If fit goes wrong convergence test can report positively although fit didn't converge

[jkfindeisen]

If for some reason the first step is too large (too large lambda?), the parameters are way off after the first iteration and then never recover, but still chi_square-previous_chi_square will be zero sometimes and the convergence test will be positive although the model and the parameters are far from anything good.

Not sure yet, what exactly is wrong there and how to fix it but it surely deserves to be looked at.

This may also happen in other fit frameworks, but maybe not to the same extent. The value of the initial lambda parameter as well as a more complex analysis of the converged state may improve the situation

[superchromix]

@jkfindeisen Please post an example code which reproduces the problem.