SUBROUTINE SLAQR2( WANTT, WANTZ, N, KTOP, KBOT, NW, H, LDH, ILOZ,
$ IHIZ, Z, LDZ, NS, ND, SR, SI, V, LDV, NH, T,
$ LDT, NV, WV, LDWV, WORK, LWORK )
*
* -- LAPACK auxiliary routine (version 3.1) --
* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
* November 2006
*
* .. Scalar Arguments ..
INTEGER IHIZ, ILOZ, KBOT, KTOP, LDH, LDT, LDV, LDWV,
$ LDZ, LWORK, N, ND, NH, NS, NV, NW
LOGICAL WANTT, WANTZ
* ..
* .. Array Arguments ..
REAL H( LDH, * ), SI( * ), SR( * ), T( LDT, * ),
$ V( LDV, * ), WORK( * ), WV( LDWV, * ),
$ Z( LDZ, * )
* ..
*
* This subroutine is identical to SLAQR3 except that it avoids
* recursion by calling SLAHQR instead of SLAQR4.
*
*
* ******************************************************************
* Aggressive early deflation:
*
* This subroutine accepts as input an upper Hessenberg matrix
* H and performs an orthogonal 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 orthogonal similarity transformation of H. It is to be
* hoped that the final version of H has many zero subdiagonal
* entries.
*
* ******************************************************************
* WANTT (input) LOGICAL
* If .TRUE., then the Hessenberg matrix H is fully updated
* so that the quasi-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.
*
* WANTZ (input) LOGICAL
* If .TRUE., then the orthogonal matrix Z is updated so
* so that the orthogonal Schur factor may be computed
* (in cooperation with the calling subroutine).
* If .FALSE., then Z is not referenced.
*
* N (input) INTEGER
* The order of the matrix H and (if WANTZ is .TRUE.) the
* order of the orthogonal matrix Z.
*
* KTOP (input) 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.
*
* KBOT (input) 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.
*
* NW (input) INTEGER
* Deflation window size. 1 .LE. NW .LE. (KBOT-KTOP+1).
*
* H (input/output) REAL 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 an orthogonal
* similarity transformation, perturbed, and the returned
* to Hessenberg form that (it is to be hoped) has some
* zero subdiagonal entries.
*
* LDH (input) integer
* Leading dimension of H just as declared in the calling
* subroutine. N .LE. LDH
*
* 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. IHIZ .LE. N.
*
* Z (input/output) REAL array, dimension (LDZ,IHI)
* IF WANTZ is .TRUE., then on output, the orthogonal
* similarity transformation mentioned above has been
* accumulated into Z(ILOZ:IHIZ,ILO:IHI) from the right.
* If WANTZ is .FALSE., then Z is unreferenced.
*
* LDZ (input) integer
* The leading dimension of Z just as declared in the
* calling subroutine. 1 .LE. LDZ.
*
* NS (output) integer
* The number of unconverged (ie approximate) eigenvalues
* returned in SR and SI that may be used as shifts by the
* calling subroutine.
*
* ND (output) integer
* The number of converged eigenvalues uncovered by this
* subroutine.
*
* SR (output) REAL array, dimension KBOT
* SI (output) REAL array, dimension KBOT
* On output, the real and imaginary parts of approximate
* eigenvalues that may be used for shifts are stored in
* SR(KBOT-ND-NS+1) through SR(KBOT-ND) and
* SI(KBOT-ND-NS+1) through SI(KBOT-ND), respectively.
* The real and imaginary parts of converged eigenvalues
* are stored in SR(KBOT-ND+1) through SR(KBOT) and
* SI(KBOT-ND+1) through SI(KBOT), respectively.
*
* V (workspace) REAL array, dimension (LDV,NW)
* An NW-by-NW work array.
*
* LDV (input) integer scalar
* The leading dimension of V just as declared in the
* calling subroutine. NW .LE. LDV
*
* NH (input) integer scalar
* The number of columns of T. NH.GE.NW.
*
* T (workspace) REAL array, dimension (LDT,NW)
*
* LDT (input) integer
* The leading dimension of T just as declared in the
* calling subroutine. NW .LE. LDT
*
* NV (input) integer
* The number of rows of work array WV available for
* workspace. NV.GE.NW.
*
* WV (workspace) REAL array, dimension (LDWV,NW)
*
* LDWV (input) integer
* The leading dimension of W just as declared in the
* calling subroutine. NW .LE. LDV
*
* WORK (workspace) REAL 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.
*
* LWORK (input) 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; SLAQR2
* 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.
*
* ================================================================
* Based on contributions by
* Karen Braman and Ralph Byers, Department of Mathematics,
* University of Kansas, USA
*
* ==================================================================
* .. Parameters ..
