LAPACK: SRC/dlaqr3.f Source File

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00001       SUBROUTINE DLAQR3( WANTT, WANTZ, N, KTOP, KBOT, NW, H, LDH, ILOZ,
00002      $                   IHIZ, Z, LDZ, NS, ND, SR, SI, V, LDV, NH, T,
00003      $                   LDT, NV, WV, LDWV, WORK, LWORK )
00004 *
00005 *  -- LAPACK auxiliary routine (version 3.2.2)                        --
00006 *     Univ. of Tennessee, Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..
00007 *  -- June 2010                                                       --
00008 *
00009 *     .. Scalar Arguments ..
00010       INTEGER            IHIZ, ILOZ, KBOT, KTOP, LDH, LDT, LDV, LDWV,
00011      $                   LDZ, LWORK, N, ND, NH, NS, NV, NW
00012       LOGICAL            WANTT, WANTZ
00013 *     ..
00014 *     .. Array Arguments ..
00015       DOUBLE PRECISION   H( LDH, * ), SI( * ), SR( * ), T( LDT, * ),
00016      $                   V( LDV, * ), WORK( * ), WV( LDWV, * ),
00017      $                   Z( LDZ, * )
00018 *     ..
00019 *
00020 *     ******************************************************************
00021 *     Aggressive early deflation:
00022 *
00023 *     This subroutine accepts as input an upper Hessenberg matrix
00024 *     H and performs an orthogonal similarity transformation
00025 *     designed to detect and deflate fully converged eigenvalues from
00026 *     a trailing principal submatrix.  On output H has been over-
00027 *     written by a new Hessenberg matrix that is a perturbation of
00028 *     an orthogonal similarity transformation of H.  It is to be
00029 *     hoped that the final version of H has many zero subdiagonal
00030 *     entries.
00031 *
00032 *     ******************************************************************
00033 *     WANTT   (input) LOGICAL
00034 *          If .TRUE., then the Hessenberg matrix H is fully updated
00035 *          so that the quasi-triangular Schur factor may be
00036 *          computed (in cooperation with the calling subroutine).
00037 *          If .FALSE., then only enough of H is updated to preserve
00038 *          the eigenvalues.
00039 *
00040 *     WANTZ   (input) LOGICAL
00041 *          If .TRUE., then the orthogonal matrix Z is updated so
00042 *          so that the orthogonal Schur factor may be computed
00043 *          (in cooperation with the calling subroutine).
00044 *          If .FALSE., then Z is not referenced.
00045 *
00046 *     N       (input) INTEGER
00047 *          The order of the matrix H and (if WANTZ is .TRUE.) the
00048 *          order of the orthogonal matrix Z.
00049 *
00050 *     KTOP    (input) INTEGER
00051 *          It is assumed that either KTOP = 1 or H(KTOP,KTOP-1)=0.
00052 *          KBOT and KTOP together determine an isolated block
00053 *          along the diagonal of the Hessenberg matrix.
00054 *
00055 *     KBOT    (input) INTEGER
00056 *          It is assumed without a check that either
00057 *          KBOT = N or H(KBOT+1,KBOT)=0.  KBOT and KTOP together
00058 *          determine an isolated block along the diagonal of the
00059 *          Hessenberg matrix.
00060 *
00061 *     NW      (input) INTEGER
00062 *          Deflation window size.  1 .LE. NW .LE. (KBOT-KTOP+1).
00063 *
00064 *     H       (input/output) DOUBLE PRECISION array, dimension (LDH,N)
00065 *          On input the initial N-by-N section of H stores the
00066 *          Hessenberg matrix undergoing aggressive early deflation.
00067 *          On output H has been transformed by an orthogonal
00068 *          similarity transformation, perturbed, and the returned
00069 *          to Hessenberg form that (it is to be hoped) has some
00070 *          zero subdiagonal entries.
00071 *
00072 *     LDH     (input) integer
00073 *          Leading dimension of H just as declared in the calling
00074 *          subroutine.  N .LE. LDH
00075 *
00076 *     ILOZ    (input) INTEGER
00077 *     IHIZ    (input) INTEGER
00078 *          Specify the rows of Z to which transformations must be
00079 *          applied if WANTZ is .TRUE.. 1 .LE. ILOZ .LE. IHIZ .LE. N.
