE.ZERO ) THEN
                    471: *
                    472: *           ==== Reflect spike back into lower triangle ====
                    473: *
                    474:             CALL ZCOPY( NS, V, LDV, WORK, 1 )
                    475:             DO 50 I = 1, NS
                    476:                WORK( I ) = DCONJG( WORK( I ) )
                    477:    50       CONTINUE
                    478:             BETA = WORK( 1 )
                    479:             CALL ZLARFG( NS, BETA, WORK( 2 ), 1, TAU )
                    480:             WORK( 1 ) = ONE
                    481: *
                    482:             CALL ZLASET( 'L', JW-2, JW-2, ZERO, ZERO, T( 3, 1 ), LDT )
                    483: *
                    484:             CALL ZLARF( 'L', NS, JW, WORK, 1, DCONJG( TAU ), T, LDT,
                    485:      $                  WORK( JW+1 ) )
                    486:             CALL ZLARF( 'R', NS, NS, WORK, 1, TAU, T, LDT,
                    487:      $                  WORK( JW+1 ) )
                    488:             CALL ZLARF( 'R', JW, NS, WORK, 1, TAU, V, LDV,
                    489:      $                  WORK( JW+1 ) )
                    490: *
                    491:             CALL ZGEHRD( JW, 1, NS, T, LDT, WORK, WORK( JW+1 ),
                    492:      $                   LWORK-JW, INFO )
                    493:          END IF
                    494: *
                    495: *        ==== Copy updated reduced window into place ====
                    496: *
                    497:          IF( KWTOP.GT.1 )
                    498:      $      H( KWTOP, KWTOP-1 ) = S*DCONJG( V( 1, 1 ) )
                    499:          CALL ZLACPY( 'U', JW, JW, T, LDT, H( KWTOP, KWTOP ), LDH )
                    500:          CALL ZCOPY( JW-1, T( 2, 1 ), LDT+1, H( KWTOP+1, KWTOP ),
                    501:      $               LDH+1 )
                    502: *
                    503: *        ==== Accumulate orthogonal matrix in order update
                    504: *        .    H and Z, if requested.  ====
                    505: *
                    506:          IF( NS.GT.1 .AND. S.NE.ZERO )
                    507:      $      CALL ZUNMHR( 'R', 'N', JW, NS, 1, NS, T, LDT, WORK, V, LDV,
                    508:      $                   WORK( JW+1 ), LWORK-JW, INFO )
                    509: *
                    510: *        ==== Update vertical slab in H ====
                    511: *
                    512:          IF( WANTT ) THEN
                    513:             LTOP = 1
                    514:          ELSE
                    515:             LTOP = KTOP
                    516:          END IF
                    517:          DO 60 KROW = LTOP, KWTOP - 1, NV
                    518:             KLN = MIN( NV, KWTOP-KROW )
                    519:             CALL ZGEMM( 'N', 'N', KLN, JW, JW, ONE, H( KROW, KWTOP ),
                    520:      $                  LDH, V, LDV, ZERO, WV, LDWV )
                    521:             CALL ZLACPY( 'A', KLN, JW, WV, LDWV, H( KROW, KWTOP ), LDH )
                    522:    60    CONTINUE
                    523: *
                    524: *        ==== Update horizontal slab in H ====
                    525: *
                    526:          IF( WANTT ) THEN
                    527:             DO 70 KCOL = KBOT + 1, N, NH
                    528:                KLN = MIN( NH, N-KCOL+1 )
                    529:                CALL ZGEMM( 'C', 'N', JW, KLN, JW, ONE, V, LDV,
                    530:      $                     H( KWTOP, KCOL ), LDH, ZERO, T, LDT )
                    531:                CALL ZLACPY( 'A', JW, KLN, T, LDT, H( KWTOP, KCOL ),
                    532:      $                      LDH )
                    533:    70       CONTINUE
                    534:          END IF
                    535: *
                    536: *        ==== Update vertical slab in Z ====
                    537: *
                    538:          IF( WANTZ ) THEN
                    539:             DO 80 KROW = ILOZ, IHIZ, NV
                    540:                KLN = MIN( NV, IHIZ-KROW+1 )
                    541:                CALL ZGEMM( 'N', 'N', KLN, JW, JW, ONE, Z( KROW, KWTOP ),
                    542:      $                     LDZ, V, LDV, ZERO, WV, LDWV )
                    543:                CALL ZLACPY( 'A', KLN, JW, WV, LDWV, Z( KROW, KWTOP ),
                    544:      $                      LDZ )
                    545:    80       CONTINUE
                    546:          END IF
                    547:       END IF
                    548: *
                    549: *     ==== Return the number of deflations ... ====
                    550: *
                    551:       ND = JW - NS
                    552: *
                    553: *     ==== ... and the number of shifts. (Subtracting
                    554: *     .    INFQR from the spike length takes care
                    555: *     .    of the case of a rare QR failure while
                    556: *     .    calculating eigenvalues of the deflation
                    557: *     .    window.)  ====
                    558: *
                    559:       NS = NS - INFQR
                    560: *
                    561: *      ==== Return optimal workspace. ====
                    562: *
                    563:       WORK( 1 ) = DCMPLX( LWKOPT, 0 )
                    564: *
                    565: *     ==== End of ZLAQR2 ====
                    566: *
                    567:       END

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