dolfin team mailing list archive

[Nuno David Lopes <ndl@xxxxxxxxxxxxxx>]

>Anders Logg
>Mon, 28 Jan 2008 02:00:43 -0800
>>On Fri, Jan 25, 2008 at 10:55:27AM -0500, Jake Ostien wrote:
>> I have a question about general usage of SubDomains.  I have a problem 
>> where I would really like to partition a domain (via some criterion) 
>> into 2 sub domains, and then assemble the global system as two separate 
>> assemblies over the sub domains.  The context here is for plasticity, 
>> initially I have a domain that is elastic but evolves such that there 
>> are two regions (elastic + plastic).  I am currently not dealing with 
>> this in a very elegant manner, and I was hoping that if I could somehow 
>> generate an elastic sub domain and a plastic sub domain, I could more 
>> efficiently assemble.  Does that sound possible currently, or could I 
>> add something like that in?  Eventually I think we'd like to extend the 
>> concept to assembly over facets on the boundary of the elastic/plastic 
>> interface as well, but this might be a good first step.
>> 
>> Jake

>You can define a form as a sum of contributions from different
>subdomains, for example:

>dx0 = Integral("cell", 0)
>dx1 = Integral("cell", 1)  

>a = v*u*dx0 + dot(grad(v), grad(u))*dx1

>This gives two terms, one of which will be used in subdomain 0 and the
>other in subdomain 1.

>Subdomains can be specified in DOLFIN by creating a subclass of
>SubDomain and overloading the inside() function, or by specifying a
>MeshFunction<uint> over the cells of the mesh.

>You can also have integrals over arbitrary facets of the domain, like
>for example the boundary between your two subdomains. You can have
>several such integrals:

>  ds0 = Integral("exterior facet", 0)
> ds1 = Integral("exterior facet", 1)
>  ds2 = Integral("exterior facet", 2)

>  dS0 = Integral("interior facet", 0)
> dS1 = Integral("interior facet", 1)
>  dS2 = Integral("interior facet", 2)

>-- 
>Anders


But how could we link the subdomains markers defined in a MeshFunction 
with the variational form in the cpp.
Example:

I have in a "Foo.form"  something like:
-------------------------------------------------------------------
P1=FiniteElement("Lagrange","tetrahedron",1)

f=Function(P1)

dx0 = Integral("cell", 0)
dx1 = Integral("cell", 1)  

a = f*v*u*dx0 + dot(grad(v), grad(u))*dx1
------------------------------------------------------------------
and in "main.cpp" something like
----------------------------------------------------------------------------------------------------------
MeshFunction<unsigned int> b_subdomains(mesh,"b_subdomains.xml");
//Boundary subdomain markers

MeshFunction<unsigned int> v_subdomains(mesh,"v_subdomains.xml");
//Volume subdomain   (0 and 1) markers

Function f(mesh,10.0);
FooBilinearForm a( f );//constructors for finite element form's (Problem here)
-----------------------------------------------------------------------------------------------------------
I'm missing something...

Shouldn't 
FooBilinearForm a( f );
be replaced by  something like
FooBilinearForm a( f ,v_subdomains);  ?


-- 
Nuno David Lopes