1. a Département de Mathématiques et de Génie Industriel , École Polytechnique de Montréal , C.P. 6079, succ. Centre-ville, Montréal, Québec H3C3A7, Canada
2. b Intelligent Systems Laboratory , 2139 Seamans Center, Department of Mechanical and Industrial Engineering, The University of Iowa , IA 52242-1527, USA