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[Murtazo Nazarov <question108259@xxxxxxxxxxxxxxxxxxxxx>]

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

Murtazo Nazarov posted a new comment:
Anders Logg wrote:
> Question #108259 on DOLFIN changed:
> https://answers.launchpad.net/dolfin/+question/108259
>
> Anders Logg posted a new comment:
> On Thu, Apr 29, 2010 at 04:14:21PM -0000, Murtazo Nazarov wrote:
>   
>> Question #108259 on DOLFIN changed:
>> https://answers.launchpad.net/dolfin/+question/108259
>>
>>     Status: Answered => Solved
>>
>> Murtazo Nazarov confirmed that the question is solved:
>> Yes, it seems hypre in my solver does not converge only in the first
>> iteration. Before it was just a warning, but with the latest dolfin it
>> stoped since it is assumed that it is an error.
>>
>> Here I made a test for the same problem using the following lines:
>>
>>    solver = KrylovSolver("gmres")
>>    solver.parameters["monitor_convergence"] = True
>>    solver.parameters["error_on_nonconvergence"] = False
>> ..
>>
>> "Old" dolfin gives:
>> ....
>> Applying boundary conditions to linear system.
>> Applying boundary conditions to linear system.
>> Solving linear system of size 4184 x 4184 (PETSc Krylov solver).
>>   0 KSP preconditioned resid norm 2.663347782311e+02 true resid norm 1.371810197831e+01 ||Ae||/||Ax|| 7.817835153984e+08
>> *** Warning: Krylov solver did not converge (PETSc reason -4).
>> PETSc Krylov solver (gmres, hypre) failed to converge in 0 iterations.
>> ...
>>
>> and the latest dolfin gives:
>>
>> Applying boundary conditions to linear system.
>> Applying boundary conditions to linear system.
>> Solving linear system of size 4184 x 4184 (PETSc Krylov solver).
>>   0 KSP preconditioned resid norm 6.346755394553e+02 true resid norm 3.269022479529e+01 ||Ae||/||Ax|| 3.675021072956e+08
>> *** Warning: Krylov solver did not converge (PETSc reason -4).
>> PETSc Krylov solver (gmres, hypre) failed to converge in 0 iterations.
>>
>> It happened because of the luck of stabilization in startup.
>>
>> It is nice to know about the latest flags in the parameter list for the
>> Krylov solver.
>>
>> murtazo
>>     
>
> ok, good to know. So there is nothing wrong with the solver.
>
> I suggest you let "error_on_nonconvergence" stay true, otherwise you
> will not see when it fails.
>
> --
> Anders
>
>   

yes, you are right. I put it false only for the first time-step, then I 
change it to be true. Otherwise I still get warning, which I usually track.

murtazo

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