173 lines
4.1 KiB
Fortran
173 lines
4.1 KiB
Fortran
*> \brief \b DSDOT
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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* Definition:
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* ===========
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*
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* DOUBLE PRECISION FUNCTION DSDOT(N,SX,INCX,SY,INCY)
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*
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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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* REAL SX(*),SY(*)
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* ..
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*
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* AUTHORS
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* =======
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* Lawson, C. L., (JPL), Hanson, R. J., (SNLA),
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* Kincaid, D. R., (U. of Texas), Krogh, F. T., (JPL)
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> Compute the inner product of two vectors with extended
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*> precision accumulation and result.
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*>
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*> Returns D.P. dot product accumulated in D.P., for S.P. SX and SY
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*> DSDOT = sum for I = 0 to N-1 of SX(LX+I*INCX) * SY(LY+I*INCY),
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*> where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is
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*> defined in a similar way using INCY.
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> number of elements in input vector(s)
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*> \endverbatim
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*>
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*> \param[in] SX
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*> \verbatim
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*> SX is REAL array, dimension(N)
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*> single precision vector with N elements
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*> \endverbatim
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*>
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*> \param[in] INCX
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*> \verbatim
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*> INCX is INTEGER
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*> storage spacing between elements of SX
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*> \endverbatim
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*>
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*> \param[in] SY
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*> \verbatim
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*> SY is REAL array, dimension(N)
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*> single precision vector with N elements
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*> \endverbatim
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*>
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*> \param[in] INCY
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*> \verbatim
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*> INCY is INTEGER
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*> storage spacing between elements of SY
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*> \endverbatim
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*>
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*> \result DSDOT
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*> \verbatim
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*> DSDOT is DOUBLE PRECISION
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*> DSDOT double precision dot product (zero if N.LE.0)
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \date November 2011
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*
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*> \ingroup double_blas_level1
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*
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*> \par Further Details:
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* =====================
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*>
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*> \verbatim
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*> \endverbatim
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*
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*> \par References:
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* ================
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*>
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*> \verbatim
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*>
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*>
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*> C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T.
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*> Krogh, Basic linear algebra subprograms for Fortran
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*> usage, Algorithm No. 539, Transactions on Mathematical
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*> Software 5, 3 (September 1979), pp. 308-323.
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*>
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*> REVISION HISTORY (YYMMDD)
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*>
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*> 791001 DATE WRITTEN
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*> 890831 Modified array declarations. (WRB)
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*> 890831 REVISION DATE from Version 3.2
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*> 891214 Prologue converted to Version 4.0 format. (BAB)
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*> 920310 Corrected definition of LX in DESCRIPTION. (WRB)
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*> 920501 Reformatted the REFERENCES section. (WRB)
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*> 070118 Reformat to LAPACK style (JL)
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*> \endverbatim
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*>
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* =====================================================================
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DOUBLE PRECISION FUNCTION DSDOT(N,SX,INCX,SY,INCY)
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*
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* -- Reference BLAS level1 routine (version 3.4.0) --
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* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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* November 2011
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*
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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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REAL SX(*),SY(*)
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* ..
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*
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* Authors:
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* ========
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* Lawson, C. L., (JPL), Hanson, R. J., (SNLA),
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* Kincaid, D. R., (U. of Texas), Krogh, F. T., (JPL)
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*
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* =====================================================================
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*
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* .. Local Scalars ..
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INTEGER I,KX,KY,NS
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC DBLE
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* ..
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DSDOT = 0.0D0
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IF (N.LE.0) RETURN
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IF (INCX.EQ.INCY .AND. INCX.GT.0) THEN
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*
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* Code for equal, positive, non-unit increments.
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*
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NS = N*INCX
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DO I = 1,NS,INCX
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DSDOT = DSDOT + DBLE(SX(I))*DBLE(SY(I))
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END DO
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ELSE
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*
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* Code for unequal or nonpositive increments.
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*
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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 I = 1,N
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DSDOT = DSDOT + DBLE(SX(KX))*DBLE(SY(KY))
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KX = KX + INCX
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KY = KY + INCY
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END DO
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END IF
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RETURN
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END
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