dolfin team mailing list archive

[Nuno David Lopes <ndl@xxxxxxxxxxxxxx>]

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