[dune-functions] [Dune-functions-commit] [Commit] dune-functions - e7abafb: Add protocol for Aachen meeting

[Christian Engwer]

Hi Carsten,

> this is a little surprising to me since we already discussed this
> and decided differently. Unfortunately removing the 'is consecutive'
> guarantee makes the whole multi index concept useless. Without this
> guarantee the multi index is just some unique id equally usefull
> than a hash.

we realized that the whole multi-index is even with the zero-starting
useless. The main reason for not writing consecutive is that Steffen
doesn't consider the GeometryTypeIndex to be consecutive. A) because
we can have GeometryTypes with 0 DOFs and B) because the
GeometryTypeIndex contains entries where no GeometryType is assigned
to.

> If you (in contrast to what we discussed) really need non-consecutive
> indices it would be nice if you could give a short explanation and
> come up with some replacement. Otherwise the only thing you can
> do based on the interface is looping over all dofs and put them into
> some (unordered)map<MultiIndex,SomeUsefullIndex>.

No Carsten. You can do all the things we are doing now, iff the exact
semantics are defined. Currently we store the GeometryTypeIndex, which
is non-consectutive, but this is not the issue. The issue is that
permutations of multi-index entries usually swap two digits, but in
the case of entities they swap the pair or GeometryTypeIndex and
EntityIndex with the other entry. This is not the thing you expect
when talking about multi-indices, but it is what you expect when
talking about about where to block your information. In this case it
doesn't mater if you use the GeoetryTypeIndex, or some compressed
version. You need to know about the exact semantics and if you know
this possible non-consecutive indices are not a real problem. An other
example is, at least in our current design, if you have a
multi-physics problem. Then the locak tree contains all spaces for all
sub-domains, but only the correct sub-tree is in a bound state. This
is necessary in order to keep the C++ types fixed. In this situation
you again have non-consecutive indices, because some of the entries in
your tree don't contain any DOFs.

I hope this explains a little bit what the issues in our opinion are.

Ciao
Christian

> Best,
> Carsten
> 
> Am 26.03.2014 10:00, schrieb Christian Engwer:
> > Hi Carsten,
> > 
> > We discussed this yesterday. There are many open questions regarding
> > the backend interface and the multi index is one of them. In any case
> > we have to specify the exact semantics of different versions of multi
> > indices and this might them include that they are zero starting.
> > 
> > Christian
> > 
> > 
> > On 25. März 2014 21:54:37 MEZ, "Carsten Gräser" <graeser at mi.fu-berlin.de> wrote:
> >> Hi Steffen,
> >> didn't we decide that the global multi
> >> indices should always be consecutive?
> >> If not, we may also add a method to
> >> check if a prefix does appear in any
> >> index.
> >>
> >> Best,
> >> Carsten
> >>
> >> On 25. März 2014 19:19:23 MEZ, "Steffen Müthing"
> >> <muething at dune-project.org> wrote:
> >>> New commit, appeared at Tue Mar 25 19:19:23 2014 +0100
> >>> as part of the following ref changes:
> >>>
> >>>    branch refs/heads/master    updated from 3289b50 -> e7abafb
> >>>
> >>> Browsable version:
> >>> http://cgit.dune-project.org/repositories/dune-functions/commit/?id=e7abafbf4a2892734c598c4984a633d4709a1cc2
> >>>
> >>> ======================================================================
> >>>
> >>> commit e7abafbf4a2892734c598c4984a633d4709a1cc2
> >>> Author: Steffen Müthing <muething at dune-project.org>
> >>> Da
> 	
> 
> -- 
> Prof. Dr. Carsten Gräser
> Freie Universität Berlin
> Institut für Mathematik
> Arnimallee 6
> 14195 Berlin, Germany
> phone: +49 30 838 75349
> fax  : +49 30 838 54977
> email: graeser at mi.fu-berlin.de
> URL  : http://page.mi.fu-berlin.de/graeser
> 
> _______________________________________________
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-- 
Prof. Dr. Christian Engwer 
Institut für Numerische und Angewandte Mathematik
Fachbereich Mathematik und Informatik der Universität Münster
Einsteinstrasse 62
48149 Münster

E-Mail	christian.engwer at uni-muenster.de
Telefon	+49 251 83-35067
FAX		+49 251 83-32729