dolfin team mailing list archive

[mspieg <mspieg@xxxxxxxxxxxxxxxxx>]

Thanks Garth,

On Jul 15, 2009, at 10:44 AM, Garth N. Wells wrote:

> mspieg wrote:
> > Hi All,
> >    I think there is a bug when trying to read a MeshFunction from  
> > a file that was generated on a SubMesh.  I've attached some python  
> > based on the SubMesh demo, that demonstrates the problem.  I think  
> > the issue is that there is an extra MeshFunction embedded in a  
> > SubMesh to describe the "global vertex indices" that gets read  
> > instead of the intended mesh-function.
>
> It might be a while before anyone gets to this. We hope to have a  
> new, simple to use bug tracking system (i.e. not Bugzilla) in place  
> soon to keep track of these types of issues, especially since they  
> tend to be forgotten while everyone is on holiday.

That would be good.  I can work around this easily enough at the  
moment (if I just strip out the unwanted MeshFunction from the file  
everything works fine).  If I don't see a fix, I'll post something on  
the new bug tracking system when it's in place.
> > On a related note, it's easy enough to extract a SubMesh from a  
> > larger Mesh using a MeshFunction, but what is the best way to  
> > extract just the piece of a discrete function on the SubMesh, when  
> > the Function is originally defined for a Function Space on the  
> > larger mesh. (does this make sense?)
> > These issues arise from a multiphysics problem that I'm working  
> > with overlapping domains  where I basically want to solve an  
> > embedded porous media problem on a subdomain of a larger stokes  
> > flow (this is slightly different from the fluid-structure demo  
> > where the two domains only share a boundary.)
>
> Kent has been working on something like this. Have you looked at
>
>   demo/function/restriction

I started to look at this...A couple of questions/issues

1) at the moment restriction only takes MeshFunction<bool> whereas  
SubMesh takes (MeshFunction<uint>,uint) which allows multiple  
subdomains.  It might be nice if these two had similar interfaces  
particularly since I think it makes more sense to use SubMesh to  
apply boundary conditions on the subdomain.

2) At the moment restriction seems to mainly apply to the function  
space, not the function (i.e. the demo just creates a new function on  
the restricted function space, not extracts a restricted function  
from the larger space).  I suspect this wouldn't be too hard to do,  
but it's not entirely obvious what the best way to do this would  
be...a nice interface would be similar to FunctionSpace.restriction 
()  something like F=Function(V), F_restricted=F.restriction 
(MeshFunction<?>)

3) I have no idea how to handle this in parallel (but a lot of these  
issues are related to local<->global mappings and maybe something can  
be cleanly designed for all of these problems)

Like I said, I can work around all of this at the moment, but it  
would be useful to think through the best way to deal with these  
sorts of embedded multi-physics problems.

Thanks again
marc


> ?
>
> Garth
>
> > All help greatly appreciated as always
> > cheers
> > marc
> > p.s. all current dev repositories
> > p.p.s. another official release would be great...a lot has changed  
> > since 2009-04
> > --------------------------------------------------------------------- 
> > ---
> > ----------------------------------------------------
> > Marc Spiegelman
> > Lamont-Doherty Earth Observatory
> > Dept. of Applied Physics/Applied Math
> > Columbia University
> > http://www.ldeo.columbia.edu/~mspieg
> > tel: 845 704 2323 (SkypeIn)
> > ----------------------------------------------------
> > --------------------------------------------------------------------- 
> > ---
> > _______________________________________________
> > DOLFIN-dev mailing list
> > DOLFIN-dev@xxxxxxxxxx
> > http://www.fenics.org/mailman/listinfo/dolfin-dev

----------------------------------------------------
Marc Spiegelman
Lamont-Doherty Earth Observatory
Dept. of Applied Physics/Applied Math
Columbia University
http://www.ldeo.columbia.edu/~mspieg
tel: 845 704 2323 (SkypeIn)
----------------------------------------------------