[petsc-users] Problems with preconditioners, which one?

[Filippo Spiga]

  Dear Jed, Hong, Barry and Matthew,
     first of all thank ou very much for you help. I really appreciate it!

I tired all your suggestions and now I'm able to solve my problem. Good 
news! The system reachs the convergence using 'superlu_dist', 'umfpack' 
and 'mumps'. However I experienced some problems using umfpack and 
mumps. In details:
- umpfpack: sometimes a values like '-1.3363470411775628e-16' or 
'1.1111231822598224e-15' appears instead of '0.0000000000000000e+00'
- mumps: for large system (~30k x 30k matrix) it seems to be stuck after 
a while. I used 8 processors. I cannot understand why this happens but 
I'm investigating...

SuperLU_DIST seems to work perfectly even if is slower that the other 
two. But I didn't do a exaustive performance comparison. Now my idea is 
do a lot of tests to measure the accuracy and the timing varying the 
dimension of the problem (I have different cubes to test), ksp_atol and 
ksp_rtol.  I'm able for all simple cube cases to costruct by myself the 
analitical solution so I will compare the computed one with the 
"analitical" one. That's perfect to tune the solver, isn't it?

Once again, thank you very much for your support.
Regards


Jed Brown ha scritto:
> You can use mumps and superlu_dist in parallel.  Or a domain
> decomposition method with direct subdomain solves, but then my earlier
> comment regarding being careful about the partition applies.

-- 

Filippo SPIGA

«Nobody will drive us out of Cantor's paradise.»
      -- David Hilbert