[Dune] How to set boundary ids

[Oliver Sander]

Hi Andreas, hi Martin!
I do not think that this is a good idea, because:
- The GridFactory interface gets a lot more complicated
- In your proposal, the grid factory returns a mapping that does
  a renumbering from level<0> index to insertion order.
  This mapping could also be a part of the grid implementation
  and remain invisible to the user.  Since we are only talking
  about level 0 the time overhead should not be a problem.

Concerning your postscriptum: Preferably we do not prescribe
any order.  This is easiest for the user, and if the actual grid
needs the entities in a specific ordering the grid factory can
cache elements and vertices.  This is how it is done in UGGrid.

--
Oliver

Andreas Dedner schrieb:
> Hi,
> a second suggestion for handling data attached to the initial grid:
>
>    For a grid implementation preserving the order of insertion might be
>    difficult and might require wrapping the level<0> index set of the
>    grid even after grid creation. Alternatively the grid factory could
>    provide a mapping from level<0> index to insertion order.
>    Possible interface:
>    class Factory < G > {
>      void insert(entity) {...}
>      void create() {...}
>      View view() {...}
>      int operator[](const Entity<0>& en) { return insertionOrder; }
>      int operator[](const Entity<dim>& vtx) { return insertionOrder; }
>      int operator[](const Intersection& bnd) { return insertionOrder; }
>      G* finalize() { return grid; }
>    };
>    Note that create() does not return the grid and does not finalize the
>    Factory. The old method createGrid() could still be available and
>    would be equivalent to calling create(); finalize();
>
> Greetings
> Andreas and Martin
>
> PS:
>    do we specify the order in which vertices, elements, and boundary
>    segments are added to the Factory, e.g., first all vertices and
>    then the elements, or at least all that all vertices needed for the
>    inserted element have already been inserted?
>
>
>
> Oliver Sander wrote:
>> Dear Dune!
>> As far as I know the question of who sets boundaryIds and how
>> is still unsettled.  Two days ago Peter, Christian, Benedikt and me
>> discussed this issue again.  We came up with a solution that was
>> acceptable to all four of us and combines (in our view) a consistent
>> interface with ease of use.
>>
>> We propose that boundary ids should be consecutive and starting
>> from zero.  The user can influence the ordering by calling insert-
>> BoundarySegment in the desired order.  The second argument
>> (the segment geometry) will be made optional such that the user can
>> specify boundary segment orderings and still leave the geometry to the
>> implementation.I have described the solution in some more detail in
>> Sections 4.4 and 4.5 of the grid-howto.
>>
>> We propose that the behavior described there be part of the official
>> Dune grid interface.  Please read it carefully and give us feedback.
>>
>> Yours,
>> Oliver
>>


-- 
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