75 lines
2.5 KiB
Fortran
75 lines
2.5 KiB
Fortran
*DECK DSDOT
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DOUBLE PRECISION FUNCTION DSDOTF (N, SX, INCX, SY, INCY)
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C***BEGIN PROLOGUE DSDOT
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C***PURPOSE Compute the inner product of two vectors with extended
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C precision accumulation and result.
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C***LIBRARY SLATEC (BLAS)
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C***CATEGORY D1A4
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C***TYPE DOUBLE PRECISION (DSDOT-D, DCDOT-C)
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C***KEYWORDS BLAS, COMPLEX VECTORS, DOT PRODUCT, INNER PRODUCT,
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C LINEAR ALGEBRA, 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 SX single precision vector with N elements
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C INCX storage spacing between elements of SX
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C SY single precision vector with N elements
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C INCY storage spacing between elements of SY
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C
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C --Output--
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C DSDOT double precision dot product (zero if N.LE.0)
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C
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C Returns D.P. dot product accumulated in D.P., for S.P. SX and SY
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C DSDOT = sum for I = 0 to N-1 of SX(LX+I*INCX) * SY(LY+I*INCY),
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C where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is
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C defined in a similar way using INCY.
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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 890831 Modified array declarations. (WRB)
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C 890831 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 DSDOT
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REAL SX(*),SY(*)
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C***FIRST EXECUTABLE STATEMENT DSDOT
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DSDOTF = 0.0D0
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IF (N .LE. 0) RETURN
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IF (INCX.EQ.INCY .AND. INCX.GT.0) GO TO 20
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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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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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DO 10 I = 1,N
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DSDOTF = DSDOTF + DBLE(SX(KX))*DBLE(SY(KY))
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KX = KX + INCX
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KY = KY + INCY
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10 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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20 NS = N*INCX
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DO 30 I = 1,NS,INCX
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DSDOTF = DSDOTF + DBLE(SX(I))*DBLE(SY(I))
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30 CONTINUE
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RETURN
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END
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