Re: [Libmesh-devel] Multiple subdomain IDs?

[David K. <dkn...@se...>]

On 04/08/2013 11:59 AM, Roy Stogner wrote:
>
> On Mon, 8 Apr 2013, David Knezevic wrote:
>
>> I have a use-case where it'd be helpful to store multiple subdomain IDs
>> on elements (similar to what we do for boundary IDs now).
>>
>> The first thing that comes to mind is changing Elem to store a
>> std::set<subdomain_id_type>, would that be of interest in general?
>
> Opposing that would probably be of interest in general.  We typically
> have sizeof(subdomain_id_type)==2; squeezing even a couple pointers in
> there would lead to megabytes of extra RAM use on large problems. The
> boundary is generally a "cheaper" case since a problem with a million
> elements is likely to only have ~50,000 boundary elements, and only a
> fraction of those are on the coarse grid.

Yep, agreed. I figured that since we have multiple IDs in the boundary 
case it might be of interest in the subdomain case too. But yes, the 
extra memory for the boundary IDs isn't such a big deal...

I can make user code (as Ben suggested) that'll work for me case with 
the single subdomain setup (I might do some bitwise AND'ing of subdomain 
IDs with "masks")

David