[Ipopt] Understanding Ipopt errors

[Clara Meunier]

Hi,

I have some trouble with understanding issues for my Ipopt optimization.
Indeed, I use it for a project during my internship, and optimization in general is something new for me.

I do an analysis step by step, and at each time, I need to do an optimization. 
However, for many steps, I have errors like "Optimizer failed: Ipopt: Restoration failed (status -2)" with "Restoration phase is called at point that is almost feasible, with constraint violation 7.417025e-016. Abort." or "Optimizer failed: Ipopt: Maximum iterations exceeded (status -1)".
I would like to know if the results obtained at the end of the step with error are useable or totally wrong ?

Moreover, I don't really understand what the restoration phase does, so I don't know which parameters I need to work on to solve these errors. If someone is able to explain it with simple words, it would be nice of him/her.

Any suggestion is welcome !

Best regards,

Clara