1. Department of Mathematics, Faculty of Sciences and Techniques (M’Ghila), P. O. Box 523, Béni Mellal, Morocco
2. Department of Mathematics, Faculty of Sciences and Techniques, Abdelmalek Essaâdi University, P. O. Box 416, Tangier, Morocco
3. Department of Mathematics, Faculty of Sciences, Ibn Tofail University, P. O. Box 133, Kénitra, Morocco
4. Department of Network and Telecommunications Engineering, LISERT, National School of Applied Sciences (ENSA), Sultan Moulay Slimane University, P. O. Box 77, Khouribga, Morocco