00080 *
00081 *     Z       (input/output) DOUBLE PRECISION array, dimension (LDZ,N)
00082 *          IF WANTZ is .TRUE., then on output, the orthogonal
00083 *          similarity transformation mentioned above has been
00084 *          accumulated into Z(ILOZ:IHIZ,ILO:IHI) from the right.
00085 *          If WANTZ is .FALSE., then Z is unreferenced.
00086 *
00087 *     LDZ     (input) integer
00088 *          The leading dimension of Z just as declared in the
00089 *          calling subroutine.  1 .LE. LDZ.
00090 *
00091 *     NS      (output) integer
00092 *          The number of unconverged (ie approximate) eigenvalues
00093 *          returned in SR and SI that may be used as shifts by the
00094 *          calling subroutine.
00095 *
00096 *     ND      (output) integer
00097 *          The number of converged eigenvalues uncovered by this
00098 *          subroutine.
00099 *
00100 *     SR      (output) DOUBLE PRECISION array, dimension (KBOT)
00101 *     SI      (output) DOUBLE PRECISION array, dimension (KBOT)
00102 *          On output, the real and imaginary parts of approximate
00103 *          eigenvalues that may be used for shifts are stored in
00104 *          SR(KBOT-ND-NS+1) through SR(KBOT-ND) and
00105 *          SI(KBOT-ND-NS+1) through SI(KBOT-ND), respectively.
00106 *          The real and imaginary parts of converged eigenvalues
00107 *          are stored in SR(KBOT-ND+1) through SR(KBOT) and
00108 *          SI(KBOT-ND+1) through SI(KBOT), respectively.
00109 *
00110 *     V       (workspace) DOUBLE PRECISION array, dimension (LDV,NW)
00111 *          An NW-by-NW work array.
00112 *
00113 *     LDV     (input) integer scalar
00114 *          The leading dimension of V just as declared in the
00115 *          calling subroutine.  NW .LE. LDV
00116 *
00117 *     NH      (input) integer scalar
00118 *          The number of columns of T.  NH.GE.NW.
00119 *
00120 *     T       (workspace) DOUBLE PRECISION array, dimension (LDT,NW)
00121 *
00122 *     LDT     (input) integer
00123 *          The leading dimension of T just as declared in the
00124 *          calling subroutine.  NW .LE. LDT
00125 *
00126 *     NV      (input) integer
00127 *          The number of rows of work array WV available for
00128 *          workspace.  NV.GE.NW.
00129 *
00130 *     WV      (workspace) DOUBLE PRECISION array, dimension (LDWV,NW)
00131 *
00132 *     LDWV    (input) integer
00133 *          The leading dimension of W just as declared in the
00134 *          calling subroutine.  NW .LE. LDV
00135 *
00136 *     WORK    (workspace) DOUBLE PRECISION array, dimension (LWORK)
00137 *          On exit, WORK(1) is set to an estimate of the optimal value
00138 *          of LWORK for the given values of N, NW, KTOP and KBOT.
00139 *
00140 *     LWORK   (input) integer
00141 *          The dimension of the work array WORK.  LWORK = 2*NW
00142 *          suffices, but greater efficiency may result from larger
00143 *          values of LWORK.
00144 *
00145 *          If LWORK = -1, then a workspace query is assumed; DLAQR3
00146 *          only estimates the optimal workspace size for the given
00147 *          values of N, NW, KTOP and KBOT.  The estimate is returned
00148 *          in WORK(1).  No error message related to LWORK is issued
00149 *          by XERBLA.  Neither H nor Z are accessed.
00150 *
00151 *     ================================================================
00152 *     Based on contributions by
00153 *        Karen Braman and Ralph Byers, Department of Mathematics,
00154 *        University of Kansas, USA
00155 *
00156 *     ================================================================
00157 *     .. Parameters ..
00158       DOUBLE PRECISION   ZERO, ONE
00159       PARAMETER          ( ZERO = 0.0d0, ONE = 1.0d0 )
00160 *     ..
00161 *     .. Local Scalars ..
00162       DOUBLE PRECISION   AA, BB, BETA, CC, CS, DD, EVI, EVK, FOO, S,
00163      $                   SAFMAX, SAFMIN, SMLNUM, SN, TAU, ULP
00164       INTEGER            I, IFST, ILST, INFO, INFQR, J, JW, K, KCOL,
00165      $                   KEND, KLN, KROW, KWTOP, LTOP, LWK1, LWK2, LWK3,
00166      $                   LWKOPT, NMIN
00167       LOGICAL            BULGE, SORTED
00168 *     ..
