[petsc-dev] PetscSection

Blaise A Bourdin bourdin at lsu.edu
Sat Nov 10 13:55:50 CST 2012

On Nov 10, 2012, at 1:44 PM, Matthew Knepley <knepley at gmail.com>

> On Sat, Nov 10, 2012 at 2:33 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>> On Sat, Nov 10, 2012 at 1:26 PM, Matthew Knepley <knepley at gmail.com> wrote:
>>> I do not understand. Codim 0 and 1 are handled in an identical way.
>> The user doesn't do the same thing with them. Your data structure treats
>> them the same way (though I'm not sure how you distinguish between a tet and
>> a quad if both are "height 0" and you don't store intermediate levels), but
>> that seems like an implementation detail to me.
> Yes, I agree that they are different geometrically, and in PyLith we
> make Labels to
> distinguish, which I think is the right way.

I actually disagree they may or may not be treated different. It all depends on what you want to do. If all you are interested in is computing integrals, elements are elements are elements. There is no fundamental difference between computing integrals over surfaces or volumes. And the user already needs to keep track of the polynomial order, interpolation type, integration type etc on a per element or per block of elements basis, right? If you cache the values of your FE basis functions at integration points and integration weights, integrating over a surface or an element is _exactly_ the same thing.

>>> I am not against some convenience interface for dim/co-dim, however it
>>> would
>>> just be implemented by making a label, since we have many equivalent
>>> structural
>>> things which would map to it.
>> Fine, I care much more about conceptual simplicity in the interface. I think
>> adoption will be higher if 95% of users don't see the word "stratum".
> Note that this will have to be set explicitly somehow, since you cannot "tell"
> from the DAG that something has a given dimension/co-dim.

You can also not say anything about the element type from the DAG either. Is this a problem? Of course no. My point is that if a mesh has cells with different codimension, this information is something in the description from which the DM was created, and was probably imported somewhere in an IS, right?


Department of Mathematics and Center for Computation & Technology
Louisiana State University, Baton Rouge, LA 70803, USA
Tel. +1 (225) 578 1612, Fax  +1 (225) 578 4276 http://www.math.lsu.edu/~bourdin

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