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- SUBROUTINE DLAQR4( WANTT, WANTZ, N, ILO, IHI, H, LDH, WR, WI,
- $ ILOZ, IHIZ, Z, LDZ, WORK, LWORK, INFO )
-*
-* -- LAPACK auxiliary routine (version 3.1) --
-* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
-* November 2006
-*
-* .. Scalar Arguments ..
- INTEGER IHI, IHIZ, ILO, ILOZ, INFO, LDH, LDZ, LWORK, N
- LOGICAL WANTT, WANTZ
-* ..
-* .. Array Arguments ..
- DOUBLE PRECISION H( LDH, * ), WI( * ), WORK( * ), WR( * ),
- $ Z( LDZ, * )
-* ..
-*
-* This subroutine implements one level of recursion for DLAQR0.
-* It is a complete implementation of the small bulge multi-shift
-* QR algorithm. It may be called by DLAQR0 and, for large enough
-* deflation window size, it may be called by DLAQR3. This
-* subroutine is identical to DLAQR0 except that it calls DLAQR2
-* instead of DLAQR3.
-*
-* Purpose
-* =======
-*
-* DLAQR4 computes the eigenvalues of a Hessenberg matrix H
-* and, optionally, the matrices T and Z from the Schur decomposition
-* H = Z T Z**T, where T is an upper quasi-triangular matrix (the
-* Schur form), and Z is the orthogonal matrix of Schur vectors.
-*
-* Optionally Z may be postmultiplied into an input orthogonal
-* 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 orthogonal matrix Q: A = Q*H*Q**T = (QZ)*T*(QZ)**T.
-*
-* Arguments
-* =========
-*
-* WANTT (input) LOGICAL
-* = .TRUE. : the full Schur form T is required;
-* = .FALSE.: only eigenvalues are required.
-*
-* WANTZ (input) LOGICAL
-* = .TRUE. : the matrix of Schur vectors Z is required;
-* = .FALSE.: Schur vectors are not required.
-*
-* N (input) INTEGER
-* The order of the matrix H. N .GE. 0.
-*
-* ILO (input) INTEGER
-* IHI (input) 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 DGEBAL, and then passed to DGEHRD when the
-* matrix output by DGEBAL 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.
-*
-* H (input/output) DOUBLE PRECISION 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 quasi-triangular matrix T from the Schur
-* decomposition (the Schur form); 2-by-2 diagonal blocks
-* (corresponding to complex conjugate pairs of eigenvalues)
-* are returned in standard form, with H(i,i) = H(i+1,i+1)
-* and H(i+1,i)*H(i,i+1).LT.0. If INFO = 0 and WANTT 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.
-*
-* LDH (input) INTEGER
-* The leading dimension of the array H. LDH .GE. max(1,N).
-*
-* WR (output) DOUBLE PRECISION array, dimension (IHI)
-* WI (output) DOUBLE PRECISION array, dimension (IHI)
-* The real and imaginary parts, respectively, of the computed
-* eigenvalues of H(ILO:IHI,ILO:IHI) are stored WR(ILO:IHI)
-* and WI(ILO:IHI). If two eigenvalues are computed as a
-* complex conjugate pair, they are stored in consecutive
-* elements of WR and WI, say the i-th and (i+1)th, with
-* WI(i) .GT. 0 and WI(i+1) .LT. 0. 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
-* WR(i) = H(i,i) and, if H(i:i+1,i:i+1) is a 2-by-2 diagonal
-* block, WI(i) = sqrt(-H(i+1,i)*H(i,i+1)) and
-* WI(i+1) = -WI(i).
-*
-* ILOZ (input) INTEGER
-* IHIZ (input) 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.
-*
-* Z (input/output) DOUBLE PRECISION 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.)
-*
-* LDZ (input) INTEGER
-* The leading dimension of the array Z. if WANTZ is .TRUE.
-* then LDZ.GE.MAX(1,IHIZ). Otherwize, LDZ.GE.1.
