[Dune-devel] idset.subId() only for codim=0?

[Carsten Gräser]

Hi,

Am 22.02.2016 um 13:20 schrieb Steffen Müthing:
> Hi,
> 
>> Am 22.02.2016 um 12:27 schrieb Jö Fahlke <jorrit at jorrit.de>:
>>
>> Am Mon, 22. Feb 2016, 11:54:42 +0100 schrieb Aleksejs Fomins:
>>> Date: Mon, 22 Feb 2016 11:54:42 +0100
>>> From: Aleksejs Fomins <aleksejs.fomins at lspr.ch>
>>> To: "dune-devel at dune-project.org" <dune-devel at dune-project.org>
>>> Subject: [Dune-devel] idset.subId() only for codim=0?
>>
>>> Can somebody please explain what is the motivation behind idset.subId(Entity, index, codim) in dune-grid being restricted to codim=0 entities?
>>>
>>> I was trying to find the Ids of the vertices of a face in 3D.
>>
>> Well, I think you are the first one to request that feature.  And I think that
>> if you require that functionality in general for all grids, most grids would
>> have to store *a lot* more connectivity information than they are doing
>> already to implement it.  So that may be the reason why this has never been
>> part of the interface.
> 
> yes, AFAIK that’s basically the reason - for the same reason, there is only an
> index_set.subIndex() and an entity.subEntity() for codim 0 entities.
that's not correct: On the 2010 developer meeting we decided that
the subIndex() method should also be added for other codimensions:

  http://users.dune-project.org/projects/dune-dev-meeting-201/wiki/Protokoll#subIndex-interface

The reason for this is that otherwise there's no way to get the
embedding of subentities without doing coordinate comparisons.
See also the corresponding flyspray task:

  https://gitlab.dune-project.org/flyspray/FS/issues/818

Unfortunately, while trying to fix this one

  https://gitlab.dune-project.org/flyspray/FS/issues/1709

for 2.4, it turned out, that this method seems to be broken
(i.e. compilation fails). Since noone ever noticed this it
was postponed to 3.0.

Best,
Carsten


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