[petsc-users] SNESVI convergence spped

[Dmitry Karpeev]

What is the solution that you end up converging to, and what are the
boundary conditions?

Thanks.
Dmitry.

On Mon, Jan 16, 2012 at 6:20 PM, Ataollah Mesgarnejad <
amesga1 at tigers.lsu.edu> wrote:

> Dear all,
>
> I'm trying to use SNESVI to solve a quadratic problem with box
> constraints. My problem in FE context reads:
>
> (\int_{Omega} E phi_i phi_j + \alpha \epsilon dphi_i dphi_j dx) V_i -
> (\int_{Omega} \alpha \frac{phi_j}{\epsilon} dx) = 0 , 0<= V <= 1
>
> or:
>
> [A]{V}-{b}={0}
>
> here phi is the basis function, E and \alpha are positive constants, and
> \epsilon is a positive regularization parameter  in order of mesh
> resolution. In this problem we expect V  =1 a.e. and go to zero very fast
> at some places.
> I'm running this on a rather small problem (<500000 DOFS) on small number
> of processors (<72). I expected SNESVI to converge in couple of iterations
> (<10) since my A matrix doesn't change, however I'm experiencing a slow
> convergence (~50-70 iterations). I checked KSP solver for SNES and it
> converges with a few iterations.
>
> I would appreciate  any suggestions or observations to increase the
> convergence speed?
>
> Best,
> Ata
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