Best composition of contractors

Dr. Gilles,
I have been trying to figure out which set of contractors is best for solving system with following characteristics and constraints:

x^2+y^2<=1;

 

I have been comparing defaultsolver with following:

1- CtcFwdBwd solver(sys.f);
RoundRobin bisec(prec);

CellStack buff;
Solver s(solver,bisec,buff);

2- CtcFwdBwd fb(sys.f);

CtcHC4 hc4(sys,prec);

CtcHC4 hc4_2(sys,prec,true);

CtcAcid acid(sys, hc4_2);

CtcCompo compo(hc4,fb,acid);

SmearSumRelative bisector(sys, prec);
CellStack buff;

Solver s(compo,bisector,buff);

Sometime 2- is better then the defaultsolver and 1- which is simple fwdbwd contractor and sometime for more complex case studies (which I cant share here), default or 1 is better then any composition. Is there any way of classification? or if there is any detailed information ? for what type of problem which contractor is best, so that it can be used to parallelize.
Regards,

Dear Usman,

There is no one-fits-all combination of contractors that works the best for all problems. However, we have proposed in the default solver a combination that seems to offer a good compromise in the majority of cases we have tested, please see:

http://www.ibex-lib.org/doc/tutorial.html#implementing-the-default-solver

Regards,

Gilles