Provide example for catching ConvergenceError

[andrenarchy]

We should add an example to the documentation for catching a ConvergenceError. A lot of people are unfamiliar with try/except so we can probably help them here a bit.

@zimoun What do you think?

[andrenarchy]

@zimoun: something like this should do the trick:

from krypy.utils import ConvergenceError
import warnings

# run a solver and catch ConvergenceErrors
def solve_unsafe(Solver, linear_system, **kwargs):
    try:
        return Solver(linear_system, **kwargs)
    except ConvergenceError as e:
        # warn the user (probably we should add more information to the message)
        warnings.warn('Solver did not converge.')
        # use solver of exception
        return e.solver

solver = solve_unsafe(Minres, linear_system, maxiter=5)

[zimoun]

yes, this kind of trick.
In my branch converr, I do that in the solver itself but it is not clean.

So, maybe, you could add this snippet of code in linsys.py or just in an example.

[andrenarchy]

+1 for example, that's the most visible way.