Yes, that is the right definition: the values for x,y,z must be solutions of div(x,y,z).
There is a standard trick: introduce a new variable y' and reify that if y != 0, then y=y' and post div(x,y',z). The problem is that you do not get much propagation. Christian -- Christian Schulte, Professor of Computer Science, KTH, www.ict.kth.se/~cschulte/ -----Original Message----- From: users-boun...@gecode.org [mailto:users-boun...@gecode.org] On Behalf Of Max Ostrowski Sent: Tuesday, August 27, 2013 11:51 AM To: users@gecode.org Subject: [gecode-users] Division by zero I recognized that the div constraint for integers removes the zero from the domain of the second argument (to avoid division by zero). This seems to be a problem as i want to express the following: x/y+c > 7 reified b So, if b1 is true, y should not be zero or otherwise some undefined behaviour happens. So i add a constraint y != 0 reified b to avoid this case. (Sometimes it happens that this is done via other boolean variables, more complex constructs, own propagators etc..., but i always avoid the case that y is zero if b is true). To express this in gecode i currently use div(x,y,z); z + c > 7 refied b y != 0 reified b This gives wrong results, as in the case where b is false, y is also constraint to be != 0 via the div constraint. I thought about reifying the division with b, but this would also lead to wrong results. So any idea how to express this? Is removing the 0 from the domain via the div constraint really the right way? I could live with an undefined behaviour in the case that y \in {0}. Any ideas? Best Max Sample Code follows class TempSpace : public Space { public: TempSpace() : x_(*this,4), b_(*this,2) { x_[0] = IntVar(*this,1,3); x_[1] = IntVar(*this,-4,4); x_[2] = IntVar(*this, -10,10); x_[3] = IntVar(*this, -10,10); b_[0] = BoolVar(*this,0,1); b_[1] = BoolVar(*this,0,1); Gecode::div(*this,x_[0],x_[1],x_[2]); if (status()==SS_FAILED) std::cout << "failed " << std::endl; print(); IntArgs intArgs; IntVarArgs intVarArgs; intArgs << 1; intVarArgs << x_[2]; intArgs << 1; intVarArgs << x_[3]; linear(*this, intArgs, intVarArgs, IRT_EQ,0,b_[0],ICL_DEF); rel(*this,x_[2],IRT_NQ,0, b_[0], ICL_DEF); //rel(*this, b_[0], IRT_EQ, b_[1], ICL_DEF); if (status()==SS_FAILED) std::cout << "failed " << std::endl; print(); branch(*this, x_, branchVar, branchVal); } TempSpace(bool share, TempSpace& sp) : Space(share, sp) { x_.update(*this, share, sp.x_); b_.update(*this, share, sp.b_); } virtual TempSpace* copy(bool share) { return new TempSpace(share, *this); } void print() { std::cout << x_[0] << " " << x_[1] << " " << x_[2] << std::endl; } virtual ~TempSpace(){} void run() { dfsSearchEngine_ = new DFS<TempSpace>(this); while (enumerator_ = dfsSearchEngine_->next()) enumerator_->print(); } IntVarArray x_; BoolVarArray b_; DFS<TempSpace>* dfsSearchEngine_; TempSpace* enumerator_; }; _______________________________________________ Gecode users mailing list users@gecode.org https://www.gecode.org/mailman/listinfo/gecode-users _______________________________________________ Gecode users mailing list users@gecode.org https://www.gecode.org/mailman/listinfo/gecode-users
