LAPACK  3.4.1
LAPACK: Linear Algebra PACKage
ddot.f
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00001 *> \brief \b DDOT
00002 *
00003 *  =========== DOCUMENTATION ===========
00004 *
00005 * Online html documentation available at 
00006 *            http://www.netlib.org/lapack/explore-html/ 
00007 *
00008 *  Definition:
00009 *  ===========
00010 *
00011 *       DOUBLE PRECISION FUNCTION DDOT(N,DX,INCX,DY,INCY)
00012 * 
00013 *       .. Scalar Arguments ..
00014 *       INTEGER INCX,INCY,N
00015 *       ..
00016 *       .. Array Arguments ..
00017 *       DOUBLE PRECISION DX(*),DY(*)
00018 *       ..
00019 *  
00020 *
00021 *> \par Purpose:
00022 *  =============
00023 *>
00024 *> \verbatim
00025 *>
00026 *>    DDOT forms the dot product of two vectors.
00027 *>    uses unrolled loops for increments equal to one.
00028 *> \endverbatim
00029 *
00030 *  Authors:
00031 *  ========
00032 *
00033 *> \author Univ. of Tennessee 
00034 *> \author Univ. of California Berkeley 
00035 *> \author Univ. of Colorado Denver 
00036 *> \author NAG Ltd. 
00037 *
00038 *> \date November 2011
00039 *
00040 *> \ingroup double_blas_level1
00041 *
00042 *> \par Further Details:
00043 *  =====================
00044 *>
00045 *> \verbatim
00046 *>
00047 *>     jack dongarra, linpack, 3/11/78.
00048 *>     modified 12/3/93, array(1) declarations changed to array(*)
00049 *> \endverbatim
00050 *>
00051 *  =====================================================================
00052       DOUBLE PRECISION FUNCTION DDOT(N,DX,INCX,DY,INCY)
00053 *
00054 *  -- Reference BLAS level1 routine (version 3.4.0) --
00055 *  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
00056 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00057 *     November 2011
00058 *
00059 *     .. Scalar Arguments ..
00060       INTEGER INCX,INCY,N
00061 *     ..
00062 *     .. Array Arguments ..
00063       DOUBLE PRECISION DX(*),DY(*)
00064 *     ..
00065 *
00066 *  =====================================================================
00067 *
00068 *     .. Local Scalars ..
00069       DOUBLE PRECISION DTEMP
00070       INTEGER I,IX,IY,M,MP1
00071 *     ..
00072 *     .. Intrinsic Functions ..
00073       INTRINSIC MOD
00074 *     ..
00075       DDOT = 0.0d0
00076       DTEMP = 0.0d0
00077       IF (N.LE.0) RETURN
00078       IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
00079 *
00080 *        code for both increments equal to 1
00081 *
00082 *
00083 *        clean-up loop
00084 *
00085          M = MOD(N,5)
00086          IF (M.NE.0) THEN
00087             DO I = 1,M
00088                DTEMP = DTEMP + DX(I)*DY(I)
00089             END DO
00090             IF (N.LT.5) THEN
00091                DDOT=DTEMP
00092             RETURN
00093             END IF
00094          END IF
00095          MP1 = M + 1
00096          DO I = MP1,N,5
00097           DTEMP = DTEMP + DX(I)*DY(I) + DX(I+1)*DY(I+1) +
00098      $            DX(I+2)*DY(I+2) + DX(I+3)*DY(I+3) + DX(I+4)*DY(I+4)
00099          END DO
00100       ELSE
00101 *
00102 *        code for unequal increments or equal increments
00103 *          not equal to 1
00104 *
00105          IX = 1
00106          IY = 1
00107          IF (INCX.LT.0) IX = (-N+1)*INCX + 1
00108          IF (INCY.LT.0) IY = (-N+1)*INCY + 1
00109          DO I = 1,N
00110             DTEMP = DTEMP + DX(IX)*DY(IY)
00111             IX = IX + INCX
00112             IY = IY + INCY
00113          END DO
00114       END IF
00115       DDOT = DTEMP
00116       RETURN
00117       END
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