[Dune] Info GeometryGrid and entity seed

[Martin Nolte]

Hi Marco,

as I don't know your exact application, I will hardly be a good advisor. 
Therefore, I stick to the interface.

The answer to your question is: Yes, there is another way. You can store the 
ids, e.g., in a std::set. They are guaranteed to be persistent over grid 
modification. On the downside: You need to traverse the grid to get the entities 
(or entity seeds) back.

That said, as long as you stick to GeometryGrid and keep a keen eye on changes, 
you should be safe reusing the entity seeds after modifying the coordinate function.

Actually, I would not even count on the behavior of an entity. Assume you have 
an entity e and then modify the coordinates. What will be the result of 
e.geometry() afterwards? Right now, it depends on whether you obtained the 
geometry before modifying the coordinate function or not. If you did, you will 
get the old geometry, otherwise the new one. Please note that this behavior 
conforms to the specification, as you are not allowed to keep entities over any 
kind of grid modification.

Best,

Martin

On 03/03/2016 07:48 PM, Agnese, Marco wrote:
> Hi Martin,
>
> thank you for the answer.
>
>
> Right now I am constructing the entity from the entity seed after the
> GeoemtryGrid has been moved and it works perfectly fine.
>
>
> But what is the alternative? I need to store some entities (or a pointer/ an
> iterator to them) and retrieve them after the grid has been moved. I thought the
> only way is to save the relative entity seed. Is there another way to do it?
>
>
> Cheers,
>
> Marco
>
>
>
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-- 
Dr. Martin Nolte <nolte at mathematik.uni-freiburg.de>

Universität Freiburg                                   phone: +49-761-203-5630
Abteilung für angewandte Mathematik                    fax:   +49-761-203-5632
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