1. Département de mathématiques, Université de Cergy-Pontoise, Site de Saint Martin, 2, avenue Adolphe Chauvin, 95302 Cergy-Pontoise, Cedex, France
2. Key Laboratory of Systems and Control, Academy of Mathematics and Systems Sciences, Academia Sinica, Beijing 100080, China
3. Departamento de Matemáticas, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain