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