ddot.f

          DOUBLE PRECISION FUNCTION DDOT(N,DX,INCX,DY,INCY)
    *     .. Scalar Arguments ..
          INTEGER INCX,INCY,N
    *     ..
    *     .. Array Arguments ..
          DOUBLE PRECISION DX(*),DY(*)
    *     ..
    *
    *  Purpose
    *  =======
    *
    *     forms the dot product of two vectors.
    *     uses unrolled loops for increments equal to one.
    *     jack dongarra, linpack, 3/11/78.
    *     modified 12/3/93, array(1) declarations changed to array(*)
    *
    *
    *     .. Local Scalars ..
          DOUBLE PRECISION DTEMP
          INTEGER I,IX,IY,M,MP1
    *     ..
    *     .. Intrinsic Functions ..
          INTRINSIC MOD
    *     ..
          DDOT = 0.0d0
          DTEMP = 0.0d0
          IF (N.LE.0) RETURN
          IF (INCX.EQ.1 .AND. INCY.EQ.1) GO TO 20
    *
    *        code for unequal increments or equal increments
    *          not equal to 1
    *
          IX = 1
          IY = 1
          IF (INCX.LT.0) IX = (-N+1)*INCX + 1
          IF (INCY.LT.0) IY = (-N+1)*INCY + 1
          DO 10 I = 1,N
              DTEMP = DTEMP + DX(IX)*DY(IY)
              IX = IX + INCX
              IY = IY + INCY
       10 CONTINUE
          DDOT = DTEMP
          RETURN
    *
    *        code for both increments equal to 1
    *
    *
    *        clean-up loop
    *
       20 M = MOD(N,5)
          IF (M.EQ.0) GO TO 40
          DO 30 I = 1,M
              DTEMP = DTEMP + DX(I)*DY(I)
       30 CONTINUE
          IF (N.LT.5) GO TO 60
       40 MP1 = M + 1
          DO 50 I = MP1,N,5
              DTEMP = DTEMP + DX(I)*DY(I) + DX(I+1)*DY(I+1) +
         +            DX(I+2)*DY(I+2) + DX(I+3)*DY(I+3) + DX(I+4)*DY(I+4)
       50 CONTINUE
       60 DDOT = DTEMP
          RETURN
          END