What do you get with -snes_vi_monitor it could be it is taking a while to
get the right active set.
Barry
On Jan 16, 2012, at 6:20 PM, Ataollah Mesgarnejad 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
