1. Laboratory Mathematics , Djillali Liabes University of Sidi Bel Abbes , Algeria
2. Laboratory of Mathematics , University of Sidi Bel Abbes, Ecole Supérieure En Sciences Appliquées , B.P. 119, Tlemcen 13000 , Algeria
3. Laboratory of Stochastic Models, Statistic and Applications , Dr. Tahar Moulay University of Saida , Algeria