[数值问题] 输出数据全部为零

subroutine rhouv(f,rho,u,v,cx,cy,n,m)
real f(0:8,0:n,0:m),rho(0:n,0:m),u(0:n,0:m),v(0:n,0:m),cx(0:8),cy(0:8)
integer :: i, j, k
real :: ssum, usum, vsum
    do j=0,m
        do i=0,n
            ssum = 0.0
            usum = 0.0
            vsum = 0.0
            do k=0,8
                ssum = ssum + f(k,i,j)
                usum = usum + f(k,i,j)*cx(k)
                vsum = vsum + f(k,i,j)*cy(k)
            !print*,vsum,usum      ! 可以输出数据
            end do
            !print*,ssum,usum,vsum ! 输出数据全部为零
            rho(i,j) = ssum
            if (ssum > 0.0) then
                u(i,j) = usum / ssum
                v(i,j) = vsum / ssum
            else
                u(i,j) = 0.0
                v(i,j) = 0.0
            end if
            !print*,u(i,j),v(i,j)
        end do
    end do