[Couenne] Unknown operator error

[Pietro Belotti]

Hi Łukasz,

I get the same issue you reported, but I'm afraid it isn't fixable:
Couenne exits after finding an operator, ifnl(), that is implemented
by AMPL but not by Couenne. It is the operator that takes three inputs
(a,b,c), and outputs b if a is true and c otherwise. If you were able
to re-formulate your problem without the AMPL if operator I think
Couenne might be able to solve it.

As for factorable functions, they are functions that can be generated
by using a finite set of operators {+,-,/,*,^,log,exp,sin,cos,tan} and
by variables and constants. This includes any expression such as
x1+sin(x2)+5 log(x1^4 - x3*x6 - 4^(x1+3)) but not, for instance,
black-box functions. Your problem appears to be factorable indeed,
though that one operator makes it unsolvable in Couenne.

I'm CCing the mailing list as somebody else might be interested.

Regards,
Pietro

On Wed, Jun 24, 2015 at 12:38 PM, Łukasz Segiet <lukas.segiet at gmail.com> wrote:
> Dear Pietro,
>
> I have attached the file to this email.
>
> I have a question: what exactly do you mean by factorable functions?
>
> Regards,
> Łukasz
>
> On 22 June 2015 at 13:36, Pietro Belotti <petr.7b6 at gmail.com> wrote:
>>
>> Dear Łucasz,
>>
>> from the output the problem file seems to contain an AMPL operator
>> that is not recognized by Couenne. Do you use a defined function? In
>> that case, since Couenne requires all functions to be factorable
>> (unlike Ipopt and Bonmin), the problem cannot be solved by Couenne. If
>> not, it would be interesting to check that file if you can post it.
>>
>> Regards,
>> Pietro
>>
>> On Mon, Jun 22, 2015 at 12:13 PM, Łukasz Segiet <lukas.segiet at gmail.com>
>> wrote:
>> > Dear All,
>> >
>> > I am trying to run Couenne on some .nl files and ipopt has no problems
>> > with
>> > them, but Couenne does. This is the output I get.
>> >
>> > bash-4.1$ ./couenne problem.nl
>> > Couenne 0.4.8 --  an Open-Source solver for Mixed Integer Nonlinear
>> > Optimization
>> > Mailing list: couenne at list.coin-or.org
>> > Instructions: http://www.coin-or.org/Couenne
>> >
>> > ERROR: unknown operator (address 0p7f25acb37830), aborting.
>> >
>> > Does anyone know what can be the issue and if there are some limitations
>> > on
>> > what Couenne can solve (and what is already solvable by ipopt)?
>> >
>> > Sincerely yours,
>> >
>> > Lukasz Segiet
>> >
>> >
>> > _______________________________________________
>> > Couenne mailing list
>> > Couenne at list.coin-or.org
>> > http://list.coin-or.org/mailman/listinfo/couenne
>
>