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

[Mark Lohry]

On 5/16/2015 10:33 AM, Matthew Knepley wrote:
>
> 1) The best thing you can do for solver convergence is to start with a 
> well-scaled system. Is there a reason why
> you cannot non-dimensionalize your system?
>

Laziness/time, but yes I'll do this. Though this is a viscous flow 
solver, so any non-dimensionalization will still lead to values 
differing by 5+ orders of magnitude in certain areas.


>
> 3) If you have constraints on the variables, you might benefit from 
> using SNESVI
>
>


Perfect, thanks I wasn't aware of this. So SNESVIComputeVariableBounds 
can take a function that say, prevents negative densities/pressures?

> 2) Writing a custom line search is easier than messing with TR in my 
> experience
>

I'm interested to hear more about this. I haven't done much work with 
newton methods on this type of problem where overshoots lead to fatal 
errors.