[petsc-users] DMComposite and ksp

[gouarin]

Thanks for the reply.

My Dirichlet condition was wrong for the multi domain. I fixed it and 
now I have the same iteration number for my KSP.

I'm very sorry.

Loic


On 03/03/2011 15:19, Barry Smith wrote:
> On Mar 3, 2011, at 6:52 AM, gouarin wrote:
>
>> Hi,
>>
>> I'm still working on my stokes problem with 2 DM (one for the velocities and an other for the pressure). I do the best preallocation for my matrix.
>> After the construction of my matrix, I do a matrix vector operation and I compare the result for one process and 2 processes. If I pay attention to the numbering of my fields between these 2 problems, I have the same result.
>>
>> But when I do just 2 iterations of my ksp solver, I don't have the same result at the end and of course the residual is not the same.
>    What preconditioner are you using? Unless you use Jacobi you will always get a different set of iterations. (And even with Jacobi due to different order of operations you will eventually see a different convergence route between 1 and 2 processes.  You cannot be concerned about this, the things to be concerned about are:
>
> 1) Do 1 and 2 processes eventually converge to the same answer (bad news if they do not)
>
> 2) Does 2 process converge almost as quickly to the answer as one process (bad news if adding more processes slows the convergence greatly so the solution time ends up being longer).
>
>    Barry
>
>
>
>> Do you know what I do wrong ?
>>
>> Thanks,
>> Loic
>>
>> -- 
>> Loic Gouarin
>> Laboratoire de Mathématiques
>> Université Paris-Sud
>> Bâtiment 425
>> 91405 Orsay Cedex
>> France
>> Tel: (+33) 1 69 15 60 14
>> Fax: (+33) 1 69 15 67 18
>>


-- 
Loic Gouarin
Laboratoire de Mathématiques
Université Paris-Sud
Bâtiment 425
91405 Orsay Cedex
France
Tel: (+33) 1 69 15 60 14
Fax: (+33) 1 69 15 67 18