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148 lines
3.7 KiB
FortranFixed
148 lines
3.7 KiB
FortranFixed
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SUBROUTINE DROTM(N,DX,INCX,DY,INCY,DPARAM)
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* .. Scalar Arguments ..
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INTEGER INCX,INCY,N
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION DPARAM(5),DX(*),DY(*)
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* ..
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*
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* Purpose
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* =======
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*
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* APPLY THE MODIFIED GIVENS TRANSFORMATION, H, TO THE 2 BY N MATRIX
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*
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* (DX**T) , WHERE **T INDICATES TRANSPOSE. THE ELEMENTS OF DX ARE IN
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* (DY**T)
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*
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* DX(LX+I*INCX), I = 0 TO N-1, WHERE LX = 1 IF INCX .GE. 0, ELSE
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* LX = (-INCX)*N, AND SIMILARLY FOR SY USING LY AND INCY.
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* WITH DPARAM(1)=DFLAG, H HAS ONE OF THE FOLLOWING FORMS..
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*
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* DFLAG=-1.D0 DFLAG=0.D0 DFLAG=1.D0 DFLAG=-2.D0
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*
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* (DH11 DH12) (1.D0 DH12) (DH11 1.D0) (1.D0 0.D0)
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* H=( ) ( ) ( ) ( )
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* (DH21 DH22), (DH21 1.D0), (-1.D0 DH22), (0.D0 1.D0).
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* SEE DROTMG FOR A DESCRIPTION OF DATA STORAGE IN DPARAM.
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*
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* Arguments
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* =========
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*
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* N (input) INTEGER
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* number of elements in input vector(s)
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*
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* DX (input/output) DOUBLE PRECISION array, dimension N
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* double precision vector with N elements
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*
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* INCX (input) INTEGER
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* storage spacing between elements of DX
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*
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* DY (input/output) DOUBLE PRECISION array, dimension N
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* double precision vector with N elements
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*
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* INCY (input) INTEGER
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* storage spacing between elements of DY
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*
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* DPARAM (input/output) DOUBLE PRECISION array, dimension 5
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* DPARAM(1)=DFLAG
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* DPARAM(2)=DH11
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* DPARAM(3)=DH21
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* DPARAM(4)=DH12
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* DPARAM(5)=DH22
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*
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* =====================================================================
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*
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* .. Local Scalars ..
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DOUBLE PRECISION DFLAG,DH11,DH12,DH21,DH22,TWO,W,Z,ZERO
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INTEGER I,KX,KY,NSTEPS
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* ..
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* .. Data statements ..
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DATA ZERO,TWO/0.D0,2.D0/
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* ..
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*
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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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*
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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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*
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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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