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