97 lines
2.7 KiB
Fortran
97 lines
2.7 KiB
Fortran
SUBROUTINE MB04TU( N, X, INCX, Y, INCY, C, S )
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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 the Givens transformation, defined by C (cos) and S
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C (sin), and interchange the vectors involved, i.e.
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C
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C |X(i)| | 0 1 | | C S | |X(i)|
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C | | := | | x | | x | |, i = 1,...N.
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C |Y(i)| | 1 0 | |-S C | |Y(i)|
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C
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C REMARK. This routine is a modification of DROT from BLAS.
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C This routine is called only by the SLICOT routines MB04TX
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C and MB04VX.
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C
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C NUMERICAL ASPECTS
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C
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C The algorithm is backward stable.
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C
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C CONTRIBUTOR
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C
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C Release 3.0: V. Sima, Katholieke Univ. Leuven, Belgium, Apr. 1997.
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C Supersedes Release 2.0 routine MB04FU by Th.G.J. Beelen,
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C Philips Glass Eindhoven, Holland.
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C
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C REVISIONS
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C
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C January 26, 1998.
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C
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C KEYWORDS
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C
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C Othogonal transformation.
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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, INCY, N
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DOUBLE PRECISION C, S
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C .. Array Arguments ..
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DOUBLE PRECISION X(*), Y(*)
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C .. Local Scalars ..
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DOUBLE PRECISION DTEMP
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INTEGER I, IX, IY
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C .. Executable Statements ..
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C
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IF ( N.LE.0 ) RETURN
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IF ( ( INCX.NE.1 ) .OR. ( INCY.NE.1 ) ) THEN
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C
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C Code for unequal increments or equal increments not equal to 1.
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C
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IX = 1
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IY = 1
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IF ( INCX.LT.0 ) IX = (-N+1)*INCX + 1
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IF ( INCY.LT.0 ) IY = (-N+1)*INCY + 1
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C
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DO 20 I = 1, N
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DTEMP = C*Y(IY) - S*X(IX)
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Y(IY) = C*X(IX) + S*Y(IY)
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X(IX) = DTEMP
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IX = IX + INCX
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IY = IY + INCY
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20 CONTINUE
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C
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ELSE
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C
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C Code for both increments equal to 1.
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C
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DO 40 I = 1, N
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DTEMP = C*Y(I) - S*X(I)
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Y(I) = C*X(I) + S*Y(I)
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X(I) = DTEMP
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40 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 *** Last line of MB04TU ***
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END
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