understanding the output from -info

Lisandro Dalcin dalcinl at gmail.com
Thu Feb 8 10:50:17 CST 2007

On 2/8/07, Ben Tay <zonexo at gmail.com> wrote:
> i'm trying to solve my cfd code using PETSc in parallel. Besides the linear
> eqns for PETSc, other parts of the code has also been parallelized using
> MPI.

Finite elements or finite differences, or what?

> however i find that the parallel version of the code running on 4 processors
> is even slower than the sequential version.

Can you monitor the convergence and iteration count of momentum and
poisson steps?

> in order to find out why, i've used the -info option to print out the
> details. there are 2 linear equations being solved - momentum and poisson.
> the momentum one is twice the size of the poisson. it is shown below:

Can you use -log_summary command line option and send the output attached?

> i saw some statements stating "seq". am i running in sequential or parallel
> mode? have i preallocated too much space?

It seems you are running in parallel. The "Seq" are related to local,
internal objects. In PETSc, parallel matrices have inner sequential

> lastly, if Ax=b, A_sta and A_end from  MatGetOwnershipRange and b_sta and
> b_end from VecGetOwnershipRange should always be the same value, right?

I should. If not, you are likely going to get an runtime error.


Lisandro Dalcín
Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
PTLC - Güemes 3450, (3000) Santa Fe, Argentina
Tel/Fax: +54-(0)342-451.1594

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