[Dune] How children which are copies of their father handled in DUNE?

[Markus Blatt]

Hi Raffael,

On Thu, Apr 03, 2014 at 09:30:49AM +0000, Casagrande  Raffael wrote:
> I have problems to understand how entities which are exact copies of their father are being dealt with in the context of leaf views. In particular consider the following 1D hierarchical grid:
> 
> (a)-------------(i)------(b)    level 0
> (c)------(d)----(j)               level 1
> 
> where (a), ..., (j) denote the nodes of the grid. As far as I understand the following is true:
> - node (j) is a copy of it's father (i).
> - The leaf view consists of nodes (c), (d), (i), (j), (b) since node (i) belongs to a codim=0 leaf entity.
> - The id of node (i) == id of node (j) (global id set)
>
> Is this correct?

Yes, that is correct.
 
> If so there are a few things which are very unclear to me:
> - is the leaf index of node (i) the same as the leaf index of node
> (j) ? I think this should be the case because of [1] Def. 25, but
> the dune class documentation seems to suggest the opposite (and is
> not very clear about this).

No that is the case. The index set (leaf index map in Def. 25), is
a mapping from zero to the number of entities of this codimension,
reference element and process number (Def. 25 clause 1). Clause 2 only
holds for copies of entities that are part of the leaf view. In this
case no matter whether you retrieve the node from the right or left
element it will be mapped to the same index.

Which part of the documentation are you referring to?
http://www.dune-project.org/doc/doxygen/html/classDune_1_1IndexSet.html#_details
which reads
"The index map $m$ has the following properties:

    It is unique within the subsets $E_g^c$, i.e. for any
    $e,e^\prime\in E_g^c$ we have $e\neq e^\prime \rightarrow m(e)\neq
    m(e^\prime)$."

I guess we might not have defined what equaltiy of entites
means... Please let us know how we can improve this.

> - How is the size() method of the leaf view defined for nodes, is leafView().size(nodes) == 5 or == 4?
> - How is the size() method of the leaf index set defined for nodes? is leafView().indexSet().size(nodes) == 5 or == 4?

Should be 4 for both, to let users allocate containers of the correct
size.

Markus
-- 
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