-*
-* WORK (workspace/output) DOUBLE PRECISION array, dimension LWORK
-* On exit, if LWORK = -1, WORK(1) returns an estimate of
-* the optimal value for LWORK.
-*
-* LWORK (input) 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 DLAQR4 does a workspace query.
-* In this case, DLAQR4 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.
-*
-*
-* INFO (output) INTEGER
-* = 0: successful exit
-* .GT. 0: if INFO = i, DLAQR4 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 an orthogonal matrix. The final
-* value of H is upper Hessenberg and quasi-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 orthogonal matrix in (*) (regard-
-* less of the value of WANTT.)
-*
-* If INFO .GT. 0 and WANTZ is .FALSE., then Z is not
-* accessed.
-*
-* ================================================================
-* Based on contributions by
-* 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.
-*
-* ================================================================
-* .. Parameters ..
-*
-* ==== Matrices of order NTINY or smaller must be processed by
-* . DLAHQR because of insufficient subdiagonal scratch space.
-* . (This is a hard limit.) ====
-*
-* ==== Exceptional deflation windows: try to cure rare
-* . slow convergence by increasing the size of the
-* . deflation window after KEXNW iterations. =====
-*
-* ==== Exceptional shifts: try to cure rare slow convergence
-* . with ad-hoc exceptional shifts every KEXSH iterations.
-* . The constants WILK1 and WILK2 are used to form the
-* . exceptional shifts. ====
-*
- INTEGER NTINY
- PARAMETER ( NTINY = 11 )
- INTEGER KEXNW, KEXSH
- PARAMETER ( KEXNW = 5, KEXSH = 6 )
- DOUBLE PRECISION WILK1, WILK2
- PARAMETER ( WILK1 = 0.75d0, WILK2 = -0.4375d0 )
- DOUBLE PRECISION ZERO, ONE
- PARAMETER ( ZERO = 0.0d0, ONE = 1.0d0 )
-* ..
-* .. Local Scalars ..
- DOUBLE PRECISION AA, BB, CC, CS, DD, SN, SS, SWAP
- INTEGER I, INF, IT, ITMAX, K, KACC22, KBOT, KDU, KS,
- $ KT, KTOP, KU, KV, KWH, KWTOP, KWV, LD, LS,
- $ LWKOPT, NDFL, NH, NHO, NIBBLE, NMIN, NS, NSMAX,
- $ NSR, NVE, NW, NWMAX, NWR
- LOGICAL NWINC, SORTED
- CHARACTER JBCMPZ*2
-* ..
-* .. External Functions ..
- INTEGER ILAENV
- EXTERNAL ILAENV
-* ..
-* .. Local Arrays ..
- DOUBLE PRECISION ZDUM( 1, 1 )
-* ..
-* .. External Subroutines ..
- EXTERNAL DLACPY, DLAHQR, DLANV2, DLAQR2, DLAQR5
-* ..
-* .. Intrinsic Functions ..
- INTRINSIC ABS, DBLE, INT, MAX, MIN, MOD
-* ..
-* .. Executable Statements ..
- INFO = 0
-*
-* ==== Quick return for N = 0: nothing to do. ====
-*
- IF( N.EQ.0 ) THEN
- WORK( 1 ) = ONE
- RETURN
- END IF
-*
-* ==== Set up job flags for ILAENV. ====
-*
- IF( WANTT ) THEN
- JBCMPZ( 1: 1 ) = 'S'
- ELSE
- JBCMPZ( 1: 1 ) = 'E'
- END IF
- IF( WANTZ ) THEN
- JBCMPZ( 2: 2 ) = 'V'
- ELSE
- JBCMPZ( 2: 2 ) = 'N'
- END IF
-*
-* ==== Tiny matrices must use DLAHQR. ====
-*
- IF( N.LE.NTINY ) THEN
-*
-* ==== Estimate optimal workspace. ====
-*
- LWKOPT = 1
- IF( LWORK.NE.-1 )
- $ CALL DLAHQR( WANTT, WANTZ, N, ILO, IHI, H, LDH, WR, WI,
- $ ILOZ, IHIZ, Z, LDZ, INFO )
- ELSE
-*
-* ==== Use small bulge multi-shift QR with aggressive early
-* . deflation on larger-than-tiny matrices. ====
-*
-* ==== Hope for the best. ====
-*
- INFO = 0
-*
-* ==== NWR = recommended deflation window size. At this
-* . point, N .GT. NTINY = 11, so there is enough
-* . subdiagonal workspace for NWR.GE.2 as required.