00169 *     .. External Functions ..
00170       DOUBLE PRECISION   DLAMCH
00171       INTEGER            ILAENV
00172       EXTERNAL           DLAMCH, ILAENV
00173 *     ..
00174 *     .. External Subroutines ..
00175       EXTERNAL           DCOPY, DGEHRD, DGEMM, DLABAD, DLACPY, DLAHQR,
00176      $                   DLANV2, DLAQR4, DLARF, DLARFG, DLASET, DORMHR,
00177      $                   DTREXC
00178 *     ..
00179 *     .. Intrinsic Functions ..
00180       INTRINSIC          ABS, DBLE, INT, MAX, MIN, SQRT
00181 *     ..
00182 *     .. Executable Statements ..
00183 *
00184 *     ==== Estimate optimal workspace. ====
00185 *
00186       JW = MIN( NW, KBOT-KTOP+1 )
00187       IF( JW.LE.2 ) THEN
00188          LWKOPT = 1
00189       ELSE
00190 *
00191 *        ==== Workspace query call to DGEHRD ====
00192 *
00193          CALL DGEHRD( JW, 1, JW-1, T, LDT, WORK, WORK, -1, INFO )
00194          LWK1 = INT( WORK( 1 ) )
00195 *
00196 *        ==== Workspace query call to DORMHR ====
00197 *
00198          CALL DORMHR( 'R', 'N', JW, JW, 1, JW-1, T, LDT, WORK, V, LDV,
00199      $                WORK, -1, INFO )
00200          LWK2 = INT( WORK( 1 ) )
00201 *
00202 *        ==== Workspace query call to DLAQR4 ====
00203 *
00204          CALL DLAQR4( .true., .true., JW, 1, JW, T, LDT, SR, SI, 1, JW,
00205      $                V, LDV, WORK, -1, INFQR )
00206          LWK3 = INT( WORK( 1 ) )
00207 *
00208 *        ==== Optimal workspace ====
00209 *
00210          LWKOPT = MAX( JW+MAX( LWK1, LWK2 ), LWK3 )
00211       END IF
00212 *
00213 *     ==== Quick return in case of workspace query. ====
00214 *
00215       IF( LWORK.EQ.-1 ) THEN
00216          WORK( 1 ) = DBLE( LWKOPT )
00217          RETURN
00218       END IF
00219 *
00220 *     ==== Nothing to do ...
00221 *     ... for an empty active block ... ====
00222       NS = 0
00223       ND = 0
00224       WORK( 1 ) = ONE
00225       IF( KTOP.GT.KBOT )
00226      $   RETURN
00227 *     ... nor for an empty deflation window. ====
00228       IF( NW.LT.1 )
00229      $   RETURN
00230 *
00231 *     ==== Machine constants ====
00232 *
00233       SAFMIN = DLAMCH( 'SAFE MINIMUM' )
00234       SAFMAX = ONE / SAFMIN
00235       CALL DLABAD( SAFMIN, SAFMAX )
00236       ULP = DLAMCH( 'PRECISION' )
00237       SMLNUM = SAFMIN*( DBLE( N ) / ULP )
00238 *
00239 *     ==== Setup deflation window ====
00240 *
00241       JW = MIN( NW, KBOT-KTOP+1 )
00242       KWTOP = KBOT - JW + 1
00243       IF( KWTOP.EQ.KTOP ) THEN
00244          S = ZERO
00245       ELSE
00246          S = H( KWTOP, KWTOP-1 )
00247       END IF
00248 *
00249       IF( KBOT.EQ.KWTOP ) THEN
00250 *
00251 *        ==== 1-by-1 deflation window: not much to do ====
00252 *
00253          SR( KWTOP ) = H( KWTOP, KWTOP )
00254          SI( KWTOP ) = ZERO
00255          NS = 1
00256          ND = 0
00257          IF( ABS( S ).LE.MAX( SMLNUM, ULP*ABS( H( KWTOP, KWTOP ) ) ) )
00258      $        THEN
00259             NS = 0
00260             ND = 1
00261             IF( KWTOP.GT.KTOP )
00262      $         H( KWTOP, KWTOP-1 ) = ZERO
