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SUBROUTINE TG01CD( COMPQ, L, N, M, A, LDA, E, LDE, B, LDB, Q, LDQ,
$ 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 reduce the descriptor system pair (A-lambda E,B) to the
C QR-coordinate form by computing an orthogonal transformation
C matrix Q such that the transformed descriptor system pair
C (Q'*A-lambda Q'*E, Q'*B) has the descriptor matrix Q'*E
C in an upper trapezoidal form.
C The left orthogonal transformations performed to reduce E
C can be optionally accumulated.
C
C ARGUMENTS
C
C Mode Parameters
C
C COMPQ CHARACTER*1
C = 'N': do not compute Q;
C = 'I': Q is initialized to the unit matrix, and the
C orthogonal matrix Q is returned;
C = 'U': Q must contain an orthogonal matrix Q1 on entry,
C and the product Q1*Q is returned.
C
C Input/Output Parameters
C
C L (input) INTEGER
C The number of rows of matrices A, B, and E. L >= 0.
C
C N (input) INTEGER
C The number of columns of matrices A and E. N >= 0.
C
C M (input) INTEGER
C The number of columns of matrix B. M >= 0.
C
C A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
C On entry, the leading L-by-N part of this array must
C contain the state dynamics matrix A.
C On exit, the leading L-by-N part of this array contains
C the transformed matrix Q'*A.
C
C LDA INTEGER
C The leading dimension of array A. LDA >= MAX(1,L).
C
C E (input/output) DOUBLE PRECISION array, dimension (LDE,N)
C On entry, the leading L-by-N part of this array must
C contain the descriptor matrix E.
C On exit, the leading L-by-N part of this array contains
C the transformed matrix Q'*E in upper trapezoidal form,
C i.e.
C
C ( E11 )
C Q'*E = ( ) , if L >= N ,
C ( 0 )
C or
C
C Q'*E = ( E11 E12 ), if L < N ,
C
C where E11 is an MIN(L,N)-by-MIN(L,N) upper triangular
C matrix.
C
C LDE INTEGER
C The leading dimension of array E. LDE >= MAX(1,L).
C
C B (input/output) DOUBLE PRECISION array, dimension (LDB,M)
C On entry, the leading L-by-M part of this array must
C contain the input/state matrix B.
C On exit, the leading L-by-M part of this array contains
C the transformed matrix Q'*B.
C
C LDB INTEGER
C The leading dimension of array B.
C LDB >= MAX(1,L) if M > 0 or LDB >= 1 if M = 0.
C
C Q (input/output) DOUBLE PRECISION array, dimension (LDQ,L)
C If COMPQ = 'N': Q is not referenced.
C If COMPQ = 'I': on entry, Q need not be set;
C on exit, the leading L-by-L part of this
C array contains the orthogonal matrix Q,
C where Q' is the product of Householder
C transformations which are applied to A,
C E, and B on the left.
C If COMPQ = 'U': on entry, the leading L-by-L part of this
C array must contain an orthogonal matrix
C Q1;
C on exit, the leading L-by-L part of this
C array contains the orthogonal matrix
C Q1*Q.
C
C LDQ INTEGER
C The leading dimension of array Q.
C LDQ >= 1, if COMPQ = 'N';
C LDQ >= MAX(1,L), if COMPQ = 'U' or 'I'.
C
C Workspace
C
C DWORK DOUBLE PRECISION array, dimension (LDWORK)
C On exit, if INFO = 0, DWORK(1) returns the optimal value
C of LDWORK.
C
C LDWORK INTEGER
C The length of the array DWORK.
C LDWORK >= MAX(1, MIN(L,N) + MAX(L,N,M)).
C For optimum performance
C LWORK >= MAX(1, MIN(L,N) + MAX(L,N,M)*NB),
C where NB is the optimal blocksize.
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 METHOD
C
C The routine computes the QR factorization of E to reduce it
C to the upper trapezoidal form.
C
C The transformations are also applied to the rest of system
C matrices
C
C A <- Q' * A , B <- Q' * B.
C
C NUMERICAL ASPECTS
C
C The algorithm is numerically backward stable and requires
C 0( L*L*N ) floating point operations.
C
C CONTRIBUTOR
C
C C. Oara, University "Politehnica" Bucharest.
C A. Varga, German Aerospace Center, DLR Oberpfaffenhofen.
C March 1999. Based on the RASP routine RPDSQR.
C
C REVISIONS
C
C V. Sima, Research Institute for Informatics, Bucharest, July 1999,
C May 2003.
C
C KEYWORDS
C
C Descriptor system, matrix algebra, matrix operations,
C orthogonal transformation.
C
C ******************************************************************
C
C .. Parameters ..
