dolfin team mailing list archive

[Nuno David Lopes <ndl@xxxxxxxxxxxxxx>]

Is there any example,  sandbox or demo, showing how to use
SCOTCH with PETSc?

I would imagine that a 
/demo/fem/assembly  mixed with
/demo/function/projection 
would be a great help for beginners.

Thanks.    

On Wednesday 04 June 2008, Nuno David Lopes wrote:
> On Tuesday 03 June 2008, Anders Logg wrote:
> > On Tue, Jun 03, 2008 at 02:35:23PM +0100, Nuno David Lopes wrote:
> > > Thank you very much.
> > > This last e-mail made the subject more clear to me.
> > > In fact i was calling ./app
> > > I thougt PETSc should do all the parallel work from the inside of the
> > > ./app.
> > >
> > > Still with
> > > $mpirun -np 2 ./app
> > > (2-core PC)
> > > i get the same top results.: Cpu0=100% Cpu1=0%
> >
> > What app are you running? Are you running a simple sequential DOLFIN
> > program and expecting DOLFIN/PETSc to make it parallel?
>
> I was only expecting that when the KrylovSolver is called  inside the
> dolfin application then it went paralle?! Not on the rest of the code.
> The PETSc linear system solving algorithms aren't parallel?
> Isn't that the essential point of PETSc?
>
> As a I said before i really don't know much of parallel computation
> algorithms, but i was expecting some speed improvement if we
> use a parallel solver.
> (I'm  at the point that  assembly in parallel makes sense, parallel Linear
> System solving isn't clear form me).
>
> Ok I know that PETSc/hypre provides a good set of preconditioners and that
> is an advantage over the uBlas backend.
> But if we exclude the preconditioners, I  get PETSc::(gmres,ilu) slower
> than uBlas::(gmres,ilu).
> I didn't test other preconditioners yet....I've tried amg but on my 2Gb PC
> the memory wasn't enough...for the 566000x566000 system i'm testing.
>
> > At this point, parallel assembly is still experimental (but I hope we
> > can make it default for v0.9). There is a demo in
> >
> >  demo/fem/assembly/
> >
> > which does parallel assembly.
>
> And for this we need scotch right?
>
>
> By the way i've modified/simplified,
>  the VTKFile.cpp/h  and  created an RAWFile.cpp/h  for a raw format that is
> readable for instance in XD3D software.(it reads one file for mesh and
> other for the solution).
> I think its a good solution if we are working with one or few meshes, when
> compared  with the number of file solutions.
> It is much lighter than the standard vtk, xml formats, but also with less
> information, we only save the solutions.
> Is it of any interest?...i'm testing it.

-- 
Nuno David Lopes

e-mail:ndl@xxxxxxxxxxxxxx        (FCUL/CMAF)
           nlopes@xxxxxxxxxxxxxxx    (ISEL)
http://ptmat.ptmat.fc.ul.pt/%7Endl/ 

Thu Jun  5 16:39:46 WEST 2008