[Couenne] Obscure error message when running Couenne

[Daniel T. Fokum]

Hello Pietro,

Thanks for your help.

Daniel

> Hello Daniel,
>
> the "Error in AMPL evaluation" errors are usually encountered during
> calls to the NLP solver (Ipopt), which uses the AMPL interface to
> compute the values of the functions. Couenne uses an NLP solver to
> find feasible solutions, among other methods. When the halt_or_error
> option is set, this will simply terminate Ipopt, not Couenne, and
> therefore Ipopt will not return a solution. However, a solution is
> found by the branch-and-bound as shown in the output you sent:
>
>> Cbc0004I Integer solution of 6749.23 found after 2226 iterations and 53
>> nodes (88.23 seconds)
>
> (probably a solution to the LP relaxation that is also MINLP
> feasible). The lower bounding procedure and the procedure that checks
> for feasibility of a solution do not use Ipopt. Therefore, if Couenne
> terminates as in your case, the solution found is optimal regardless
> of these errors.
>
> Hope this helps.
>
> Cheers,
> Pietro