dolfin team mailing list archive

["Garth N. Wells" <g.n.wells@xxxxxxxxxxxxxxx>]

Quoting Anders Logg <logg@xxxxxxxxx>:

> On Wed, Oct 05, 2005 at 03:41:33PM +0200, Garth N. Wells wrote:
> 
> 
> > I can't test big problems because BLAS mode has *huge* memory
> > requirements when using higher order elements. For Poisson equation
> > with p = 10, I can't use any more than 35x35 elements without having
> > a PETSc memory error.
> 
> p = 10 is pretty high... you can add a line

If I use p =3 on triangles, I can't use more than 120k elements - it requires
more than 1GB of memory. Without BLAS, assembly is no problem. Also, with the
p=10 example I was referring to triangles.

> 
>    blas.disp();
> 
> somewhere in your eval() function in the form generated by FFC and see
> how many entries you have in the matrix that gets shipped off to BLAS.
> 
> It sounds strange that you get a PETSc memory error. Degree 10 on
> tetrahedra has 286 degrees of freedom, so rougly 286*35*35 = 350350
> degrees of freedom total. That should be no problem for PETSc (if you
> have sufficient memory).
> 
> > Separate issue - with more complicated forms, I have trouble with anything
> > around p > 2 due to the memory requirements of ffc. Are there any simple
> > solutions to this?

With Poisson, I can go really high. I'll send the Cahn-Hilliard form shortly to
try out. With Cahn-Hilliard I'm quite limited.


> 
> I wasn't aware of this. With degree 10 Poisson, memory usage stays
> around 30MB. Can you give me an example (as simple as possible) that
> requires a lot of memory?
> 
> /Anders
>