[Dune-devel] Semantics of {ghost,overlap}Size

Fri Nov 8 09:10:30 CET 2013

Dear all,

since my name was mentioned, I would like to show my sincere interest in 
participating in such a smaller group. Although most interface decisions 
that I was part of proved to be shortsighted, I will do my best to give 
at least a good impression...

Kind regards
Bernd

On 11/07/2013 08:55 PM, Martin Nolte wrote:
> Hi Peter,
>
> to be honest, I am not sure how much can be achieved with a single 
> meeting.
>
> The idea originated from the observation that the topic "parallelism" 
> was carefully avoided on the last "big" developer meetings. It was my 
> impression that on the one hand "only" around 50% of the core 
> developers are interested in this feature, while on the other hand 
> there are some extremely interested users (e.g., Bernd who has 
> provided substantial contributions to parallel UG).
>
> I think such a smaller group focussing entirely on this topic might 
> achieve more progress. It goes without saying that the "real 
> decisions" must be made by a formal vote of all core developers.
>
> If there is enough interest in such a meeting, I suggest to set up a 
> page on the user wiki, so that we can collect the topics we're 
> interested in. We then might be able to judge the size of this thing. 
> We can always shorten the list, if it becomes too large. Given 
> interest, I would be prepared to organize such a meeting in (or near) 
> Freiburg.
>
> Best,
>
> Martin
>
>
>
> On 11/07/2013 08:22 PM, Peter Bastian wrote:
>> Dear all,
>>
>> clearly this has not been completely thought to the end once upon atime.
>>
>> I see that you need a specification of overlap for codim 0 and codim 
>> dim.
>>
>> Codim dim (vertices) is needed for standard overlapping DD methods.
>> I would define two vertices as connected if they are subentites of a 
>> common
>> codim 0 entity. With that Graph defined the distance ist clear.
>> Then of course the data decomposition is still with respect to codim 0
>> entites
>>
>> likewise two codim 0 entites are connected if they share an 
>> intersection.
>>
>> I am not sure whether the "overlap size" has any real application. In 
>> the numerical
>> methods it is usually not needed.
>>
>> I am in favor of a meeting. Do you think about small cosmetic changes 
>> or something
>> bigger? If it is bigger then we should also consider extensions due 
>> to hybrid
>> parallelism, i.e. multithreading.
>>
>>
>> -- Peter
>>
>> ----------------------------------------
>> Peter Bastian,
>> IWR, Universität Heidelberg,
>> INF 368, D-69120 Heidelberg
>>
>>> Am 07.11.2013 um 16:10 schrieb Martin Nolte 
>>> <nolte at mathematik.uni-freiburg.de>:
>>>
>>> Hi,
>>>
>>> actually, I wonder whether anybody uses these methods at all (except 
>>> for checking the return value for 0).
>>>
>>> Otherwise, I totally agree with Markus that semantics of the methods 
>>> are completely unclear:
>>> - They are not mentioned in the papers on dune-grid.
>>> - The documentation of the interface does not give a definition
>>>   (what is the size of a "region"? Why is this integral?).
>>> - The tests do not verify the result of these methods at all
>>>   (though it seems the information can be obtained by grid traversal).
>>>
>>> A mere hint in the documentation of YaspGrid is absolutely 
>>> insufficient.
>>>
>>> Implementation node: SPGrid only implements these methods for codim 
>>> 0, returning the number of elements in the corresponding partition. 
>>> Up to now nobody complained about this.
>>>
>>> Given the current status, we might just replace these methods by 
>>> capabilities like hasGhosts or hasOverlap.
>>>
>>> Anyway, in my opionion (as stated on the wish list for the developer 
>>> meeting) the parallel part of the dune-grid interface should be 
>>> revised in the near future. I think there are several points worth 
>>> discussion. I was already thinking about a "small" meeting of those 
>>> directly involved in the parallel interface (both on the user's and 
>>> on the developer's side). What do the others feel?
>>>
>>> Best,
>>>
>>> Martin
>>>
>>>> On 11/07/2013 11:39 AM, Andreas Dedner wrote:
>>>> Hi.
>>>> I've wondered about that as well and am thinking that the method 
>>>> really only
>>>> makes sense for codim 0 (where it the semantics seems clear enough).
>>>>
>>>> In DUNE everything boils down to codim 0 anyway (i.e. what leaf 
>>>> entities
>>>> are for example). So if I have an overlap of 2 codim 0 entities then
>>>> I would expect that the corresponding entities of higher 
>>>> codimension are
>>>> there
>>>> as well....
>>>>
>>>> Does anybody use that method for c>0?
>>>>
>>>> Best
>>>> Andreas
>>>>
>>>> PS: should these method be deprecated on the grid class?
>>>>
>>>>> On 07/11/13 10:33, Markus Blatt wrote:
>>>>> Hi,
>>>>>
>>>>> I recently looked at the documentation off these methodsbut this did
>>>>> not help me understand what they are doing. It reads "Return size of
>>>>> ghost region for a given codim on the leaf grid" but it is not clear
>>>>> to me what this size is.
>>>>>
>>>>> In the documentation of yaspgrid it says that size is the distance in
>>>>> graph, which is not really clearer. I assume that means the smallest
>>>>> path between any two entities on different borders of that
>>>>> region. Which still leaves the question open what the graph
>>>>> of an enitity set of a given codim is. The vertices are of course the
>>>>> codim entities. Seems like the edges would be the codim 1 entities 
>>>>> for
>>>>> elements and for all other entities with codim c the ones with 
>>>>> codim c+1.
>>>>>
>>>>> Is there a precise definition somewhere?
>>>>>
>>>>> Markus
>>>>
>>>>
>>>> _______________________________________________
>>>> Dune-devel mailing list
>>>> Dune-devel at dune-project.org
>>>> http://lists.dune-project.org/mailman/listinfo/dune-devel
>>>
>>> -- 
>>> 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
>>> Hermann-Herder-Straße 10
>>> 79104 Freiburg, Germany
>>>
>>> _______________________________________________
>>> Dune-devel mailing list
>>> Dune-devel at dune-project.org
>>> http://lists.dune-project.org/mailman/listinfo/dune-devel
>

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