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<p>Hi Martin,</p>
<p>for example, in my code, I have created a "sorted leaf view". This view allows me to iterate over the elements in a way that two consecutive elements are very close spatially. This property speed up the interpolation of a discrete function. (I know that
is not a very clear explanation<img class="EmojiInsert" alt="😊" style="vertical-align: bottom;" src="cid:e1cfbc32-07d0-47c9-be31-597f1da4d1e8">)</p>
<p><br>
</p>
<p>Creating this custom view comes to a cost, therefore is better to do it only once. This is possible because the sorting depends only on the topology of the mesh and not on the actual coordinates. <span style="font-size: 12pt;">Obviously, I have to avoid
to traverse a grid looking for the element ids otherwise all the speed up gain is completely lost.</span></p>
<p><br>
</p>
<p>The only way that I know is to store entity seeds while in the past I was storing entity pointers. I don't see any other way to have direct access to an entity within DUNE. So I think that it is necessary to assure consistency of the entity seed also after
a grid modification which doesn't change the topology of the grid. </p>
<p><br>
</p>
<p>It makes sense that the behaviour of entity/geometry is not enforced by the interface after a grid modification. For example, a caching process can be involved and if you move the grid they still refer to the old grid. </p>
<p><br>
</p>
<p>So the bottom line is that the interface should assure that entity seed are always valid (which now is indeed the case for GeometryGrid).</p>
<p><br>
</p>
<p>Cheers,</p>
<p>Marco </p>
<p></p>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Martin Nolte <nolte@mathematik.uni-freiburg.de><br>
<b>Sent:</b> 03 March 2016 19:39<br>
<b>To:</b> dune@dune-project.org<br>
<b>Subject:</b> Re: [Dune] Info GeometryGrid and entity seed</font>
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<div class="PlainText">Hi Marco,<br>
<br>
as I don't know your exact application, I will hardly be a good advisor. <br>
Therefore, I stick to the interface.<br>
<br>
The answer to your question is: Yes, there is another way. You can store the <br>
ids, e.g., in a std::set. They are guaranteed to be persistent over grid <br>
modification. On the downside: You need to traverse the grid to get the entities <br>
(or entity seeds) back.<br>
<br>
That said, as long as you stick to GeometryGrid and keep a keen eye on changes, <br>
you should be safe reusing the entity seeds after modifying the coordinate function.<br>
<br>
Actually, I would not even count on the behavior of an entity. Assume you have <br>
an entity e and then modify the coordinates. What will be the result of <br>
e.geometry() afterwards? Right now, it depends on whether you obtained the <br>
geometry before modifying the coordinate function or not. If you did, you will <br>
get the old geometry, otherwise the new one. Please note that this behavior <br>
conforms to the specification, as you are not allowed to keep entities over any <br>
kind of grid modification.<br>
<br>
Best,<br>
<br>
Martin<br>
<br>
On 03/03/2016 07:48 PM, Agnese, Marco wrote:<br>
> Hi Martin,<br>
><br>
> thank you for the answer.<br>
><br>
><br>
> Right now I am constructing the entity from the entity seed after the<br>
> GeoemtryGrid has been moved and it works perfectly fine.<br>
><br>
><br>
> But what is the alternative? I need to store some entities (or a pointer/ an<br>
> iterator to them) and retrieve them after the grid has been moved. I thought the<br>
> only way is to save the relative entity seed. Is there another way to do it?<br>
><br>
><br>
> Cheers,<br>
><br>
> Marco<br>
><br>
><br>
><br>
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-- <br>
Dr. Martin Nolte <nolte@mathematik.uni-freiburg.de><br>
<br>
Universität Freiburg phone: +49-761-203-5630<br>
Abteilung für angewandte Mathematik fax: +49-761-203-5632<br>
Hermann-Herder-Straße 10<br>
79104 Freiburg, Germany<br>
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