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SUBROUTINE MB04QB( TRANC, TRAND, TRANQ, STOREV, STOREW, M, N, K,
$ V, LDV, W, LDW, C, LDC, D, LDD, CS, TAU, DWORK,
$ LDWORK, INFO )
C
C SLICOT RELEASE 5.0.
C
C Copyright (c) 2002-2009 NICONET e.V.
C
C This program is free software: you can redistribute it and/or
C modify it under the terms of the GNU General Public License as
C published by the Free Software Foundation, either version 2 of
C the License, or (at your option) any later version.
C
C This program is distributed in the hope that it will be useful,
C but WITHOUT ANY WARRANTY; without even the implied warranty of
C MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
C GNU General Public License for more details.
C
C You should have received a copy of the GNU General Public License
C along with this program. If not, see
C <http://www.gnu.org/licenses/>.
C
C PURPOSE
C
C To overwrite general real m-by-n matrices C and D, or their
C transposes, with
C
C [ op(C) ]
C Q * [ ] if TRANQ = 'N', or
C [ op(D) ]
C
C T [ op(C) ]
C Q * [ ] if TRANQ = 'T',
C [ op(D) ]
C
C where Q is defined as the product of symplectic reflectors and
C Givens rotators,
C
C Q = diag( H(1),H(1) ) G(1) diag( F(1),F(1) )
C diag( H(2),H(2) ) G(2) diag( F(2),F(2) )
C ....
C diag( H(k),H(k) ) G(k) diag( F(k),F(k) ).
C
C Blocked version.
C
C ARGUMENTS
C
C Mode Parameters
C
C TRANC CHARACTER*1
C Specifies the form of op( C ) as follows:
C = 'N': op( C ) = C;
C = 'T': op( C ) = C';
C = 'C': op( C ) = C'.
C
C TRAND CHARACTER*1
C Specifies the form of op( D ) as follows:
C = 'N': op( D ) = D;
C = 'T': op( D ) = D';
C = 'C': op( D ) = D'.
C
C TRANQ CHARACTER*1
C = 'N': apply Q;
C = 'T': apply Q'.
C
C STOREV CHARACTER*1
C Specifies how the vectors which define the concatenated
C Householder reflectors contained in V are stored:
C = 'C': columnwise;
C = 'R': rowwise.
C
C STOREW CHARACTER*1
C Specifies how the vectors which define the concatenated
C Householder reflectors contained in W are stored:
C = 'C': columnwise;
C = 'R': rowwise.
C
C Input/Output Parameters
C
C M (input) INTEGER
C The number of rows of the matrices op(C) and op(D).
C M >= 0.
C
C N (input) INTEGER
C The number of columns of the matrices op(C) and op(D).
C N >= 0.
C
C K (input) INTEGER
C The number of elementary reflectors whose product defines
C the matrix Q. M >= K >= 0.
C
C V (input) DOUBLE PRECISION array, dimension
C (LDV,K) if STOREV = 'C',
C (LDV,M) if STOREV = 'R'
C On entry with STOREV = 'C', the leading M-by-K part of
C this array must contain in its columns the vectors which
C define the elementary reflectors F(i).
C On entry with STOREV = 'R', the leading K-by-M part of
C this array must contain in its rows the vectors which
C define the elementary reflectors F(i).
C
C LDV INTEGER
C The leading dimension of the array V.
C LDV >= MAX(1,M), if STOREV = 'C';
C LDV >= MAX(1,K), if STOREV = 'R'.
C
C W (input) DOUBLE PRECISION array, dimension
C (LDW,K) if STOREW = 'C',
C (LDW,M) if STOREW = 'R'
C On entry with STOREW = 'C', the leading M-by-K part of
C this array must contain in its columns the vectors which
C define the elementary reflectors H(i).
C On entry with STOREW = 'R', the leading K-by-M part of
C this array must contain in its rows the vectors which
C define the elementary reflectors H(i).
C
C LDW INTEGER
C The leading dimension of the array W.
C LDW >= MAX(1,M), if STOREW = 'C';
C LDW >= MAX(1,K), if STOREW = 'R'.
C
C C (input/output) DOUBLE PRECISION array, dimension
C (LDC,N) if TRANC = 'N',
C (LDC,M) if TRANC = 'T' or TRANC = 'C'
C On entry with TRANC = 'N', the leading M-by-N part of
C this array must contain the matrix C.