REAL ZERO, ONE
PARAMETER ( ZERO = 0.0e0, ONE = 1.0e0 )
* ..
* .. Local Scalars ..
REAL AA, BB, BETA, CC, CS, DD, EVI, EVK, FOO, S,
$ SAFMAX, SAFMIN, SMLNUM, SN, TAU, ULP
INTEGER I, IFST, ILST, INFO, INFQR, J, JW, K, KCOL,
$ KEND, KLN, KROW, KWTOP, LTOP, LWK1, LWK2,
$ LWKOPT
LOGICAL BULGE, SORTED
* ..
* .. External Functions ..
REAL SLAMCH
EXTERNAL SLAMCH
* ..
* .. External Subroutines ..
EXTERNAL SCOPY, SGEHRD, SGEMM, SLABAD, SLACPY, SLAHQR,
$ SLANV2, SLARF, SLARFG, SLASET, SORGHR, STREXC
* ..
* .. Intrinsic Functions ..
INTRINSIC ABS, INT, MAX, MIN, REAL, SQRT
* ..
* .. Executable Statements ..
*
* ==== Estimate optimal workspace. ====
*
JW = MIN( NW, KBOT-KTOP+1 )
IF( JW.LE.2 ) THEN
LWKOPT = 1
ELSE
*
* ==== Workspace query call to SGEHRD ====
*
CALL SGEHRD( JW, 1, JW-1, T, LDT, WORK, WORK, -1, INFO )
LWK1 = INT( WORK( 1 ) )
*
* ==== Workspace query call to SORGHR ====
*
CALL SORGHR( JW, 1, JW-1, T, LDT, WORK, WORK, -1, INFO )
LWK2 = INT( WORK( 1 ) )
*
* ==== Optimal workspace ====
*
LWKOPT = JW + MAX( LWK1, LWK2 )
END IF
*
* ==== Quick return in case of workspace query. ====
*
IF( LWORK.EQ.-1 ) THEN
WORK( 1 ) = REAL( LWKOPT )
RETURN
END IF
*
* ==== Nothing to do ...
* ... for an empty active block ... ====
NS = 0
ND = 0
IF( KTOP.GT.KBOT )
$ RETURN
* ... nor for an empty deflation window. ====
IF( NW.LT.1 )
$ RETURN
*
* ==== Machine constants ====
*
SAFMIN = SLAMCH( 'SAFE MINIMUM' )
SAFMAX = ONE / SAFMIN
CALL SLABAD( SAFMIN, SAFMAX )
ULP = SLAMCH( 'PRECISION' )
SMLNUM = SAFMIN*( REAL( N ) / ULP )
*
* ==== Setup deflation window ====
*
JW = MIN( NW, KBOT-KTOP+1 )
KWTOP = KBOT - JW + 1
IF( KWTOP.EQ.KTOP ) THEN
S = ZERO
ELSE
S = H( KWTOP, KWTOP-1 )
END IF
*
IF( KBOT.EQ.KWTOP ) THEN
*
* ==== 1-by-1 deflation window: not much to do ====
*
SR( KWTOP ) = H( KWTOP, KWTOP )
SI( KWTOP ) = ZERO
NS = 1
ND = 0
IF( ABS( S ).LE.MAX( SMLNUM, ULP*ABS( H( KWTOP, KWTOP ) ) ) )
$ THEN
NS = 0
ND = 1
IF( KWTOP.GT.KTOP )
$ H( KWTOP, KWTOP-1 ) = ZERO
END IF
RETURN
END IF
*
* ==== Convert to spike-triangular form. (In case of a
* . rare QR failure, this routine continues to do
* . aggressive early deflation using that part of
* . the deflation window that converged using INFQR
* . here and there to keep track.) ====
*
CALL SLACPY( 'U', JW, JW, H( KWTOP, KWTOP ), LDH, T, LDT )
CALL SCOPY( JW-1, H( KWTOP+1, KWTOP ), LDH+1, T( 2, 1 ), LDT+1 )
*
CALL SLASET( 'A', JW, JW, ZERO, ONE, V, LDV )
CALL SLAHQR( .true., .true., JW, 1, JW, T, LDT, SR( KWTOP ),
$ SI( KWTOP ), 1, JW, V, LDV, INFQR )
*
* ==== STREXC needs a clean margin near the diagonal ====
*
DO 10 J = 1, JW - 3
T( J+2, J ) = ZERO
T( J+3, J ) = ZERO
10 CONTINUE
IF( JW.GT.2 )
$ T( JW, JW-2 ) = ZERO
*
* ==== Deflation detection loop ====
*
NS = JW
ILST = INFQR + 1
20 CONTINUE
IF( ILST.LE.NS ) THEN
IF( NS.EQ.1 ) THEN
BULGE = .FALSE.
