[Getdp] Non-linear Wiki review

[janvrot at infolink.com.br]

Hello

Some time ago I contributed to the Wiki with the non-linear magnetostatic example, gathering
information from Christophe Geuzaine, Johan Gyselinck and others.

Now I'm back to getdp and I restarted reviewing that Wiki example.

I noticed that the non-linear case with the Newton scheme for the vector potential converges to
reasonable results in few iterations, while for the scalar potential the converge was bad, specially
for high magnetization levels, where the BH curve is most non-linear, giving in one of the cases bad
results, even with a 1e-6 error convergence.

So I wonder if I  messed up the received suggestions in the preparation of the presented examples.
Could someone kindly check them? Johan? Christophe?

Thanks
Janvrot