-* . (In fact, there is enough subdiagonal space for
-* . NWR.GE.3.) ====
-*
- NWR = ILAENV( 13, 'DLAQR4', JBCMPZ, N, ILO, IHI, LWORK )
- NWR = MAX( 2, NWR )
- NWR = MIN( IHI-ILO+1, ( N-1 ) / 3, NWR )
- NW = NWR
-*
-* ==== NSR = recommended number of simultaneous shifts.
-* . At this point N .GT. NTINY = 11, so there is at
-* . enough subdiagonal workspace for NSR to be even
-* . and greater than or equal to two as required. ====
-*
- NSR = ILAENV( 15, 'DLAQR4', JBCMPZ, N, ILO, IHI, LWORK )
- NSR = MIN( NSR, ( N+6 ) / 9, IHI-ILO )
- NSR = MAX( 2, NSR-MOD( NSR, 2 ) )
-*
-* ==== Estimate optimal workspace ====
-*
-* ==== Workspace query call to DLAQR2 ====
-*
- CALL DLAQR2( WANTT, WANTZ, N, ILO, IHI, NWR+1, H, LDH, ILOZ,
- $ IHIZ, Z, LDZ, LS, LD, WR, WI, H, LDH, N, H, LDH,
- $ N, H, LDH, WORK, -1 )
-*
-* ==== Optimal workspace = MAX(DLAQR5, DLAQR2) ====
-*
- LWKOPT = MAX( 3*NSR / 2, INT( WORK( 1 ) ) )
-*
-* ==== Quick return in case of workspace query. ====
-*
- IF( LWORK.EQ.-1 ) THEN
- WORK( 1 ) = DBLE( LWKOPT )
- RETURN
- END IF
-*
-* ==== DLAHQR/DLAQR0 crossover point ====
-*
- NMIN = ILAENV( 12, 'DLAQR4', JBCMPZ, N, ILO, IHI, LWORK )
- NMIN = MAX( NTINY, NMIN )
-*
-* ==== Nibble crossover point ====
-*
- NIBBLE = ILAENV( 14, 'DLAQR4', JBCMPZ, N, ILO, IHI, LWORK )
- NIBBLE = MAX( 0, NIBBLE )
-*
-* ==== Accumulate reflections during ttswp? Use block
-* . 2-by-2 structure during matrix-matrix multiply? ====
-*
- KACC22 = ILAENV( 16, 'DLAQR4', JBCMPZ, N, ILO, IHI, LWORK )
- KACC22 = MAX( 0, KACC22 )
- KACC22 = MIN( 2, KACC22 )
-*
-* ==== NWMAX = the largest possible deflation window for
-* . which there is sufficient workspace. ====
-*
- NWMAX = MIN( ( N-1 ) / 3, LWORK / 2 )
-*
-* ==== NSMAX = the Largest number of simultaneous shifts
-* . for which there is sufficient workspace. ====
-*
- NSMAX = MIN( ( N+6 ) / 9, 2*LWORK / 3 )
- NSMAX = NSMAX - MOD( NSMAX, 2 )
-*
-* ==== NDFL: an iteration count restarted at deflation. ====
-*
- NDFL = 1
-*
-* ==== ITMAX = iteration limit ====
-*
- ITMAX = MAX( 30, 2*KEXSH )*MAX( 10, ( IHI-ILO+1 ) )
-*
-* ==== Last row and column in the active block ====
-*
- KBOT = IHI
-*
-* ==== Main Loop ====
-*
- DO 80 IT = 1, ITMAX
-*
-* ==== Done when KBOT falls below ILO ====
-*
- IF( KBOT.LT.ILO )
- $ GO TO 90
-*
-* ==== Locate active block ====
-*
- DO 10 K = KBOT, ILO + 1, -1
- IF( H( K, K-1 ).EQ.ZERO )
- $ GO TO 20
- 10 CONTINUE
- K = ILO
- 20 CONTINUE
- KTOP = K
-*
-* ==== Select deflation window size ====
-*
- NH = KBOT - KTOP + 1
- IF( NDFL.LT.KEXNW .OR. NH.LT.NW ) THEN
-*
-* ==== Typical deflation window. If possible and
-* . advisable, nibble the entire active block.