ELSE
BULGE = T( NS, NS-1 ).NE.ZERO
END IF
*
* ==== Small spike tip test for deflation ====
*
IF( .NOT.BULGE ) THEN
*
* ==== Real eigenvalue ====
*
FOO = ABS( T( NS, NS ) )
IF( FOO.EQ.ZERO )
$ FOO = ABS( S )
IF( ABS( S*V( 1, NS ) ).LE.MAX( SMLNUM, ULP*FOO ) ) THEN
*
* ==== Deflatable ====
*
NS = NS - 1
ELSE
*
* ==== Undeflatable. Move it up out of the way.
* . (STREXC can not fail in this case.) ====
*
IFST = NS
CALL STREXC( 'V', JW, T, LDT, V, LDV, IFST, ILST, WORK,
$ INFO )
ILST = ILST + 1
END IF
ELSE
*
* ==== Complex conjugate pair ====
*
FOO = ABS( T( NS, NS ) ) + SQRT( ABS( T( NS, NS-1 ) ) )*
$ SQRT( ABS( T( NS-1, NS ) ) )
IF( FOO.EQ.ZERO )
$ FOO = ABS( S )
IF( MAX( ABS( S*V( 1, NS ) ), ABS( S*V( 1, NS-1 ) ) ).LE.
$ MAX( SMLNUM, ULP*FOO ) ) THEN
*
* ==== Deflatable ====
*
NS = NS - 2
ELSE
*
* ==== Undflatable. Move them up out of the way.
* . Fortunately, STREXC does the right thing with
* . ILST in case of a rare exchange failure. ====
*
IFST = NS
CALL STREXC( 'V', JW, T, LDT, V, LDV, IFST, ILST, WORK,
$ INFO )
ILST = ILST + 2
END IF
END IF
*
* ==== End deflation detection loop ====
*
GO TO 20
END IF
*
* ==== Return to Hessenberg form ====
*
IF( NS.EQ.0 )
$ S = ZERO
*
IF( NS.LT.JW ) THEN
*
* ==== sorting diagonal blocks of T improves accuracy for
* . graded matrices. Bubble sort deals well with
* . exchange failures. ====
*
SORTED = .false.
I = NS + 1
30 CONTINUE
IF( SORTED )
$ GO TO 50
SORTED = .true.
*
KEND = I - 1
I = INFQR + 1
IF( I.EQ.NS ) THEN
K = I + 1
ELSE IF( T( I+1, I ).EQ.ZERO ) THEN
K = I + 1
ELSE
K = I + 2
END IF
40 CONTINUE
IF( K.LE.KEND ) THEN
IF( K.EQ.I+1 ) THEN
EVI = ABS( T( I, I ) )
ELSE
EVI = ABS( T( I, I ) ) + SQRT( ABS( T( I+1, I ) ) )*
$ SQRT( ABS( T( I, I+1 ) ) )
END IF
*
IF( K.EQ.KEND ) THEN
EVK = ABS( T( K, K ) )
ELSE IF( T( K+1, K ).EQ.ZERO ) THEN
EVK = ABS( T( K, K ) )
ELSE
EVK = ABS( T( K, K ) ) + SQRT( ABS( T( K+1, K ) ) )*
$ SQRT( ABS( T( K, K+1 ) ) )
END IF
*
IF( EVI.GE.EVK ) THEN
I = K
ELSE
SORTED = .false.