00263          END IF
00264          WORK( 1 ) = ONE
00265          RETURN
00266       END IF
00267 *
00268 *     ==== Convert to spike-triangular form.  (In case of a
00269 *     .    rare QR failure, this routine continues to do
00270 *     .    aggressive early deflation using that part of
00271 *     .    the deflation window that converged using INFQR
00272 *     .    here and there to keep track.) ====
00273 *
00274       CALL DLACPY( 'U', JW, JW, H( KWTOP, KWTOP ), LDH, T, LDT )
00275       CALL DCOPY( JW-1, H( KWTOP+1, KWTOP ), LDH+1, T( 2, 1 ), LDT+1 )
00276 *
00277       CALL DLASET( 'A', JW, JW, ZERO, ONE, V, LDV )
00278       NMIN = ILAENV( 12, 'DLAQR3', 'SV', JW, 1, JW, LWORK )
00279       IF( JW.GT.NMIN ) THEN
00280          CALL DLAQR4( .true., .true., JW, 1, JW, T, LDT, SR( KWTOP ),
00281      $                SI( KWTOP ), 1, JW, V, LDV, WORK, LWORK, INFQR )
00282       ELSE
00283          CALL DLAHQR( .true., .true., JW, 1, JW, T, LDT, SR( KWTOP ),
00284      $                SI( KWTOP ), 1, JW, V, LDV, INFQR )
00285       END IF
00286 *
00287 *     ==== DTREXC needs a clean margin near the diagonal ====
00288 *
00289       DO 10 J = 1, JW - 3
00290          T( J+2, J ) = ZERO
00291          T( J+3, J ) = ZERO
00292    10 CONTINUE
00293       IF( JW.GT.2 )
00294      $   T( JW, JW-2 ) = ZERO
00295 *
00296 *     ==== Deflation detection loop ====
00297 *
00298       NS = JW
00299       ILST = INFQR + 1
00300    20 CONTINUE
00301       IF( ILST.LE.NS ) THEN
00302          IF( NS.EQ.1 ) THEN
00303             BULGE = .FALSE.
00304          ELSE
00305             BULGE = T( NS, NS-1 ).NE.ZERO
00306          END IF
00307 *
00308 *        ==== Small spike tip test for deflation ====
00309 *
00310          IF( .NOT.BULGE ) THEN
00311 *
00312 *           ==== Real eigenvalue ====
00313 *
00314             FOO = ABS( T( NS, NS ) )
00315             IF( FOO.EQ.ZERO )
00316      $         FOO = ABS( S )
00317             IF( ABS( S*V( 1, NS ) ).LE.MAX( SMLNUM, ULP*FOO ) ) THEN
00318 *
00319 *              ==== Deflatable ====
00320 *
00321                NS = NS - 1
00322             ELSE
00323 *
00324 *              ==== Undeflatable.   Move it up out of the way.
00325 *              .    (DTREXC can not fail in this case.) ====
00326 *
00327                IFST = NS
00328                CALL DTREXC( 'V', JW, T, LDT, V, LDV, IFST, ILST, WORK,
00329      $                      INFO )
00330                ILST = ILST + 1
00331             END IF
00332          ELSE
00333 *
00334 *           ==== Complex conjugate pair ====
00335 *
00336             FOO = ABS( T( NS, NS ) ) + SQRT( ABS( T( NS, NS-1 ) ) )*
00337      $            SQRT( ABS( T( NS-1, NS ) ) )
00338             IF( FOO.EQ.ZERO )
00339      $         FOO = ABS( S )
00340             IF( MAX( ABS( S*V( 1, NS ) ), ABS( S*V( 1, NS-1 ) ) ).LE.
00341      $          MAX( SMLNUM, ULP*FOO ) ) THEN
00342 *
00343 *              ==== Deflatable ====
00344 *
00345                NS = NS - 2
00346             ELSE
00347 *
00348 *              ==== Undeflatable. Move them up out of the way.