-* . If not, use size NWR or NWR+1 depending upon
-* . which has the smaller corresponding subdiagonal
-* . entry (a heuristic). ====
-*
- NWINC = .TRUE.
- IF( NH.LE.MIN( NMIN, NWMAX ) ) THEN
- NW = NH
- ELSE
- NW = MIN( NWR, NH, NWMAX )
- IF( NW.LT.NWMAX ) THEN
- IF( NW.GE.NH-1 ) THEN
- NW = NH
- ELSE
- KWTOP = KBOT - NW + 1
- IF( ABS( H( KWTOP, KWTOP-1 ) ).GT.
- $ ABS( H( KWTOP-1, KWTOP-2 ) ) )NW = NW + 1
- END IF
- END IF
- END IF
- ELSE
-*
-* ==== Exceptional deflation window. If there have
-* . been no deflations in KEXNW or more iterations,
-* . then vary the deflation window size. At first,
-* . because, larger windows are, in general, more
-* . powerful than smaller ones, rapidly increase the
-* . window up to the maximum reasonable and possible.
-* . Then maybe try a slightly smaller window. ====
-*
- IF( NWINC .AND. NW.LT.MIN( NWMAX, NH ) ) THEN
- NW = MIN( NWMAX, NH, 2*NW )
- ELSE
- NWINC = .FALSE.
- IF( NW.EQ.NH .AND. NH.GT.2 )
- $ NW = NH - 1
- END IF
- END IF
-*
-* ==== Aggressive early deflation:
-* . split workspace under the subdiagonal into
-* . - an nw-by-nw work array V in the lower
-* . left-hand-corner,
-* . - an NW-by-at-least-NW-but-more-is-better
-* . (NW-by-NHO) horizontal work array along
-* . the bottom edge,
-* . - an at-least-NW-but-more-is-better (NHV-by-NW)
-* . vertical work array along the left-hand-edge.
-* . ====
-*
- KV = N - NW + 1
- KT = NW + 1
- NHO = ( N-NW-1 ) - KT + 1
- KWV = NW + 2
- NVE = ( N-NW ) - KWV + 1
-*
-* ==== Aggressive early deflation ====
-*
- CALL DLAQR2( WANTT, WANTZ, N, KTOP, KBOT, NW, H, LDH, ILOZ,
- $ IHIZ, Z, LDZ, LS, LD, WR, WI, H( KV, 1 ), LDH,
- $ NHO, H( KV, KT ), LDH, NVE, H( KWV, 1 ), LDH,
- $ WORK, LWORK )
-*
-* ==== Adjust KBOT accounting for new deflations. ====
-*
- KBOT = KBOT - LD
-*
-* ==== KS points to the shifts. ====
-*
- KS = KBOT - LS + 1
-*
-* ==== Skip an expensive QR sweep if there is a (partly
-* . heuristic) reason to expect that many eigenvalues
-* . will deflate without it. Here, the QR sweep is
-* . skipped if many eigenvalues have just been deflated
-* . or if the remaining active block is small.
