159 lines
4.8 KiB
Fortran
159 lines
4.8 KiB
Fortran
SUBROUTINE MA02GD( N, A, LDA, K1, K2, IPIV, INCX )
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C
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C SLICOT RELEASE 5.0.
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C
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C Copyright (c) 2002-2009 NICONET e.V.
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C
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C This program is free software: you can redistribute it and/or
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C modify it under the terms of the GNU General Public License as
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C published by the Free Software Foundation, either version 2 of
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C the License, or (at your option) any later version.
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C
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C This program is distributed in the hope that it will be useful,
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C but WITHOUT ANY WARRANTY; without even the implied warranty of
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C MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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C GNU General Public License for more details.
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C
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C You should have received a copy of the GNU General Public License
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C along with this program. If not, see
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C <http://www.gnu.org/licenses/>.
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C
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C PURPOSE
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C
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C To perform a series of column interchanges on the matrix A.
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C One column interchange is initiated for each of columns K1 through
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C K2 of A. This is useful for solving linear systems X*A = B, when
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C the matrix A has already been factored by LAPACK Library routine
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C DGETRF.
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C
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C ARGUMENTS
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C
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C Input/Output Parameters
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C
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C N (input) INTEGER
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C The number of rows of the matrix A. N >= 0.
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C
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C A (input/output) DOUBLE PRECISION array, dimension (LDA,*)
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C On entry, the leading N-by-M part of this array must
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C contain the matrix A to which the column interchanges will
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C be applied, where M is the largest element of IPIV(K), for
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C K = K1, ..., K2.
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C On exit, the leading N-by-M part of this array contains
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C the permuted matrix.
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C
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C LDA INTEGER
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C The leading dimension of the array A. LDA >= MAX(1,N).
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C
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C K1 (input) INTEGER
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C The first element of IPIV for which a column interchange
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C will be done.
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C
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C K2 (input) INTEGER
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C The last element of IPIV for which a column interchange
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C will be done.
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C
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C IPIV (input) INTEGER array, dimension (K1+(K2-K1)*abs(INCX))
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C The vector of interchanging (pivot) indices. Only the
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C elements in positions K1 through K2 of IPIV are accessed.
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C IPIV(K) = L implies columns K and L are to be
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C interchanged.
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C
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C INCX (input) INTEGER
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C The increment between successive values of IPIV.
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C If INCX is negative, the interchanges are applied in
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C reverse order.
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C
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C METHOD
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C
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C The columns IPIV(K) and K are swapped for K = K1, ..., K2, for
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C INCX = 1 (and similarly, for INCX <> 1).
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C
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C FURTHER COMMENTS
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C
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C This routine is the column-oriented counterpart of the LAPACK
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C Library routine DLASWP. The LAPACK Library routine DLAPMT cannot
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C be used in this context. To solve the system X*A = B, where A and
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C B are N-by-N and M-by-N, respectively, the following statements
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C can be used:
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C
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C CALL DGETRF( N, N, A, LDA, IPIV, INFO )
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C CALL DTRSM( 'R', 'U', 'N', 'N', M, N, ONE, A, LDA, B, LDB )
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C CALL DTRSM( 'R', 'L', 'N', 'U', M, N, ONE, A, LDA, B, LDB )
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C CALL MA02GD( M, B, LDB, 1, N, IPIV, -1 )
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C
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C CONTRIBUTOR
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C
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C V. Sima, Research Institute for Informatics, Bucharest, Mar. 2000.
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C
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C REVISIONS
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C
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C V. Sima, Research Institute for Informatics, Bucharest, Apr. 2008.
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C
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C KEYWORDS
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C
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C Elementary matrix operations, linear algebra.
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C
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C ******************************************************************
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C
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C .. Scalar Arguments ..
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INTEGER INCX, K1, K2, LDA, N
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C ..
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C .. Array Arguments ..
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INTEGER IPIV( * )
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DOUBLE PRECISION A( LDA, * )
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C ..
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C .. Local Scalars ..
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INTEGER J, JP, JX
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C ..
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C .. External Subroutines ..
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EXTERNAL DSWAP
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C ..
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C .. Executable Statements ..
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C
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C Quick return if possible.
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C
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IF( INCX.EQ.0 .OR. N.EQ.0 )
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$ RETURN
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C
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C Interchange column J with column IPIV(J) for each of columns K1
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C through K2.
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C
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IF( INCX.GT.0 ) THEN
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JX = K1
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ELSE
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JX = 1 + ( 1-K2 )*INCX
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END IF
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C
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IF( INCX.EQ.1 ) THEN
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C
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DO 10 J = K1, K2
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JP = IPIV( J )
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IF( JP.NE.J )
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$ CALL DSWAP( N, A( 1, J ), 1, A( 1, JP ), 1 )
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10 CONTINUE
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C
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ELSE IF( INCX.GT.1 ) THEN
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C
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DO 20 J = K1, K2
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JP = IPIV( JX )
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IF( JP.NE.J )
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$ CALL DSWAP( N, A( 1, J ), 1, A( 1, JP ), 1 )
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JX = JX + INCX
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20 CONTINUE
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C
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ELSE IF( INCX.LT.0 ) THEN
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C
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DO 30 J = K2, K1, -1
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JP = IPIV( JX )
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IF( JP.NE.J )
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$ CALL DSWAP( N, A( 1, J ), 1, A( 1, JP ), 1 )
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JX = JX + INCX
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30 CONTINUE
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C
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END IF
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C
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RETURN
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C
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C *** Last line of MA02GD ***
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END
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