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[Kent <question108259@xxxxxxxxxxxxxxxxxxxxx>]

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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