-*
- IF( ( LD.EQ.0 ) .OR. ( ( 100*LD.LE.NW*NIBBLE ) .AND. ( KBOT-
- $ KTOP+1.GT.MIN( NMIN, NWMAX ) ) ) ) THEN
-*
-* ==== NS = nominal number of simultaneous shifts.
-* . This may be lowered (slightly) if DLAQR2
-* . did not provide that many shifts. ====
-*
- NS = MIN( NSMAX, NSR, MAX( 2, KBOT-KTOP ) )
- NS = NS - MOD( NS, 2 )
-*
-* ==== If there have been no deflations
-* . in a multiple of KEXSH iterations,
-* . then try exceptional shifts.
-* . Otherwise use shifts provided by
-* . DLAQR2 above or from the eigenvalues
-* . of a trailing principal submatrix. ====
-*
- IF( MOD( NDFL, KEXSH ).EQ.0 ) THEN
- KS = KBOT - NS + 1
- DO 30 I = KBOT, MAX( KS+1, KTOP+2 ), -2
- SS = ABS( H( I, I-1 ) ) + ABS( H( I-1, I-2 ) )
- AA = WILK1*SS + H( I, I )
- BB = SS
- CC = WILK2*SS
- DD = AA
- CALL DLANV2( AA, BB, CC, DD, WR( I-1 ), WI( I-1 ),
- $ WR( I ), WI( I ), CS, SN )
- 30 CONTINUE
- IF( KS.EQ.KTOP ) THEN
- WR( KS+1 ) = H( KS+1, KS+1 )
- WI( KS+1 ) = ZERO
- WR( KS ) = WR( KS+1 )
- WI( KS ) = WI( KS+1 )
- END IF
- ELSE
-*
-* ==== Got NS/2 or fewer shifts? Use DLAHQR
-* . on a trailing principal submatrix to
-* . get more. (Since NS.LE.NSMAX.LE.(N+6)/9,
-* . there is enough space below the subdiagonal
-* . to fit an NS-by-NS scratch array.) ====
-*
- IF( KBOT-KS+1.LE.NS / 2 ) THEN
- KS = KBOT - NS + 1
- KT = N - NS + 1
- CALL DLACPY( 'A', NS, NS, H( KS, KS ), LDH,
- $ H( KT, 1 ), LDH )
- CALL DLAHQR( .false., .false., NS, 1, NS,
- $ H( KT, 1 ), LDH, WR( KS ), WI( KS ),
- $ 1, 1, ZDUM, 1, INF )
- KS = KS + INF
-*
-* ==== In case of a rare QR failure use
-* . eigenvalues of the trailing 2-by-2
-* . principal submatrix. ====
-*
- IF( KS.GE.KBOT ) THEN
- AA = H( KBOT-1, KBOT-1 )
- CC = H( KBOT, KBOT-1 )
- BB = H( KBOT-1, KBOT )
- DD = H( KBOT, KBOT )
- CALL DLANV2( AA, BB, CC, DD, WR( KBOT-1 ),
- $ WI( KBOT-1 ), WR( KBOT ),
- $ WI( KBOT ), CS, SN )
- KS = KBOT - 1
- END IF
- END IF
-*
- IF( KBOT-KS+1.GT.NS ) THEN
-*
-* ==== Sort the shifts (Helps a little)
-* . Bubble sort keeps complex conjugate
-* . pairs together. ====
-*
- SORTED = .false.
- DO 50 K = KBOT, KS + 1, -1
- IF( SORTED )
- $ GO TO 60
- SORTED = .true.
- DO 40 I = KS, K - 1
- IF( ABS( WR( I ) )+ABS( WI( I ) ).LT.
- $ ABS( WR( I+1 ) )+ABS( WI( I+1 ) ) ) THEN
- SORTED = .false.
