[gecode-users] Limits on nonlinear constraints

[Javier Romero]

Thanks for the fast answer. I tried decomposing the last constraint into
mul, sqr and linear rules, but i got the same result. I attached the code. I
compiled it by doing
g++ parallelepiped.cpp -lgecodeminimodel -lgecodeint -lgecodesearch
-lgecodegist -lgecodedriver -o parallelepiped
-- Javier Romero --


On Fri, Aug 20, 2010 at 2:58 PM, Guido Tack <tack at gecode.org> wrote:

> Javier Romero wrote:
>
> > Hi,
> > I'm a newbie in Gecode, but in the first stages of trying it i've found
> something that puzzles me. After writing a program with a set of highly
> nonlinear constraints which includes the following constraint (apart from
> others)
> >
> >     IntVar k = expr(*this, 2*x0*x1*x2);
> >     IntVar kc01= (*this,x2*(sqr(x0)+sqr(x1)-sqr(d01min)));
> >     IntVar kc02= (*this,x1*(sqr(x0)+sqr(x2)-sqr(d02min)));
> >     IntVar kc12= (*this,x0*(sqr(x2)+sqr(x1)-sqr(d12min)));
> >     rel(*this,k*(sqr(kc01)+sqr(kc02)+sqr(kc12)) <
> (k*k*k+2*kc01*kc02*kc12));
> >
> >  i get an output like this:
> [...]
> > That is, it returns inmediately with no solution. However, the problem
> has a solution, and actually it finds it by commenting the last lined of the
> code posted above (by chance; the constraint is actually necessary). This is
> how the output looks when the solution is found:
> [...]
> > I tested manually (and with a python script) that the solution obtained
> is compliant with the constraint that was removed. So i wonder if there is a
> limitation on the level of the nonlinearities in Gecode (i think it's
> unlikely), in the number of constraints (also unlikely) or what else could
> have happened. The code is basically an adaptation of SMM example to my
> arithmetic constraints. I can post it if necessary.
>
> If you could give me a small example that I can compile and run, I can have
> a look.  The code for posting non-linear expressions is relatively new, and
> there may be bugs that our test suite has not found.
>
> One thing you could try is to decompose the constraints (in particular the
> last line) manually, i.e. not use anything from minimodel.hh, but declare
> temporary IntVars and then only use the mult, linear, and sqr functions from
> int.hh.  If that works, then it's definitely a problem in how minimodel
> decomposes the constraint.
>
> Cheers,
>        Guido
>
> --
> Guido Tack, http://people.cs.kuleuven.be/~guido.tack/
>
>
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