1. University of Tunis El Manar, National Engineering School of Tunis, Laboratory of Engineering Mathematics EPT, BP 743, La Marsa 2078, Tunisia
2. Ibn Zohr University, Polydisciplinary Faculty of Ouarzazate, BP 638, Ouarzazate, Morocco
3. LMAH, University of Le Havre, 25 rue Ph. Lebon, BP 540, 76058 Le Havre Cedex, France
4. Laboratory of Engineering Mathematics, Polytechnic School, BP 743, La Marsa 2078, Tunisia