-*
- SWAP = WR( I )
- WR( I ) = WR( I+1 )
- WR( I+1 ) = SWAP
-*
- SWAP = WI( I )
- WI( I ) = WI( I+1 )
- WI( I+1 ) = SWAP
- END IF
- 40 CONTINUE
- 50 CONTINUE
- 60 CONTINUE
- END IF
-*
-* ==== Shuffle shifts into pairs of real shifts
-* . and pairs of complex conjugate shifts
-* . assuming complex conjugate shifts are
-* . already adjacent to one another. (Yes,
-* . they are.) ====
-*
- DO 70 I = KBOT, KS + 2, -2
- IF( WI( I ).NE.-WI( I-1 ) ) THEN
-*
- SWAP = WR( I )
- WR( I ) = WR( I-1 )
- WR( I-1 ) = WR( I-2 )
- WR( I-2 ) = SWAP
-*
- SWAP = WI( I )
- WI( I ) = WI( I-1 )
- WI( I-1 ) = WI( I-2 )
- WI( I-2 ) = SWAP
- END IF
- 70 CONTINUE
- END IF
-*
-* ==== If there are only two shifts and both are
-* . real, then use only one. ====
-*
- IF( KBOT-KS+1.EQ.2 ) THEN
- IF( WI( KBOT ).EQ.ZERO ) THEN
- IF( ABS( WR( KBOT )-H( KBOT, KBOT ) ).LT.
- $ ABS( WR( KBOT-1 )-H( KBOT, KBOT ) ) ) THEN
- WR( KBOT-1 ) = WR( KBOT )
- ELSE
- WR( KBOT ) = WR( KBOT-1 )
- END IF
- END IF
- END IF
-*
-* ==== Use up to NS of the the smallest magnatiude
-* . shifts. If there aren't NS shifts available,
-* . then use them all, possibly dropping one to
-* . make the number of shifts even. ====
-*
- NS = MIN( NS, KBOT-KS+1 )
- NS = NS - MOD( NS, 2 )
- KS = KBOT - NS + 1
-*
-* ==== Small-bulge multi-shift QR sweep:
-* . split workspace under the subdiagonal into
-* . - a KDU-by-KDU work array U in the lower
-* . left-hand-corner,
-* . - a KDU-by-at-least-KDU-but-more-is-better
-* . (KDU-by-NHo) horizontal work array WH along
-* . the bottom edge,
-* . - and an at-least-KDU-but-more-is-better-by-KDU
-* . (NVE-by-KDU) vertical work WV arrow along
-* . the left-hand-edge. ====
-*
- KDU = 3*NS - 3
- KU = N - KDU + 1
- KWH = KDU + 1
- NHO = ( N-KDU+1-4 ) - ( KDU+1 ) + 1
- KWV = KDU + 4
- NVE = N - KDU - KWV + 1
-*
-* ==== Small-bulge multi-shift QR sweep ====
-*
- CALL DLAQR5( WANTT, WANTZ, KACC22, N, KTOP, KBOT, NS,
- $ WR( KS ), WI( KS ), H, LDH, ILOZ, IHIZ, Z,
- $ LDZ, WORK, 3, H( KU, 1 ), LDH, NVE,
- $ H( KWV, 1 ), LDH, NHO, H( KU, KWH ), LDH )
- END IF
-*
-* ==== Note progress (or the lack of it). ====
-*
- IF( LD.GT.0 ) THEN
- NDFL = 1
- ELSE
- NDFL = NDFL + 1
- END IF
-*
-* ==== End of main loop ====
- 80 CONTINUE
-*
-* ==== Iteration limit exceeded. Set INFO to show where
-* . the problem occurred and exit. ====
-*
- INFO = KBOT
- 90 CONTINUE
- END IF
-*
-* ==== Return the optimal value of LWORK. ====
-*
- WORK( 1 ) = DBLE( LWKOPT )
-*
-* ==== End of DLAQR4 ====
-*
- END