C On entry with TRANC = 'C' or TRANC = 'T', the leading
C N-by-M part of this array must contain the transpose of
C the matrix C.
C On exit with TRANC = 'N', the leading M-by-N part of
C this array contains the updated matrix C.
C On exit with TRANC = 'C' or TRANC = 'T', the leading
C N-by-M part of this array contains the transpose of the
C updated matrix C.
C
C LDC INTEGER
C The leading dimension of the array C.
C LDC >= MAX(1,M), if TRANC = 'N';
C LDC >= MAX(1,N), if TRANC = 'T' or TRANC = 'C'.
C
C D (input/output) DOUBLE PRECISION array, dimension
C (LDD,N) if TRAND = 'N',
C (LDD,M) if TRAND = 'T' or TRAND = 'C'
C On entry with TRAND = 'N', the leading M-by-N part of
C this array must contain the matrix D.
C On entry with TRAND = 'C' or TRAND = 'T', the leading
C N-by-M part of this array must contain the transpose of
C the matrix D.
C On exit with TRAND = 'N', the leading M-by-N part of
C this array contains the updated matrix D.
C On exit with TRAND = 'C' or TRAND = 'T', the leading
C N-by-M part of this array contains the transpose of the
C updated matrix D.
C
C LDD INTEGER
C The leading dimension of the array D.
C LDD >= MAX(1,M), if TRAND = 'N';
C LDD >= MAX(1,N), if TRAND = 'T' or TRAND = 'C'.
C
C CS (input) DOUBLE PRECISION array, dimension (2*K)
C On entry, the first 2*K elements of this array must
C contain the cosines and sines of the symplectic Givens
C rotators G(i).
C
C TAU (input) DOUBLE PRECISION array, dimension (K)
C On entry, the first K elements of this array must
C contain the scalar factors of the elementary reflectors
C F(i).
C
C Workspace
C
C DWORK DOUBLE PRECISION array, dimension (LDWORK)
C On exit, if INFO = 0, DWORK(1) returns the optimal
C value of LDWORK.
C On exit, if INFO = -20, DWORK(1) returns the minimum
C value of LDWORK.
C
C LDWORK INTEGER
C The length of the array DWORK. LDWORK >= MAX(1,N).
C
C Error Indicator
C
C INFO INTEGER
C = 0: successful exit;
C < 0: if INFO = -i, the i-th argument had an illegal
C value.
C
C REFERENCES
C
C [1] Kressner, D.
C Block algorithms for orthogonal symplectic factorizations.
C BIT, 43 (4), pp. 775-790, 2003.
C
C CONTRIBUTORS
C
C D. Kressner, Technical Univ. Berlin, Germany, and
C P. Benner, Technical Univ. Chemnitz, Germany, December 2003.
C
C REVISIONS
C
C V. Sima, June 2008 (SLICOT version of the HAPACK routine DOSMSB).
C
C KEYWORDS
C
C Elementary matrix operations, orthogonal symplectic matrix.
C
C ******************************************************************
C
C .. Parameters ..
DOUBLE PRECISION ONE
PARAMETER ( ONE = 1.0D+0 )
C .. Scalar Arguments ..
CHARACTER STOREV, STOREW, TRANC, TRAND, TRANQ
INTEGER INFO, K, LDC, LDD, LDV, LDW, LDWORK, M, N
C .. Array Arguments ..
DOUBLE PRECISION C(LDC,*), CS(*), D(LDD,*), DWORK(*), TAU(*),
$ V(LDV,*), W(LDW,*)
C .. Local Scalars ..
LOGICAL LCOLV, LCOLW, LTRC, LTRD, LTRQ
INTEGER I, IB, IC, ID, IERR, JC, JD, KI, KK, NB, NBMIN,
$ NX, PDRS, PDT, PDW, WRKOPT
C .. External Functions ..
INTEGER UE01MD
LOGICAL LSAME
EXTERNAL LSAME, UE01MD
C .. External Subroutines ..
EXTERNAL MB04QC, MB04QF, MB04QU, XERBLA
C .. Intrinsic Functions ..