DOUBLE PRECISION ONE, ZERO
PARAMETER ( ONE = 1.0D0, ZERO = 0.0D0 )
C .. Scalar Arguments ..
CHARACTER COMPQ
INTEGER INFO, L, LDA, LDB, LDE, LDQ, LDWORK, M, N
C .. Array Arguments ..
DOUBLE PRECISION A( LDA, * ), B( LDB, * ), DWORK( * ),
$ E( LDE, * ), Q( LDQ, * )
C .. Local Scalars ..
LOGICAL ILQ
INTEGER ICOMPQ, LN, WRKOPT
C .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
C .. External Subroutines ..
EXTERNAL DGEQRF, DLASET, DORMQR, XERBLA
C .. Intrinsic Functions ..
INTRINSIC INT, MAX, MIN
C
C .. Executable Statements ..
C
C Decode COMPQ.
C
IF( LSAME( COMPQ, 'N' ) ) THEN
ILQ = .FALSE.
ICOMPQ = 1
ELSE IF( LSAME( COMPQ, 'U' ) ) THEN
ILQ = .TRUE.
ICOMPQ = 2
ELSE IF( LSAME( COMPQ, 'I' ) ) THEN
ILQ = .TRUE.
ICOMPQ = 3
ELSE
ICOMPQ = 0
END IF
C
C Test the input parameters.
C
INFO = 0
WRKOPT = MAX( 1, MIN( L, N ) + MAX( L, N, M ) )
IF( ICOMPQ.EQ.0 ) THEN
INFO = -1
ELSE IF( L.LT.0 ) THEN
INFO = -2
ELSE IF( N.LT.0 ) THEN
INFO = -3
ELSE IF( M.LT.0 ) THEN
INFO = -4
ELSE IF( LDA.LT.MAX( 1, L ) ) THEN
INFO = -6
ELSE IF( LDE.LT.MAX( 1, L ) ) THEN
INFO = -8
ELSE IF( LDB.LT.1 .OR. ( M.GT.0 .AND. LDB.LT.L ) ) THEN
INFO = -10
ELSE IF( ( ILQ .AND. LDQ.LT.L ) .OR. LDQ.LT.1 ) THEN
INFO = -12
ELSE IF( LDWORK.LT.WRKOPT ) THEN
INFO = -14
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'TG01CD', -INFO )
RETURN
END IF
C
C Initialize Q if necessary.
C
IF( ICOMPQ.EQ.3 )
$ CALL DLASET( 'Full', L, L, ZERO, ONE, Q, LDQ )
C
C Quick return if possible.
C
IF( L.EQ.0 .OR. N.EQ.0 ) THEN
DWORK(1) = ONE
RETURN
END IF
C
LN = MIN( L, N )
C
C Compute the QR decomposition of E.
C
C Workspace: need MIN(L,N) + N;
C prefer MIN(L,N) + N*NB.
C
CALL DGEQRF( L, N, E, LDE, DWORK, DWORK( LN+1 ), LDWORK-LN, INFO )
WRKOPT = MAX( WRKOPT, INT( DWORK( LN+1 ) ) + LN )
C
C Apply transformation on the rest of matrices.
C
C A <-- Q' * A.
C Workspace: need MIN(L,N) + N;
C prefer MIN(L,N) + N*NB.
C
CALL DORMQR( 'Left', 'Transpose', L, N, LN, E, LDE, DWORK,
$ A, LDA, DWORK( LN+1 ), LDWORK-LN, INFO )
WRKOPT = MAX( WRKOPT, INT( DWORK( LN+1 ) ) + LN )
C
C B <-- Q' * B.
C Workspace: need MIN(L,N) + M;
C prefer MIN(L,N) + M*NB.
C
IF ( M.GT.0 ) THEN
CALL DORMQR( 'Left', 'Transpose', L, M, LN, E, LDE, DWORK,
$ B, LDB, DWORK( LN+1 ), LDWORK-LN, INFO )
WRKOPT = MAX( WRKOPT, INT( DWORK( LN+1 ) ) + LN )
END IF
C
C Q <-- Q1 * Q.
C Workspace: need MIN(L,N) + L;
C prefer MIN(L,N) + L*NB.
C
IF( ILQ ) THEN
CALL DORMQR( 'Right', 'No Transpose', L, L, LN, E, LDE, DWORK,
$ Q, LDQ, DWORK( LN+1 ), LDWORK-LN, INFO )
WRKOPT = MAX( WRKOPT, INT( DWORK( LN+1 ) ) + LN )
END IF
C
C Set lower triangle of E to zero.
C
IF( L.GE.2 )
$ CALL DLASET( 'Lower', L-1, LN, ZERO, ZERO, E( 2, 1 ), LDE )
C
DWORK(1) = WRKOPT
C
RETURN
C *** Last line of TG01CD ***
END
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