dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

Then you're out of luck, for now. There is currently no way to
integrate over two meshes at once. All functions that you integrate
together must be defined on the same mesh (but they don't have to be
in the same finite element space).

So you need to define both functions on the same mesh (the fine mesh).

/Anders

On Wed, Nov 09, 2005 at 03:34:38PM +0100, hetzel.devel@xxxxxx wrote:
> 
> Hi Johan,
> I don't want to create two matrices.
> My bilinearform is defined like a(u,v), where u is a vector of u1 and u2. The same for v.
> What I now need is the give the first component of the Vector u and  v another mesh then the second.
> I need to solve a modified version of the Navier-Stokes PDE.
> The reason is, that the first component is used to calculate a pressure. This needs to be calculated quite exactly so I need a mesh with many nodes.
> The second component is the hight of my oil-thickness. But this mesh needs to be coupled with a quite rough mesh, of another calculation. Therfore I only have some nodes to work with.
> The matrix will look like this
> a=[ A B ]
>     [ C D ]
> With a look to the matrix there is no Problem to calculate the upper left corner A (2000x2000) and the lower right D (20x20), but I also need the coupling C and D so the 20x2000 and 2000x20 matrices.
> 
> /Haiko
> 
> 
> Discussion of DOLFIN development <dolfin-dev@xxxxxxxxxx> schrieb am 09.11.05 15:02:06:
> > 
> > On Wed, Nov 09, 2005 at 10:48:37AM +0100, hetzel.devel@xxxxxx wrote:
> > > 
> > > Hi,
> > > I'm having two functions say u1 und u2 and two test functions v1 and v2. At the moment I'm using the "Vector Lagrange" Functions to declare u and v as a vector.
> > > 
> > > I would like to solve my PDE with u1 and v1 defined on mesh1 (approx. 2000 nodes) and u2 and v2 defined on a different mesh2 (approx. 20 nodes). I would like to get a 2020x2020 matrix. Both meshes will be contain exectly the same area.
> > > Is there a change to declare the bilinearform in such a manner?
> > > 
> > > /Haiko
> > > 
> > 
> > Hi Haiko,
> > 
> > A form is not connected to a specific mesh, so it's perfectly ok to
> > assemble the same bilinear form on two different meshes. But then you
> > would get two different matrices. Why do you want the result in the
> > same matrix? Isn't it ok to get matrix A1 (2000x2000) corresponding to
> > the first mesh and matrix A2 (20x20) corresponding to the second mesh?
> > 
> >   Johan
> > 
> > _______________________________________________
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> 
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-- 
Anders Logg
Research Assistant Professor
Toyota Technological Institute at Chicago
http://www.tti-c.org/logg/