*> \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 of DSDOT * END