dolfin team mailing list archive

[Kent-Andre Mardal <kent-and@xxxxxxxxx>]

On Sat, 2008-06-28 at 20:55 +0200, Johan Hake wrote:
> Hello!
> 
> I tried to compile an advection diffusion form using Streamline Upwind Petrow 
> Galerkin stabilazing method, similar to the one introduced in DOLFIN 0.6.4. 
> Using 3 dimensional and first degree Lagrange elements, FFC/g++ chokes when 
> the produced code is compiling. It wont finish compile... Is this a known 
> problem and a limitation of FFC/g++?
> 
> In PyCC I use DOLFIN to assemble the same system matrix, but instead of using 
> one form for the whole system I split the form into at least 4 different 
> forms. These compiles smoothly and after I have assembled the matrices I just 
> add them together. 
> 
> This approach is not possible using the present DOLFIN linear algebra 
> interface, as sum of matrices is not supported. Is this something we want for 
> the future? 
> 
> Johan

If the matrices come from the same dof_map one "should" be able to add
to matrices together (and if not I guess you
would not add them toghether). The problem is that the matrices
themselves do not know what their created from.  

However, one could write a function 

matrix_add(mesh, dof_map, A, B, C); 

That does the trick in terms of the tabulate_dofs funcition in dof_map
and the get, add functions in GenericMatrix. 

Kent