# [petsc-users] sieve-dev Data shared between points in a Sieve DAG

Chris Eldred chris.eldred at gmail.com
Wed Jul 25 13:07:33 CDT 2012

```Lets consider the mesh from "Flexible Representation of Computational
Meshes" on the LHS of figure 2. (0,1) (0,2) (0,3) and (0,4) are vertices;
(0,5), (0,6), (0,7), (0,8) and (0,9) are edges; (0,10) and (0,11) are
cells. My field would be defined as (for example):

field ( (0,5) ; (0,10) ) = 1.0
field ( (0,6) ; (0,10) ) = 2.0
field ( (0,7) ; (0,11) ) = 1.3
etc.

Does that make sense?

On Wed, Jul 25, 2012 at 11:57 AM, Matthew Knepley <knepley at gmail.com> wrote:

> On Wed, Jul 25, 2012 at 12:52 PM, Chris Eldred <chris.eldred at gmail.com>wrote:
>
>> The closure operation makes sense, but what I want is something a little
>> different.
>>
>> I have a field that is defined as follows:
>> field(edge,cell) = blah
>> ie it really lives on the union of cells and edges (or vertex/edges,
>> cells/vertexs, etc.)
>>
>
> We need to make the language more precise. The union of the cell and edge
> is what
> closure would give you.
>
>
>> Is this something that can be defined using DMComplex and Sections?
>
>
> I cannot understand from this explanation. Can you give a small example?
>
>   Thanks,
>
>      Matt
>
>
>> On Wed, Jul 25, 2012 at 11:39 AM, Matthew Knepley <knepley at gmail.com>wrote:
>>
>>> On Wed, Jul 25, 2012 at 11:23 AM, Chris Eldred <chris.eldred at gmail.com>wrote:
>>>
>>>> I was wondering if it was possible to have fields that are shared
>>>> between points in a sieve DAG:
>>>>
>>>> For example, I would like to have data that is connected to both an
>>>> edge and a cell (instead of just tied to a Section). Consider a cell with
>>>> three edges (ie a triangular cell).
>>>>
>>>> Before I was just using a length 3 array attached to the cell with the
>>>> convention that the ordering of the array matched the ordering of the edge
>>>> list associated with the cell. Now, I would like an implementation that
>>>> does not assume anything about the ordering of the edge list (since I am
>>>> getting that from cones/supports).
>>>>
>>>
>>> I think what you want is the Closure operation. The closure of a cell
>>> will give you all the unknowns on its edges and vertices.
>>> Does that make sense?
>>>
>>>   Thanks,
>>>
>>>      Matt
>>>
>>>
>>>> Thanks,
>>>> -Chris Eldred
>>>>
>>>> --
>>>> Chris Eldred
>>>> DOE Computational Science Graduate Fellow
>>>> B.S. Applied Computational Physics, Carnegie Mellon University, 2009
>>>> chris.eldred at gmail.com
>>>>
>>>
>>>
>>>
>>> --
>>> What most experimenters take for granted before they begin their
>>> experiments is infinitely more interesting than any results to which their
>>> -- Norbert Wiener
>>>
>>
>>
>>
>> --
>> Chris Eldred
>> DOE Computational Science Graduate Fellow
>> B.S. Applied Computational Physics, Carnegie Mellon University, 2009
>> chris.eldred at gmail.com
>>
>
>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> -- Norbert Wiener
>

--
Chris Eldred