/p>
<div class="codehilite"><pre><span></span> --+---v---+---v---+---v--
   |       |       |
</pre></div>


<p>j+1   u   f   u   f   u   f
       |       |       |
     --+---v---+---v---+---v--
       |       |       |
  j    u   f   u   f   u   f
       |       |       |
     --+---v---+---v---+---v--
       |       |       |
 j-1   u   f   u   f   u   f
       |  i-1  |   i   |  i+1</p>
<p>The differentiation range is [2:size(f,dim=1)-1,2:size(f,dim=2)-1], so 1
 halo cell on each end needs to be set pri