00349 *              .    Fortunately, DTREXC does the right thing with
00350 *              .    ILST in case of a rare exchange failure. ====
00351 *
00352                IFST = NS
00353                CALL DTREXC( 'V', JW, T, LDT, V, LDV, IFST, ILST, WORK,
00354      $                      INFO )
00355                ILST = ILST + 2
00356             END IF
00357          END IF
00358 *
00359 *        ==== End deflation detection loop ====
00360 *
00361          GO TO 20
00362       END IF
00363 *
00364 *        ==== Return to Hessenberg form ====
00365 *
00366       IF( NS.EQ.0 )
00367      $   S = ZERO
00368 *
00369       IF( NS.LT.JW ) THEN
00370 *
00371 *        ==== sorting diagonal blocks of T improves accuracy for
00372 *        .    graded matrices.  Bubble sort deals well with
00373 *        .    exchange failures. ====
00374 *
00375          SORTED = .false.
00376          I = NS + 1
00377    30    CONTINUE
00378          IF( SORTED )
00379      $      GO TO 50
00380          SORTED = .true.
00381 *
00382          KEND = I - 1
00383          I = INFQR + 1
00384          IF( I.EQ.NS ) THEN
00385             K = I + 1
00386          ELSE IF( T( I+1, I ).EQ.ZERO ) THEN
00387             K = I + 1
00388          ELSE
00389             K = I + 2
00390          END IF
00391    40    CONTINUE
00392          IF( K.LE.KEND ) THEN
00393             IF( K.EQ.I+1 ) THEN
00394                EVI = ABS( T( I, I ) )
00395             ELSE
00396                EVI = ABS( T( I, I ) ) + SQRT( ABS( T( I+1, I ) ) )*
00397      $               SQRT( ABS( T( I, I+1 ) ) )
00398             END IF
00399 *
00400             IF( K.EQ.KEND ) THEN
00401                EVK = ABS( T( K, K ) )
00402             ELSE IF( T( K+1, K ).EQ.ZERO ) THEN
00403                EVK = ABS( T( K, K ) )
00404             ELSE
00405                EVK = ABS( T( K, K ) ) + SQRT( ABS( T( K+1, K ) ) )*
00406      $               SQRT( ABS( T( K, K+1 ) ) )
00407             END IF
00408 *
00409             IF( EVI.GE.EVK ) THEN
00410                I = K
00411             ELSE
00412                SORTED = .false.
00413                IFST = I
00414                ILST = K
00415                CALL DTREXC( 'V', JW, T, LDT, V, LDV, IFST, ILST, WORK,
00416      $                      INFO )
00417                IF( INFO.EQ.0 ) THEN
00418                   I = ILST
00419                ELSE
00420                   I = K
00421                END IF
00422             END IF
00423             IF( I.EQ.KEND ) THEN
00424                K = I + 1
00425             ELSE IF( T( I+1, I ).EQ.ZERO ) THEN
00426                K = I + 1
00427             ELSE
00428                K = I + 2
00429             END IF
00430             GO TO 40
00431          END IF
00432          GO TO 30
00433    50    CONTINUE
00434       END IF
00435 *
00436 *     ==== Restore shift/eigenvalue array from T ====
00437 *
00438       I = JW
00439    60 CONTINUE
00440       IF( I.GE.INFQR+1 ) THEN
00441          IF( I.EQ.INFQR+1 ) THEN
00442             SR( KWTOP+I-1 ) = T( I, I )
00443             SI( KWTOP+I-1 ) = ZERO
00444             I = I - 1
00445          ELSE IF( T( I, I-1 ).EQ.ZERO ) THEN
00446             SR( KWTOP+I-1 ) = T( I, I )
00447             SI( KWTOP+I-1 ) = ZERO
00448             I = I - 1
00449          ELSE
00450             AA = T( I-1, I-1 )
00451             CC = T( I, I-1 )
00452             BB = T( I-1, I )
00453             DD = T( I, I )
00454             CALL DLANV2( AA, BB, CC, DD, SR( KWTOP+I-2 ),
00455      $                   SI( KWTOP+I-2 ), SR( KWTOP+I-1 ),
00456      $                   SI( KWTOP+I-1 ), CS, SN )
00457             I = I - 2
00458          END IF
00459          GO TO 60
00460       END IF
