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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)
*
* 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.
*
* Arguments
* =========
*
* N (input) INTEGER
* number of elements in input vector(s)
*
* SX (input) REAL array, dimension(N)
* single precision vector with N elements
*
* INCX (input) INTEGER
* storage spacing between elements of SX
*
* SY (input) REAL array, dimension(N)
* single precision vector with N elements
*
* INCY (input) INTEGER
* storage spacing between elements of SY
*
* DSDOT (output) DOUBLE PRECISION
* DSDOT double precision dot product (zero if N.LE.0)
*
* 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)
*
* =====================================================================
*
* .. 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) GO TO 20
*
* 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 10 I = 1,N
DSDOT = DSDOT + DBLE(SX(KX))*DBLE(SY(KY))
KX = KX + INCX
KY = KY + INCY
10 CONTINUE
RETURN
*
* Code for equal, positive, non-unit increments.
*
20 NS = N*INCX
DO 30 I = 1,NS,INCX
DSDOT = DSDOT + DBLE(SX(I))*DBLE(SY(I))
30 CONTINUE
RETURN
END
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