d9/d47/sdsdot_8f_source.html

00001       REAL FUNCTION SDSDOT(N,SB,SX,INCX,SY,INCY)
00002 *     .. Scalar Arguments ..
00003       REAL SB
00004       INTEGER INCX,INCY,N
00005 *     ..
00006 *     .. Array Arguments ..
00007       REAL SX(*),SY(*)
00008 *     ..
00009 *
00010 *  PURPOSE
00011 *  =======
00012 *
00013 *  Compute the inner product of two vectors with extended
00014 *  precision accumulation.
00015 *
00016 *  Returns S.P. result with dot product accumulated in D.P.
00017 *  SDSDOT = SB + sum for I = 0 to N-1 of SX(LX+I*INCX)*SY(LY+I*INCY),
00018 *  where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is
00019 *  defined in a similar way using INCY.
00020 *
00021 *  AUTHOR
00022 *  ======
00023 *  Lawson, C. L., (JPL), Hanson, R. J., (SNLA),
00024 *  Kincaid, D. R., (U. of Texas), Krogh, F. T., (JPL)
00025 *
00026 *  ARGUMENTS
00027 *  =========
00028 *
00029 *  N      (input) INTEGER
00030 *         number of elements in input vector(s)
00031 *
00032 *  SB     (input) REAL
00033 *         single precision scalar to be added to inner product
00034 *
00035 *  SX     (input) REAL array, dimension (N)
00036 *         single precision vector with N elements
00037 *
00038 *  INCX   (input) INTEGER
00039 *         storage spacing between elements of SX
00040 *
00041 *  SY     (input) REAL array, dimension (N)
00042 *         single precision vector with N elements
00043 *
00044 *  INCY   (input) INTEGER
00045 *         storage spacing between elements of SY
00046 *
00047 *  SDSDOT (output) REAL
00048 *         single precision dot product (SB if N .LE. 0)
00049 *
00050 *  Further Details
00051 *  ===============
00052 *
00053 *  REFERENCES
00054 *
00055 *  C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T.
00056 *  Krogh, Basic linear algebra subprograms for Fortran
00057 *  usage, Algorithm No. 539, Transactions on Mathematical
00058 *  Software 5, 3 (September 1979), pp. 308-323.
00059 *
00060 *  REVISION HISTORY  (YYMMDD)
00061 *
00062 *  791001  DATE WRITTEN
00063 *  890531  Changed all specific intrinsics to generic.  (WRB)
00064 *  890831  Modified array declarations.  (WRB)
00065 *  890831  REVISION DATE from Version 3.2
00066 *  891214  Prologue converted to Version 4.0 format.  (BAB)
00067 *  920310  Corrected definition of LX in DESCRIPTION.  (WRB)
00068 *  920501  Reformatted the REFERENCES section.  (WRB)
00069 *  070118  Reformat to LAPACK coding style
00070 *
00071 *  =====================================================================
00072 *
00073 *     .. Local Scalars ..
00074       DOUBLE PRECISION DSDOT
00075       INTEGER I,KX,KY,NS
00076 *     ..
00077 *     .. Intrinsic Functions ..
00078       INTRINSIC DBLE
00079 *     ..
00080       DSDOT = SB
00081       IF (N.LE.0) THEN
00082          SDSDOT = DSDOT
00083          RETURN
00084       END IF
00085       IF (INCX.EQ.INCY .AND. INCX.GT.0) THEN
00086 *
00087 *     Code for equal and positive increments.
00088 *
00089          NS = N*INCX
00090          DO I = 1,NS,INCX
00091             DSDOT = DSDOT + DBLE(SX(I))*DBLE(SY(I))
00092          END DO
00093       ELSE
00094 *
00095 *     Code for unequal or nonpositive increments.
00096 *
00097          KX = 1
00098          KY = 1
00099          IF (INCX.LT.0) KX = 1 + (1-N)*INCX
00100          IF (INCY.LT.0) KY = 1 + (1-N)*INCY
00101          DO I = 1,N
00102             DSDOT = DSDOT + DBLE(SX(KX))*DBLE(SY(KY))
00103             KX = KX + INCX
00104             KY = KY + INCY
00105          END DO
00106       END IF
00107       SDSDOT = DSDOT
00108       RETURN
00109       END