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83 lines
2.3 KiB
Fortran
83 lines
2.3 KiB
Fortran
*DECK DCOPYM
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SUBROUTINE DCOPYM (N, DX, INCX, DY, INCY)
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C***BEGIN PROLOGUE DCOPYM
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C***PURPOSE Copy the negative of a vector to a vector.
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C***LIBRARY SLATEC (BLAS)
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C***CATEGORY D1A5
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C***TYPE DOUBLE PRECISION (SCOPYM-S, DCOPYM-D)
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C***KEYWORDS BLAS, COPY, VECTOR
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C***AUTHOR Kahaner, D. K., (NBS)
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C***DESCRIPTION
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C
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C Description of Parameters
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C The * Flags Output Variables
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C
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C N Number of elements in 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 negative copy of DX
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C INCY Storage spacing between elements of DY
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C
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C *** Note that DY = -DX ***
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C
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C Copy negative of d.p. DX to d.p. DY. For I=0 to N-1,
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C copy -DX(LX+I*INCX) to DY(LY+I*INCY), where LX=1 if
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C INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is defined
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C in a similar way using INCY.
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C
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C***REFERENCES (NONE)
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C***ROUTINES CALLED (NONE)
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C***REVISION HISTORY (YYMMDD)
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C 801001 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***END PROLOGUE DCOPYM
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DOUBLE PRECISION DX(*), DY(*)
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C***FIRST EXECUTABLE STATEMENT DCOPYM
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IF (N .LE. 0) RETURN
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IF (INCX .EQ. INCY) IF (INCX-1) 5,20,60
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C
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C Code for unequal or nonpositive increments.
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C
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5 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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DO 10 I = 1,N
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DY(IY) = -DX(IX)
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IX = IX + INCX
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IY = IY + INCY
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10 CONTINUE
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RETURN
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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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C Clean-up loop so remaining vector length is a multiple of 7.
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C
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20 M = MOD(N,7)
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IF (M .EQ. 0) GO TO 40
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DO 30 I = 1,M
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DY(I) = -DX(I)
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30 CONTINUE
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IF (N .LT. 7) RETURN
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40 MP1 = M + 1
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DO 50 I = MP1,N,7
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DY(I) = -DX(I)
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DY(I+1) = -DX(I+1)
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DY(I+2) = -DX(I+2)
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DY(I+3) = -DX(I+3)
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DY(I+4) = -DX(I+4)
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DY(I+5) = -DX(I+5)
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DY(I+6) = -DX(I+6)
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50 CONTINUE
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RETURN
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C
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C Code for equal, positive, non-unit increments.
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C
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60 NS = N*INCX
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DO 70 I = 1,NS,INCX
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DY(I) = -DX(I)
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70 CONTINUE
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RETURN
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END
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