INTRINSIC DBLE, INT, MAX, MIN, SQRT
C
C .. Executable Statements ..
C
C Decode the scalar input parameters.
C
INFO = 0
LCOLV = LSAME( STOREV, 'C' )
LCOLW = LSAME( STOREW, 'C' )
LTRC = LSAME( TRANC, 'T' ) .OR. LSAME( TRANC, 'C' )
LTRD = LSAME( TRAND, 'T' ) .OR. LSAME( TRAND, 'C' )
LTRQ = LSAME( TRANQ, 'T' )
C
C Check the scalar input parameters.
C
IF ( .NOT.( LTRC .OR. LSAME( TRANC, 'N' ) ) ) THEN
INFO = -1
ELSE IF ( .NOT.( LTRD .OR. LSAME( TRAND, 'N' ) ) ) THEN
INFO = -2
ELSE IF ( .NOT.( LTRQ .OR. LSAME( TRANQ, 'N' ) ) ) THEN
INFO = -3
ELSE IF ( .NOT.( LCOLV .OR. LSAME( STOREV, 'R' ) ) ) THEN
INFO = -4
ELSE IF ( .NOT.( LCOLW .OR. LSAME( STOREW, 'R' ) ) ) THEN
INFO = -5
ELSE IF ( M.LT.0 ) THEN
INFO = -6
ELSE IF ( N.LT.0 ) THEN
INFO = -7
ELSE IF ( K.LT.0 .OR. K.GT.M ) THEN
INFO = -8
ELSE IF ( ( LCOLV .AND. LDV.LT.MAX( 1, M ) ) .OR.
$ ( .NOT.LCOLV .AND. LDV.LT.MAX( 1, K ) ) ) THEN
INFO = -10
ELSE IF ( ( LCOLW .AND. LDW.LT.MAX( 1, M ) ) .OR.
$ ( .NOT.LCOLW .AND. LDW.LT.MAX( 1, K ) ) ) THEN
INFO = -12
ELSE IF ( ( LTRC .AND. LDC.LT.MAX( 1, N ) ) .OR.
$ ( .NOT.LTRC .AND. LDC.LT.MAX( 1, M ) ) ) THEN
INFO = -14
ELSE IF ( ( LTRD .AND. LDD.LT.MAX( 1, N ) ) .OR.
$ ( .NOT.LTRD .AND. LDD.LT.MAX( 1, M ) ) ) THEN
INFO = -16
ELSE IF ( LDWORK.LT.MAX( 1, N ) ) THEN
DWORK(1) = DBLE( MAX( 1, N ) )
INFO = -20
END IF
C
C Return if there were illegal values.
C
IF ( INFO.NE.0 ) THEN
CALL XERBLA( 'MB04QB', -INFO )
RETURN
END IF
C
C Quick return if possible.
C
IF ( MIN( K, M, N ).EQ.0 ) THEN
DWORK(1) = ONE
RETURN
END IF
C
NBMIN = 2
NX = 0
WRKOPT = N
NB = UE01MD( 1, 'MB04QB', TRANC // TRAND // TRANQ, M, N, K )
IF ( NB.GT.1 .AND. NB.LT.K ) THEN
C
C Determine when to cross over from blocked to unblocked code.
C
NX = MAX( 0, UE01MD( 3, 'MB04QB', TRANC // TRAND // TRANQ, M,
$ N, K ) )
IF ( NX.LT.K ) THEN
C
C Determine if workspace is large enough for blocked code.
C
WRKOPT = MAX( WRKOPT, 9*N*NB + 15*NB*NB )
IF ( LDWORK.LT.WRKOPT ) THEN
C
C Not enough workspace to use optimal NB: reduce NB and
C determine the minimum value of NB.
C
NB = INT( ( SQRT( DBLE( 81*N*N + 60*LDWORK ) )
$ - DBLE( 9*N ) ) / 30.0D0 )
NBMIN = MAX( 2, UE01MD( 2, 'MB04QB', TRANC // TRAND //
$ TRANQ, M, N, K ) )
END IF
END IF
END IF
C
PDRS = 1
PDT = PDRS + 6*NB*NB
PDW = PDT + 9*NB*NB
IC = 1
JC = 1
ID = 1
JD = 1
C
IF ( LTRQ ) THEN
C
C Use blocked code initially.
