dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Mon, May 19, 2008 at 08:30:20AM -0500, Matthew Knepley wrote:
> On Mon, May 19, 2008 at 8:20 AM, Anders Logg <logg@xxxxxxxxx> wrote:
> > It looks to me like the storage needed is indeed n^2*num_cells. I'm
> > not fluent in Fortran, but that's how I interpret this line:
> >
> >  atw(idxatw(el,li,lj)) = atw(idxatw(el,li,lj)) + Atmp(li,lj)
> >
> > This looks expensive (in terms of memory), but maybe not that
> > expensive?
> 
> I think I should make the aggregation point again. The above line executes
> a function call for insertion of every value. This is a lot of
> overhead,

No, I think the above code would be very much faster than PETSc, but
use more memory. The way I interpret it, atw is an array and idxatw is
a *dense* rank 3 tensor so there's no searching, only lookup.

> not only
> for the call, but setting up loop bounds etc. That is why MatSetValues takes
> logical blocks, exactly what you get from FEM, I believe this could be the
> difference between our timing results.

No, the above code is not what we use in DOLFIN. We use MatSetValues
with blocks. The above code is femLego Fortran code.

-- 
Anders