1. Politecnico di Milano, Department DEIB, via Ponzio 34/5, 20133 Milano, Italy
2. Royal Institute of Technology (KTH), Department of Automatic Control, Osquldas väg 10, Stockholm, Sweden
3. CNRS LAAS, Univ. de Toulouse, Equipe MAC, 7 Avenue du Colonel Roche, BP 54200 - 31031, Toulouse cedex 4, France