1. Department of Mathematics, University of Hassan II, B.P 5366 Maarif, Casablanca, Morocco
2. Department of Mathematics, Chouaib Doukkali University, B.P 24.000 Route Ben Maachou, El Jadida, Morocco
3. MAEGE Laboratory, University of Hassan II, B.P 2634 Ain Sebaa,Casablanca, Morocco