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DOUBLE PRECISION FUNCTION DDOT(N,DX,INCX,DY,INCY)
* .. Scalar Arguments ..
INTEGER INCX,INCY,N
* ..
* .. Array Arguments ..
DOUBLE PRECISION DX(*),DY(*)
* ..
*
* Purpose
* =======
*
* DDOT forms the dot product of two vectors.
* uses unrolled loops for increments equal to one.
*
* Further Details
* ===============
*
* 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) THEN
*
* code for both increments equal to 1
*
*
* clean-up loop
*
M = MOD(N,5)
IF (M.NE.0) THEN
DO I = 1,M
DTEMP = DTEMP + DX(I)*DY(I)
END DO
IF (N.LT.5) THEN
DDOT=DTEMP
RETURN
END IF
END IF
MP1 = M + 1
DO 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)
END DO
ELSE
*
* 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 I = 1,N
DTEMP = DTEMP + DX(IX)*DY(IY)
IX = IX + INCX
IY = IY + INCY
END DO
END IF
DDOT = DTEMP
RETURN
END
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