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SUBROUTINE MB05OY( JOB, N, LOW, IGH, A, LDA, SCALE, 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 restore a matrix after it has been transformed by applying
C balancing transformations (permutations and scalings), as
C determined by LAPACK Library routine DGEBAL.
C
C ARGUMENTS
C
C Mode Parameters
C
C JOB CHARACTER*1
C Specifies the type of backward transformation required,
C as follows:
C = 'N', do nothing, return immediately;
C = 'P', do backward transformation for permutation only;
C = 'S', do backward transformation for scaling only;
C = 'B', do backward transformations for both permutation
C and scaling.
C JOB must be the same as the argument JOB supplied
C to DGEBAL.
C
C Input/Output Parameters
C
C N (input) INTEGER
C The order of the matrix A. N >= 0.
C
C LOW (input) INTEGER
C IGH (input) INTEGER
C The integers LOW and IGH determined by DGEBAL.
C 1 <= LOW <= IGH <= N, if N > 0; LOW=1 and IGH=0, if N=0.
C
C A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
C On entry, the leading N-by-N part of this array must
C contain the matrix to be back-transformed.
C On exit, the leading N-by-N part of this array contains
C the transformed matrix.
C
C LDA INTEGER
C The leading dimension of the array A. LDA >= max(1,N).
C
C SCALE (input) DOUBLE PRECISION array, dimension (N)
C Details of the permutation and scaling factors, as
C returned by DGEBAL.
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 Let P be a permutation matrix, and D a diagonal matrix of scaling
C factors, both of order N. The routine computes
C -1
C A <-- P D A D P'.
C
C where the permutation and scaling factors are encoded in the
C array SCALE.
C
C REFERENCES
C
C None.
C
C NUMERICAL ASPECTS
C 2
C The algorithm requires O(N ) operations.
C
C CONTRIBUTORS
C
C Release 3.0: V. Sima, Katholieke Univ. Leuven, Belgium, Apr. 1997.
C Supersedes Release 2.0 routine MB05CY.
C
C REVISIONS
C
C -
C
C KEYWORDS
C
C Elementary matrix operations, matrix algebra, matrix operations.
C
C ******************************************************************
C
DOUBLE PRECISION ONE
PARAMETER ( ONE = 1.0D0 )
C .. Scalar Arguments ..
CHARACTER JOB
INTEGER IGH, INFO, LDA, LOW, N
C .. Array Arguments ..
DOUBLE PRECISION A(LDA,*), SCALE(*)
C .. Local Scalars ..
INTEGER I, II, J, K
C .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
C .. External Subroutines ..
EXTERNAL DSCAL, DSWAP, XERBLA
C .. Intrinsic Functions ..
INTRINSIC MAX, MIN
C .. Executable Statements ..
C
C Test the input scalar arguments.
C
INFO = 0
IF( .NOT.LSAME( JOB, 'N' ) .AND. .NOT.LSAME( JOB, 'P' ) .AND.
$ .NOT.LSAME( JOB, 'S' ) .AND. .NOT.LSAME( JOB, 'B' ) ) THEN
INFO = -1
ELSE IF( N.LT.0 )THEN
INFO = -2
ELSE IF( LOW.LT.1 .OR. LOW.GT.MAX( 1, N ) ) THEN
INFO = -3
ELSE IF( IGH.LT.MIN( LOW, N ) .OR. IGH.GT.N ) THEN
INFO = -4
ELSE IF( LDA.LT.MAX( 1, N ) )THEN
INFO = -6
END IF
C
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'MB05OY', -INFO )
RETURN
END IF
C
C Quick return if possible.
C
IF( N.EQ.0 .OR. LSAME( JOB, 'N' ) )
$ RETURN
C
IF ( .NOT.LSAME( JOB, 'P' ) .AND. IGH.NE.LOW ) THEN
C
DO 20 I = LOW, IGH
CALL DSCAL( N, SCALE(I), A(I,1), LDA )
20 CONTINUE
C
DO 40 J = LOW, IGH
CALL DSCAL( N, ONE/SCALE(J), A(1,J), 1 )
40 CONTINUE
C
END IF
C
IF( .NOT.LSAME( JOB, 'S' ) ) THEN
C
DO 60 II = 1, N
I = II
IF ( I.LT.LOW .OR. I.GT.IGH ) THEN
IF ( I.LT.LOW ) I = LOW - II
K = SCALE(I)
IF ( K.NE.I ) THEN
CALL DSWAP( N, A(I,1), LDA, A(K,1), LDA )
CALL DSWAP( N, A(1,I), 1, A(1,K), 1 )
END IF
END IF
60 CONTINUE
C
END IF
C
RETURN
C *** Last line of MB05OY ***
END
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