Re: [Libmesh-users] Given a physical (or reference, outside of domain) point, which element does it belong to?

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

On Wed, 15 Nov 2017, Zack Vitoh wrote:

> I think
> http://libmesh.github.io/doxygen/classlibMesh_1_1SubdomainPartitioner.html#details
>
> May help, but still not sure if this is the best approach

No, that's unrelated to what you want to do.

The class you should look up is
https://libmesh.github.io/doxygen/classlibMesh_1_1PointLocatorBase.html

and the method you want to look at in the library is
"sub_point_locator" in MeshBase.

The default PointLocatorTree implementation uses a binary/quad/oct
tree (in 1/2/3D) and will give you a logarithmic search time.

If you have *really* large meshes, then you might be able to come up
with a faster custom locator (e.g. if you know your quadrature points
will be in an element touching the current element, then you could use
Elem::find_point_neighbors() to get all those elements, and check just
those for an O(1) search with a lousy constant), but the point locator
will probably be the best way to get started simply.
---
Roy

> On Tue, Nov 14, 2017 at 10:17 PM, Zack Vitoh <jan...@gm...> wrote:
>
>> I could loop over (a subset of) all elements in the mesh, but is there a
>> function within a class that achieves this (possibly more efficiently?)
>>
>> Thanks!
>>
>> PS: I am trying to incorporate a "nonlocal quadrature rule" where the
>> nonlocal quadrature involves points outside of the current element.  If any
>> other advice can be provided (e.g. specific classes/functions to look at)
>> to this end, I'd appreciate it, as I am going about this in what feels to
>> be a hackish, wrong way.
>>
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