00461 *
00462       IF( NS.LT.JW .OR. S.EQ.ZERO ) THEN
00463          IF( NS.GT.1 .AND. S.NE.ZERO ) THEN
00464 *
00465 *           ==== Reflect spike back into lower triangle ====
00466 *
00467             CALL DCOPY( NS, V, LDV, WORK, 1 )
00468             BETA = WORK( 1 )
00469             CALL DLARFG( NS, BETA, WORK( 2 ), 1, TAU )
00470             WORK( 1 ) = ONE
00471 *
00472             CALL DLASET( 'L', JW-2, JW-2, ZERO, ZERO, T( 3, 1 ), LDT )
00473 *
00474             CALL DLARF( 'L', NS, JW, WORK, 1, TAU, T, LDT,
00475      $                  WORK( JW+1 ) )
00476             CALL DLARF( 'R', NS, NS, WORK, 1, TAU, T, LDT,
00477      $                  WORK( JW+1 ) )
00478             CALL DLARF( 'R', JW, NS, WORK, 1, TAU, V, LDV,
00479      $                  WORK( JW+1 ) )
00480 *
00481             CALL DGEHRD( JW, 1, NS, T, LDT, WORK, WORK( JW+1 ),
00482      $                   LWORK-JW, INFO )
00483          END IF
00484 *
00485 *        ==== Copy updated reduced window into place ====
00486 *
00487          IF( KWTOP.GT.1 )
00488      $      H( KWTOP, KWTOP-1 ) = S*V( 1, 1 )
00489          CALL DLACPY( 'U', JW, JW, T, LDT, H( KWTOP, KWTOP ), LDH )
00490          CALL DCOPY( JW-1, T( 2, 1 ), LDT+1, H( KWTOP+1, KWTOP ),
00491      $               LDH+1 )
00492 *
00493 *        ==== Accumulate orthogonal matrix in order update
00494 *        .    H and Z, if requested.  ====
00495 *
00496          IF( NS.GT.1 .AND. S.NE.ZERO )
00497      $      CALL DORMHR( 'R', 'N', JW, NS, 1, NS, T, LDT, WORK, V, LDV,
00498      $                   WORK( JW+1 ), LWORK-JW, INFO )
00499 *
00500 *        ==== Update vertical slab in H ====
00501 *
00502          IF( WANTT ) THEN
00503             LTOP = 1
00504          ELSE
00505             LTOP = KTOP
00506          END IF
00507          DO 70 KROW = LTOP, KWTOP - 1, NV
00508             KLN = MIN( NV, KWTOP-KROW )
00509             CALL DGEMM( 'N', 'N', KLN, JW, JW, ONE, H( KROW, KWTOP ),
00510      $                  LDH, V, LDV, ZERO, WV, LDWV )
00511             CALL DLACPY( 'A', KLN, JW, WV, LDWV, H( KROW, KWTOP ), LDH )
00512    70    CONTINUE
00513 *
00514 *        ==== Update horizontal slab in H ====
00515 *
00516          IF( WANTT ) THEN
00517             DO 80 KCOL = KBOT + 1, N, NH
00518                KLN = MIN( NH, N-KCOL+1 )
00519                CALL DGEMM( 'C', 'N', JW, KLN, JW, ONE, V, LDV,
00520      $                     H( KWTOP, KCOL ), LDH, ZERO, T, LDT )
00521                CALL DLACPY( 'A', JW, KLN, T, LDT, H( KWTOP, KCOL ),
00522      $                      LDH )
00523    80       CONTINUE
00524          END IF
00525 *
00526 *        ==== Update vertical slab in Z ====
00527 *
00528          IF( WANTZ ) THEN
00529             DO 90 KROW = ILOZ, IHIZ, NV
00530                KLN = MIN( NV, IHIZ-KROW+1 )
00531                CALL DGEMM( 'N', 'N', KLN, JW, JW, ONE, Z( KROW, KWTOP ),
00532      $                     LDZ, V, LDV, ZERO, WV, LDWV )
00533                CALL DLACPY( 'A', KLN, JW, WV, LDWV, Z( KROW, KWTOP ),
00534      $                      LDZ )
00535    90       CONTINUE
00536          END IF
00537       END IF
00538 *
00539 *     ==== Return the number of deflations ... ====
00540 *
00541       ND = JW - NS
00542 *
00543 *     ==== ... and the number of shifts. (Subtracting
00544 *     .    INFQR from the spike length takes care
00545 *     .    of the case of a rare QR failure while
00546 *     .    calculating eigenvalues of the deflation
00547 *     .    window.)  ====
00548 *
00549       NS = NS - INFQR
00550 *
00551 *      ==== Return optimal workspace. ====
00552 *
00553       WORK( 1 ) = DBLE( LWKOPT )
00554 *
00555 *     ==== End of DLAQR3 ====
00556 *
00557       END