REAL FUNCTION SDSDOT(N,SB,SX,INCX,SY,INCY) * .. Scalar Arguments .. REAL SB INTEGER INCX,INCY,N * .. * .. Array Arguments .. REAL SX(*),SY(*) * .. * * PURPOSE * ======= * * Compute the inner product of two vectors with extended * precision accumulation. * * Returns S.P. result with dot product accumulated in D.P. * SDSDOT = SB + 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. * * AUTHOR * ====== * Lawson, C. L., (JPL), Hanson, R. J., (SNLA), * Kincaid, D. R., (U. of Texas), Krogh, F. T., (JPL) * * ARGUMENTS * ========= * * N (input) INTEGER * number of elements in input vector(s) * * SB (input) REAL * single precision scalar to be added to inner product * * 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 * * SDSDOT (output) REAL * single precision dot product (SB if N .LE. 0) * * 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 * 890531 Changed all specific intrinsics to generic. (WRB) * 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 coding style * * ===================================================================== * * .. Local Scalars .. DOUBLE PRECISION DSDOT INTEGER I,KX,KY,NS * .. * .. Intrinsic Functions .. INTRINSIC DBLE * .. DSDOT = SB IF (N.LE.0) THEN SDSDOT = DSDOT RETURN END IF IF (INCX.EQ.INCY .AND. INCX.GT.0) THEN * * Code for equal and positive 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 SDSDOT = DSDOT RETURN END