# [Trilinos-Users] Best direct solvers

John R. Cary cary at colorado.edu
Sat Oct 17 09:52:29 MDT 2009

```Hi Erik,

I guess that would mean a transpose to get all the data
for each tridiagonal solve on one processor?

Thanks.....John

Erik Boman wrote:
> Hi John,
>
> If I understand correctly, you have lots of tridiagonal systems
> corresponding to the x direction that can all be solved independently.
> In this case, I would suggest to remap your data (Epetra import/export)
> such that you can use a serial direct solver (KLU) on each tridiagonal
> system. You could perhaps view this as a domain decomposition approach
> and use Ifpack with Amesos/KLU as the subdomain solver.
>
> An alternative is to form one huge global (distributed) matrix and call
> Amesos with a 3rd party solver (SuperLU, MUMPS, etc.) but I think that
> would be less efficient.
>
> Erik
>
>
> On Fri, 2009-10-16 at 13:08 -0600, John R. Cary wrote:
>
>> Hi Eric,
>>
>> In this regard, suppose my matrix corresponded to differences in only one
>> direction (e.g., only x, not y, z).  On each line, I could do a direct
>> tridiagonal
>> solve if I were in serial.  What would be best for parallel in this case?
>>
>> Thanks...John
>>
>> Erik Boman wrote:
>>
>>> Jatin,
>>>
>>> Why do you need the inverse? If you wish to solve Ax=b, Trilinos has
>>> many solvers, both iterative (Ifpack, ML) and direct (Amesos).
>>>
>>> Regards, Erik
>>>
>>> On Fri, 2009-10-16 at 10:08 -0600, jatin ralhan wrote:
>>>
>>>
>>>> Hi,
>>>>
>>>> Does any one know whether it's possible to get the inverse of
>>>> Epetra_CrsMatrix (Matrix is Sparse Symmetric with filled diagonal
>>>> elements).
>>>>
>>>>
>>>> Jatin
>>>>
>>>>
>>>>
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>>>>
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>>
>
>
>

```