C
IF ( NB.GE.NBMIN .AND. NB.LT.K .AND. NX.LT.K ) THEN
DO 10 I = 1, K - NX, NB
IB = MIN( K-I+1, NB )
C
C Form the triangular factors of the symplectic block
C reflector SH.
C
CALL MB04QF( 'Forward', STOREV, STOREW, M-I+1, IB,
$ V(I,I), LDV, W(I,I), LDW, CS(2*I-1), TAU(I),
$ DWORK(PDRS), NB, DWORK(PDT), NB,
$ DWORK(PDW) )
C
C Apply SH' to [ op(C)(i:m,:); op(D)(i:m,:) ] from the
C left.
C
IF ( LTRC ) THEN
JC = I
ELSE
IC = I
END IF
IF ( LTRD ) THEN
JD = I
ELSE
ID = I
END IF
CALL MB04QC( 'No Structure', TRANC, TRAND, TRANQ,
$ 'Forward', STOREV, STOREW, M-I+1, N, IB,
$ V(I,I), LDV, W(I,I), LDW, DWORK(PDRS), NB,
$ DWORK(PDT), NB, C(IC,JC), LDC, D(ID,JD),
$ LDD, DWORK(PDW) )
10 CONTINUE
ELSE
I = 1
END IF
C
C Use unblocked code to update last or only block.
C
IF ( I.LE.K ) THEN
IF ( LTRC ) THEN
JC = I
ELSE
IC = I
END IF
IF ( LTRD ) THEN
JD = I
ELSE
ID = I
END IF
CALL MB04QU( TRANC, TRAND, TRANQ, STOREV, STOREW, M-I+1, N,
$ K-I+1, V(I,I), LDV, W(I,I), LDW, C(IC,JC), LDC,
$ D(ID,JD), LDD, CS(2*I-1), TAU(I), DWORK,
$ LDWORK, IERR )
END IF
ELSE
IF ( NB.GE.NBMIN .AND. NB.LT.K .AND. NX.LT.K ) THEN
C
C Use blocked code after the last block.
C The first kk columns are handled by the block method.
C
KI = ( ( K-NX-1 ) / NB )*NB
KK = MIN( K, KI+NB )
ELSE
KK = 0
END IF
C
C Use unblocked code for the last or only block.
C
IF ( KK.LT.K ) THEN
IF ( LTRC ) THEN
JC = KK + 1
ELSE
IC = KK + 1
END IF
IF ( LTRD ) THEN
JD = KK + 1
ELSE
ID = KK + 1
END IF
CALL MB04QU( TRANC, TRAND, TRANQ, STOREV, STOREW, M-KK, N,
$ K-KK, V(KK+1,KK+1), LDV, W(KK+1,KK+1), LDW,
$ C(IC,JC), LDC, D(ID,JD), LDD, CS(2*KK+1),
$ TAU(KK+1), DWORK, LDWORK, IERR )
END IF
C
C Blocked code.
C
IF ( KK.GT.0 ) THEN
DO 20 I = KI + 1, 1, -NB
IB = MIN( NB, K-I+1 )
C
C Form the triangular factors of the symplectic block
C reflector SH.
C
CALL MB04QF( 'Forward', STOREV, STOREW, M-I+1, IB,
$ V(I,I), LDV, W(I,I), LDW, CS(2*I-1), TAU(I),
$ DWORK(PDRS), NB, DWORK(PDT), NB,
$ DWORK(PDW) )
C
C Apply SH to [ op(C)(i:m,:); op(D)(i:m,:) ] from
C the left.
C
IF ( LTRC ) THEN
JC = I
ELSE
IC = I
END IF
IF ( LTRD ) THEN
JD = I
ELSE
ID = I
END IF
CALL MB04QC( 'No Structure', TRANC, TRAND, TRANQ,
$ 'Forward', STOREV, STOREW, M-I+1, N, IB,
$ V(I,I), LDV, W(I,I), LDW, DWORK(PDRS), NB,
$ DWORK(PDT), NB, C(IC,JC), LDC, D(ID,JD),
$ LDD, DWORK(PDW) )
20 CONTINUE
END IF
END IF
DWORK(1) = DBLE( WRKOPT )
C
RETURN
C *** Last line of MB04QB ***
END
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