[Cbc] Several optimal integers solutions

[Nathann Cohen]

Hello everybody !

I first asked my question on list Osi, thinking it may be an
interface-related problem, but we found no answer and I hope you may be
knowledgeable on this point :-)

Here is my problem : I have been solving continuous and integer programs
with Cbc for some time now and it works absolutely fine !
Now, I would like to add some spices to what I am doing with it, by trying
to compute several integers solutions to linear programs.

For example, I would like the following program ( with x and y binary
variables ) :

Max:
   x + y
Constraints :
  x + y <= 1

to return the two solutions : x = 0, y=1 and x=1,y=0.

I saw there were functions in OsiClpInterface like setMaximumSolution and
getMaximumSolutions. I also found the function getSolutionCount in CbcModel
but it does not seem to do what I want it to do ;-)
I set the Maximum Number of Solutions to 200 and checked with
getMaximumSolutions there was no problem assigning the value, but when I
solve the previous problem getSolutionCount always return 1. Would you know
how to make it work properly  ? Would you have an example where several
solutions are found, which I could read to see both how it is done, and how
to iterate through all the solutions found after ? It it possible to set the
infinity as the MaximumNumber of solution if I want all of them ( I know
this can grow quite huge ! )

>From what I learnt on list Osi, it may well be that these functions act very
differently from what I first thought, and that the feature I am looking for
is not implemented yet. I am actually trying to enumerate *** all the
optimal solutions *** of a MIP containing binary/integer variables, and this
would just imply that the solver should nut cut branch whose objective is
"lesser or equal" to the current best integer solution, but only cut
branches whose objective is "strictly less" than the current best integer
solution.

I assure you I know several people who may be tremendously interested by
such a feature in CBC !! :-)

Thank you very much for your help !

Nathann Cohen
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