x = SUM_SCATTER( flux, x, nbr(1,1:n))
x = SUM_SCATTER( -flux, x, nbr(2,1:n))
!等价于:
DO i = 1, n
　　x(nbr(1,i)) = x(nbr(1,i)) + flux(i)
　　x(nbr(2,i)) = x(nbr(2,i)) - flux(i)

inum(1:n) = MAX (iend(1:n)-ibeg(1:n)+1, 0)
ibeg_new(1:n) = SUM_PREFIX(inum(1:n)) + 1
iend_new(1:n) = ibeg_new(1:n)+inum(1:n)-1
!向左移动数据