114 lines
3.5 KiB
Fortran
114 lines
3.5 KiB
Fortran
SUBROUTINE MA02CD( N, KL, KU, A, LDA )
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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 compute the pertranspose of a central band of a square matrix.
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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 order of the square matrix A. N >= 0.
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C
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C KL (input) INTEGER
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C The number of subdiagonals of A to be pertransposed.
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C 0 <= KL <= N-1.
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C
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C KU (input) INTEGER
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C The number of superdiagonals of A to be pertransposed.
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C 0 <= KU <= N-1.
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C
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C A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
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C On entry, the leading N-by-N part of this array must
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C contain a square matrix whose central band formed from
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C the KL subdiagonals, the main diagonal and the KU
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C superdiagonals will be pertransposed.
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C On exit, the leading N-by-N part of this array contains
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C the matrix A with its central band (the KL subdiagonals,
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C the main diagonal and the KU superdiagonals) pertransposed
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C (that is the elements of each antidiagonal appear in
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C reversed order). This is equivalent to forming P*B'*P,
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C where B is the matrix formed from the central band of A
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C and P is a permutation matrix with ones down the secondary
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C diagonal.
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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 CONTRIBUTOR
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C
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C A. Varga, German Aerospace Center,
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C DLR Oberpfaffenhofen, March 1998.
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C Based on the RASP routine DMPTR.
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C
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C REVISIONS
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C
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C A. Varga, December 2001.
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C V. Sima, March 2004.
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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 KL, KU, LDA, N
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C .. Array Arguments ..
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DOUBLE PRECISION A(LDA,*)
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C .. Local Scalars ..
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INTEGER I, I1, LDA1
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C .. External Subroutines ..
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EXTERNAL DSWAP
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C .. Intrinsic Functions ..
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INTRINSIC MIN
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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( N.LE.1 )
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$ RETURN
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C
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LDA1 = LDA + 1
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C
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C Pertranspose the KL subdiagonals.
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C
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DO 10 I = 1, MIN( KL, N-2 )
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I1 = (N-I) / 2
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IF( I1.GT.0 )
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$ CALL DSWAP( I1, A(I+1,1), LDA1, A(N-I1+1,N-I1+1-I), -LDA1 )
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10 CONTINUE
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C
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C Pertranspose the KU superdiagonals.
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C
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DO 20 I = 1, MIN( KU, N-2 )
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I1 = (N-I) / 2
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IF( I1.GT.0 )
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$ CALL DSWAP( I1, A(1,I+1), LDA1, A(N-I1+1-I,N-I1+1), -LDA1 )
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20 CONTINUE
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C
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C Pertranspose the diagonal.
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C
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I1 = N / 2
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IF( I1.GT.0 )
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$ CALL DSWAP( I1, A(1,1), LDA1, A(N-I1+1,N-I1+1), -LDA1 )
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C
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RETURN
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C *** Last line of MA02CD ***
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END
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