Re: [Libmesh-users] Neighbors of element

[Roy S. <roy...@od...>]

On Wed, 21 Oct 2020, John Peterson wrote:

> On Wed, Oct 21, 2020 at 12:39 PM Laura Scarabosio <
> lau...@gm...> wrote:
>
>> I would like to find the neighbors of a mesh element including those that
>> share a vertex only with that element, not only those that share an edge
>> with the element (so the method neighbor_ptr does not help). Is there a way
>> to do this?
>
> This information (point neighbors) isn't stored in the Mesh by default
> since it isn't needed in most cases. You may want to look into calling
>
> MeshTools::build_nodes_to_elem_map()
>
> which builds a data structure which associates, to each Node, a vector of
> connected Elem ids. It's a bit expensive to build this map, so best to do
> it only once and then use it each time you need to find a point neighbor.

We do also have Elem::find_point_neighbors() - not as efficient on CPU
if you need to do a lot of lookups, but it avoids building the map.
---
Roy