dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

On Wednesday 19 August 2009 19:11:42 Garth N. Wells wrote:
> Johan Hake wrote:
> > On Wednesday 19 August 2009 18:50:13 Garth N. Wells wrote:
> >> Johan Hake wrote:
> >>> On Wednesday 19 August 2009 17:29:52 Garth N. Wells wrote:
> >>>> What's going on behind the scene when I copy one vector to another in
> >>>> PyDOLFIN using
> >>>>
> >>>>      u0.vector()[:] = u.vector()[:]
> >>>
> >>> When I add:
> >>>
> >>> u2 = Function(V)
> >>> u2.vector()[:] = u.vector()[:]
> >>>
> >>> # Plot solution
> >>> plot(u2)
> >>>
> >>> In a the Poisson demo it works fine.
> >>
> >> In parallel?
> >
> > Yupp!
> >
> >>> This type of slice only uses the assignment operator.
> >>
> >> The GenericVector assignment operator?
> >
> > Yes. This is done in __setslice__/__getslice__ in the extended python
> > class.
>
> I don't see then why the we end up inside
>
>    _compare_vector_with_vector
>
> for the Cahn-Hilliard demo when running in parallel?

Are you sure it is in 

  _compare_vector_with_vector

this should only kick in if you used '==' or some other comparison operator. 

When I run this demo in parallel, I get passed the assignment line but it 
stops when calling the solve function with the following message:

Traceback (most recent call last):
  File "demo.py", line 86, in <module>
    Traceback (most recent call last):
solver.solve(problem, u.vector())
RuntimeError: *** Error: MUMPS is required for parallel symbolic LU.
 

> >> I delved into the problem and the program ends up in the function
> >> _compare_vector_with_vector from dolfin_la_get_set_items.i. It uses
> >> GenericVector::get and GenericVector::set. These need to be used with
> >> caution in parallel.
> >
> > Yes, when other type of slices are used we need to find a way to do that
> > in parallel. I have just started digging in the parallel code, and need
> > to look into all the changes to get familiar with it before I try to
> > solve this.
>
> This shouldn't be too hard.
>
>     set(const double* block, uint m, const uint* rows)
>
> works in parallel but
>
>     get(double* block, uint m, const uint* rows)
>
> doesn't yet (not too hard to fix though). The really evil functions are
>
>    set(const double*)
>
> and
>
>    get(double*)

I think I am only using

   set(const double* block, uint m, const uint* rows)
   get(double* block, uint m, const uint* rows)

However GenericVector.array is using the get(double*) function, and returns 
some fishy numbers in the numpy.array.

Johan

> Garth
>
> > The best solution would be to have a full fledge VectotView in place ;)
> >
> > Johan
> >
> >> Garth
> >>
> >> Other slices might not
> >>
> >>> work. Have not checked.
> >>>
> >>> Johan
> >>>
> >>>> ? The issue is that it doesn't work in parallel.
> >>>>
> >>>> Garth
> >>>> _______________________________________________
> >>>> DOLFIN-dev mailing list
> >>>> DOLFIN-dev@xxxxxxxxxx
> >>>> http://www.fenics.org/mailman/listinfo/dolfin-dev