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150 lines
4.9 KiB
Fortran
150 lines
4.9 KiB
Fortran
*DECK DROTM
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SUBROUTINE DROTM (N, DX, INCX, DY, INCY, DPARAM)
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C***BEGIN PROLOGUE DROTM
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C***PURPOSE Apply a modified Givens transformation.
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C***LIBRARY SLATEC (BLAS)
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C***CATEGORY D1A8
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C***TYPE DOUBLE PRECISION (SROTM-S, DROTM-D)
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C***KEYWORDS BLAS, LINEAR ALGEBRA, MODIFIED GIVENS ROTATION, VECTOR
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C***AUTHOR Lawson, C. L., (JPL)
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C Hanson, R. J., (SNLA)
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C Kincaid, D. R., (U. of Texas)
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C Krogh, F. T., (JPL)
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C***DESCRIPTION
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C
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C B L A S Subprogram
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C Description of Parameters
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C
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C --Input--
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C N number of elements in input vector(s)
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C DX double precision vector with N elements
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C INCX storage spacing between elements of DX
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C DY double precision vector with N elements
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C INCY storage spacing between elements of DY
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C DPARAM 5-element D.P. vector. DPARAM(1) is DFLAG described below.
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C Locations 2-5 of SPARAM contain elements of the
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C transformation matrix H described below.
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C
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C --Output--
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C DX rotated vector (unchanged if N .LE. 0)
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C DY rotated vector (unchanged if N .LE. 0)
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C
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C Apply the modified Givens transformation, H, to the 2 by N matrix
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C (DX**T)
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C (DY**T) , where **T indicates transpose. The elements of DX are
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C in DX(LX+I*INCX), I = 0 to N-1, where LX = 1 if INCX .GE. 0, else
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C LX = 1+(1-N)*INCX, and similarly for DY using LY and INCY.
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C
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C With DPARAM(1)=DFLAG, H has one of the following forms:
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C
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C DFLAG=-1.D0 DFLAG=0.D0 DFLAG=1.D0 DFLAG=-2.D0
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C
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C (DH11 DH12) (1.D0 DH12) (DH11 1.D0) (1.D0 0.D0)
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C H=( ) ( ) ( ) ( )
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C (DH21 DH22), (DH21 1.D0), (-1.D0 DH22), (0.D0 1.D0).
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C
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C See DROTMG for a description of data storage in DPARAM.
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C
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C***REFERENCES C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T.
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C Krogh, Basic linear algebra subprograms for Fortran
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C usage, Algorithm No. 539, Transactions on Mathematical
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C Software 5, 3 (September 1979), pp. 308-323.
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C***ROUTINES CALLED (NONE)
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C***REVISION HISTORY (YYMMDD)
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C 791001 DATE WRITTEN
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C 861211 REVISION DATE from Version 3.2
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C 891214 Prologue converted to Version 4.0 format. (BAB)
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C 920310 Corrected definition of LX in DESCRIPTION. (WRB)
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C 920501 Reformatted the REFERENCES section. (WRB)
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C***END PROLOGUE DROTM
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DOUBLE PRECISION DFLAG, DH12, DH22, DX, TWO, Z, DH11, DH21,
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1 DPARAM, DY, W, ZERO
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DIMENSION DX(*), DY(*), DPARAM(5)
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SAVE ZERO, TWO
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DATA ZERO, TWO /0.0D0, 2.0D0/
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C***FIRST EXECUTABLE STATEMENT DROTM
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DFLAG=DPARAM(1)
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IF (N.LE.0 .OR. (DFLAG+TWO.EQ.ZERO)) GO TO 140
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IF (.NOT.(INCX.EQ.INCY.AND. INCX .GT.0)) GO TO 70
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C
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NSTEPS=N*INCX
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IF (DFLAG) 50,10,30
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10 CONTINUE
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DH12=DPARAM(4)
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DH21=DPARAM(3)
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DO 20 I = 1,NSTEPS,INCX
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W=DX(I)
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Z=DY(I)
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DX(I)=W+Z*DH12
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DY(I)=W*DH21+Z
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20 CONTINUE
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GO TO 140
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30 CONTINUE
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DH11=DPARAM(2)
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DH22=DPARAM(5)
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DO 40 I = 1,NSTEPS,INCX
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W=DX(I)
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Z=DY(I)
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DX(I)=W*DH11+Z
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DY(I)=-W+DH22*Z
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40 CONTINUE
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GO TO 140
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50 CONTINUE
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DH11=DPARAM(2)
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DH12=DPARAM(4)
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DH21=DPARAM(3)
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DH22=DPARAM(5)
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DO 60 I = 1,NSTEPS,INCX
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W=DX(I)
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Z=DY(I)
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DX(I)=W*DH11+Z*DH12
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DY(I)=W*DH21+Z*DH22
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60 CONTINUE
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GO TO 140
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70 CONTINUE
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KX=1
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KY=1
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IF (INCX .LT. 0) KX = 1+(1-N)*INCX
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IF (INCY .LT. 0) KY = 1+(1-N)*INCY
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C
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IF (DFLAG) 120,80,100
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80 CONTINUE
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DH12=DPARAM(4)
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DH21=DPARAM(3)
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DO 90 I = 1,N
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W=DX(KX)
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Z=DY(KY)
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DX(KX)=W+Z*DH12
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DY(KY)=W*DH21+Z
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KX=KX+INCX
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KY=KY+INCY
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90 CONTINUE
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GO TO 140
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100 CONTINUE
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DH11=DPARAM(2)
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DH22=DPARAM(5)
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DO 110 I = 1,N
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W=DX(KX)
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Z=DY(KY)
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DX(KX)=W*DH11+Z
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DY(KY)=-W+DH22*Z
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KX=KX+INCX
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KY=KY+INCY
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110 CONTINUE
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GO TO 140
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120 CONTINUE
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DH11=DPARAM(2)
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DH12=DPARAM(4)
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DH21=DPARAM(3)
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DH22=DPARAM(5)
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DO 130 I = 1,N
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W=DX(KX)
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Z=DY(KY)
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DX(KX)=W*DH11+Z*DH12
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DY(KY)=W*DH21+Z*DH22
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KX=KX+INCX
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KY=KY+INCY
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130 CONTINUE
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140 CONTINUE
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RETURN
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END
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