[petsc-users] advice on different performance using hypre:euclid through petsc vs directly through hypre

[Matt Funk]

Just reread my email and i need to apologize for all the grammatical errors
in it. Hopefully it still makes sense.

matt

On Sat, Nov 12, 2011 at 11:34 PM, Matt Funk <matze999 at gmail.com> wrote:

> Hi,
> i am solving a system for which is interfaced both with petsc and hypre.
> I.e. i have some data and build the matrix up either via petsc or hypre
> (for hypre i use the sstruct interface). The output of the system after
> several hundred timestep is only different on the order of 1e-04 for a
> non-linear system. So in terms of accuracy things agree pretty well such
> that i think i can rule out that the issue is related to the matrix itself.
>
>  Anyway, for both interfaces i am using the Euclid/BiCGSTAB combination
> (rel.tol. 1e-08). I would expect similar results in terms of performance
> which i do not get.
> For PETSC:HYPRE_EUCLID:BICGSTAB for the first 10 timesteps i get 12
> iterations per timestep. Using HYPRE directly i get convergence after 3
> iterations. At first the it seems like the tolerance is the issue. I get
> the residuals and iterations as follows:
> 1) HYPRE:
> HYPRE_SStructBiCGSTABGetNumIterations(m_SStruct->ssSolver, &a_iterations);
> HYPRE_SStructBiCGSTABGetFinalRelativeResidualNorm(m_SStruct->ssSolver,
> &a_relres);
> 2) PETSC:
> m_ierr = KSPGetIterationNumber(m_ksp, &a_iterations_solver);
> m_ierr = KSPGetResidualNorm(m_ksp, &a_relres_solver);
> Other than that i do change the type of norm or anything.
>
> The residual using HYPRE is on the order of 1e-09
> The residual using PETSC is on the order of 1e-04
>
> So not only dies HYPRE use less iterations, it also gives the smaller
> residual.
>
> I think this is a user error as i cannot really explain why there would be
> such a vast difference. I was just wondering if anyone has any insight as
> to what else i could try or an attempt at some explanation as to what i am
> seeing.
>
> thanks
> matt
>



-- 
Matt Funk
Research Associate
Plant and Environmental Scienc. Dept.
New Mexico State University
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