[petsc-users] how to set the newton trust region size

[Mark Lohry]

I'm having an issue with SNES where the regular newton line search 
severely overshoots the solution update, ending up with irrecoverable 
values (negative densities and temperatures in a fluids code), so it 
seems newtonTR is a better way to go.

the manual says to set delta0 using -snes_tr_delta0, where the trust 
region radius is delta = delta0 * norm2( F ). My F values aren't well 
scaled and have pretty different values so norm2 of the whole thing 
isn't particularly meaningful. Ideally I'd like to tell SNES to limit 
the update to say, 10% of the current value of any given unknown. Is 
this possible?