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[Kent <question108259@xxxxxxxxxxxxxxxxxxxxx>]

Question #108259 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/108259

Kent proposed the following answer:

with assemble_system you might use cg, if the variational
form is symmetric. For mass matrix with bc I've used
CG + Jacobi prec.

Kent


> Question #108259 on DOLFIN changed:
> https://answers.launchpad.net/dolfin/+question/108259
>
> N.A. Borggren proposed the following answer:
> Hello,
>    It seems that my Krylov solver was working better a few weeks ago than
> now as well.  I applied the assemble_system suggestion above but I still
> get
> an error message for a humble 756x756 matrix that works just fine without
> the 'gmres' option in solve.  I was relying on 'gmres' before to solve
> problems when just "solve(A, self.u1.vector(), b)" (PETSc LU solver,
> umfpack) would run out of memory.  So I've returned to the conundrum of
> how
> to solve larger systems when neither of these options work.  Any
> suggestions? I'm running on Fedora 12 and had quite an adventure (still
> unsuccesful on my home computer) making dorsal with the Fedora 11 platform
> run.  Is it something wrong with my build?
>    Thanks,
>        Nathan Borggren
>
>
> Assembling linear system and applying boundary conditions...
> Matrix of size 756 x 756 has 9910 nonzero entries.
> Solving linear system of size 756 x 756 (Krylov solver).
> Traceback (most recent call last):
>   File "Lorenz.py", line 120, in <module>
>     z.Run()
>   File "/home/nborggren/Codes/Aleph/Dynamics/DynSys.py", line 166, in Run
>     solve(A, self.u1.vector(), b,'gmres')
>   File
> "/home/nborggren/Work/FEniCS/build/lib/python2.6/site-packages/dolfin/cpp.py",
> line 3834, in solve
>     return _cpp.solve(*args)
> RuntimeError: *** Error: Krylov solver did not converge.
>
>
> On Mon, Apr 26, 2010 at 1:06 PM, Kent
> <question108259@xxxxxxxxxxxxxxxxxxxxx>wrote:
>
>> Question #108259 on DOLFIN changed:
>> https://answers.launchpad.net/dolfin/+question/108259
>>
>>    Status: Open => Answered
>>
>> Kent proposed the following answer:
>> > Anders Logg wrote:
>> >> Question #108259 on DOLFIN changed:
>> >> https://answers.launchpad.net/dolfin/+question/108259
>> >>
>> >>     Status: Open => Answered
>> >>
>> >> Anders Logg proposed the following answer:
>> >> On Sat, Apr 24, 2010 at 03:38:42AM -0000, Murtazo Nazarov wrote:
>> >>
>> >>> New question #108259 on DOLFIN:
>> >>> https://answers.launchpad.net/dolfin/+question/108259
>> >>>
>> >>> Hi,
>> >>>
>> >>> My solver was working until I recompiled dolfin for some reasons.
>> The
>> >>> Petcs Krylov solver does not converges:
>> >>>
>> >>> Solving linear system of size 4184 x 4184 (PETSc Krylov solver).
>> >>> terminate called after throwing an instance of 'std::runtime_error'
>> >>>   what():  *** Error: PETSc Krylov solver did not converge (PETSc
>> >>> reason -4).
>> >>>
>> >>> However it works well with LUSolver.
>> >>>
>> >>> Does anyone had similar problem?
>> >>>
>> >>
>> >> Are you sure it used to converge? We recently changed a warning to an
>> >> error, so it might be that your old solver didn't converge but you
>> >> only thought it did.
>> >>
>> >>
>> >
>> > I checked now the output of my old solver. It converged with hypre.
>> But,
>> > now it converges with LUSolver but not with Krylov solver.
>> >
>> > I simple solve the mass matrix, after applying Dirichlet boundary
>> > conditions.
>> >
>> > murtazo
>> >
>>
>> I've also seen this a number of times. The problem goes away when
>> using assemble_system that makes the matrix symmetric.
>>
>> I don't have a good explaination, though. And I think it is a bit
>> strange.
>>
>> Kent
>>
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