IFST = I
ILST = K
CALL STREXC( 'V', JW, T, LDT, V, LDV, IFST, ILST, WORK,
$ INFO )
IF( INFO.EQ.0 ) THEN
I = ILST
ELSE
I = K
END IF
END IF
IF( I.EQ.KEND ) THEN
K = I + 1
ELSE IF( T( I+1, I ).EQ.ZERO ) THEN
K = I + 1
ELSE
K = I + 2
END IF
GO TO 40
END IF
GO TO 30
50 CONTINUE
END IF
*
* ==== Restore shift/eigenvalue array from T ====
*
I = JW
60 CONTINUE
IF( I.GE.INFQR+1 ) THEN
IF( I.EQ.INFQR+1 ) THEN
SR( KWTOP+I-1 ) = T( I, I )
SI( KWTOP+I-1 ) = ZERO
I = I - 1
ELSE IF( T( I, I-1 ).EQ.ZERO ) THEN
SR( KWTOP+I-1 ) = T( I, I )
SI( KWTOP+I-1 ) = ZERO
I = I - 1
ELSE
AA = T( I-1, I-1 )
CC = T( I, I-1 )
BB = T( I-1, I )
DD = T( I, I )
CALL SLANV2( AA, BB, CC, DD, SR( KWTOP+I-2 ),
$ SI( KWTOP+I-2 ), SR( KWTOP+I-1 ),
$ SI( KWTOP+I-1 ), CS, SN )
I = I - 2
END IF
GO TO 60
END IF
*
IF( NS.LT.JW .OR. S.EQ.ZERO ) THEN
IF( NS.GT.1 .AND. S.NE.ZERO ) THEN
*
* ==== Reflect spike back into lower triangle ====
*
CALL SCOPY( NS, V, LDV, WORK, 1 )
BETA = WORK( 1 )
CALL SLARFG( NS, BETA, WORK( 2 ), 1, TAU )
WORK( 1 ) = ONE
*
CALL SLASET( 'L', JW-2, JW-2, ZERO, ZERO, T( 3, 1 ), LDT )
*
CALL SLARF( 'L', NS, JW, WORK, 1, TAU, T, LDT,
$ WORK( JW+1 ) )
CALL SLARF( 'R', NS, NS, WORK, 1, TAU, T, LDT,
$ WORK( JW+1 ) )
CALL SLARF( 'R', JW, NS, WORK, 1, TAU, V, LDV,
$ WORK( JW+1 ) )
*
CALL SGEHRD( JW, 1, NS, T, LDT, WORK, WORK( JW+1 ),
$ LWORK-JW, INFO )
END IF
*
* ==== Copy updated reduced window into place ====
*
IF( KWTOP.GT.1 )
$ H( KWTOP, KWTOP-1 ) = S*V( 1, 1 )
CALL SLACPY( 'U', JW, JW, T, LDT, H( KWTOP, KWTOP ), LDH )
CALL SCOPY( JW-1, T( 2, 1 ), LDT+1, H( KWTOP+1, KWTOP ),
$ LDH+1 )
*
* ==== Accumulate orthogonal matrix in order update
* . H and Z, if requested. (A modified version
* . of SORGHR that accumulates block Householder
* . transformations into V directly might be
* . marginally more efficient than the following.) ====
*
IF( NS.GT.1 .AND. S.NE.ZERO ) THEN
CALL SORGHR( JW, 1, NS, T, LDT, WORK, WORK( JW+1 ),
$ LWORK-JW, INFO )
CALL SGEMM( 'N', 'N', JW, NS, NS, ONE, V, LDV, T, LDT, ZERO,
$ WV, LDWV )
CALL SLACPY( 'A', JW, NS, WV, LDWV, V, LDV )
END IF
*
* ==== Update vertical slab in H ====
*
IF( WANTT ) THEN
LTOP = 1
ELSE
LTOP = KTOP
END IF
DO 70 KROW = LTOP, KWTOP - 1, NV
KLN = MIN( NV, KWTOP-KROW )
CALL SGEMM( 'N', 'N', KLN, JW, JW, ONE, H( KROW, KWTOP ),
$ LDH, V, LDV, ZERO, WV, LDWV )
CALL SLACPY( 'A', KLN, JW, WV, LDWV, H( KROW, KWTOP ), LDH )
70 CONTINUE
*
* ==== Update horizontal slab in H ====
*
IF( WANTT ) THEN
DO 80 KCOL = KBOT + 1, N, NH
KLN = MIN( NH, N-KCOL+1 )
CALL SGEMM( 'C', 'N', JW, KLN, JW, ONE, V, LDV,
$ H( KWTOP, KCOL ), LDH, ZERO, T, LDT )
CALL SLACPY( 'A', JW, KLN, T, LDT, H( KWTOP, KCOL ),
$ LDH )
80 CONTINUE
END IF
*
* ==== Update vertical slab in Z ====
*
IF( WANTZ ) THEN
DO 90 KROW = ILOZ, IHIZ, NV
KLN = MIN( NV, IHIZ-KROW+1 )
CALL SGEMM( 'N', 'N', KLN, JW, JW, ONE, Z( KROW, KWTOP ),
$ LDZ, V, LDV, ZERO, WV, LDWV )
CALL SLACPY( 'A', KLN, JW, WV, LDWV, Z( KROW, KWTOP ),
$ LDZ )
90 CONTINUE
END IF
END IF
*
* ==== Return the number of deflations ... ====
*
ND = JW - NS
*
* ==== ... and the number of shifts. (Subtracting
* . INFQR from the spike length takes care
* . of the case of a rare QR failure while
* . calculating eigenvalues of the deflation
* . window.) ====
*
NS = NS - INFQR
*
* ==== Return optimal workspace. ====
*
WORK( 1 ) = REAL( LWKOPT )
*
* ==== End of SLAQR2 ====
*
END