Oh weird.  This is highly non-intuitive (to me). I think `i` is misnamed as the iteration order then.  I was under the assumption that `i` is reserved for the index in the mesh (how you are using `ve_idx`).  Moreover, idx to me is plural and an `_` is a subscript so I read this as "the volume element at the index i."  I think we need to stay away from using `ve` and `idx` / `i` in the same variable name.