1. LAMA Laboratory, Faculty of Sciences Dhar El Mahraz, Sidi Mohamed Ben Abdellah University, Fez, Morocco
2. Africa Business School, Mohammed VI Polytechnic University, Lot 660, Hay Moulay Rachid, Ben Guerir 43150, Morocco
3. Mathematics Department, Faculty of Sciences Semlalia, Cadi Ayyad University, Boulevard Prince Moulay Abdellah, P.O. Box 2390, Marrakesh 40000, Morocco