dsdot()

double precision function dsdot	(	integer	n,
		real, dimension(*)	sx,
		integer	incx,
		real, dimension(*)	sy,
		integer	incy
	)

DSDOT

Purpose:

 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.

Parameters

[in]	N	N is INTEGER number of elements in input vector(s)
[in]	SX	SX is REAL array, dimension(N) single precision vector with N elements
[in]	INCX	INCX is INTEGER storage spacing between elements of SX
[in]	SY	SY is REAL array, dimension(N) single precision vector with N elements
[in]	INCY	INCY is INTEGER storage spacing between elements of SY

Returns

DSDOT

          DSDOT is DOUBLE PRECISION
         DSDOT  double precision dot product (zero if N.LE.0)

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Further Details:

References:

  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)

Definition at line 118 of file dsdot.f.

*
*  -- 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
*

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