1. Depto. Ecuaciones Diferenciales y Análisis Numérico, Facultad de Matemáticas, Universidad de Sevilla, Sevilla, Spain
2. Faculty of Sciences of Sfax, Department of Mathematics, University of Sfax, Sfax, Tunisia
3. Department of statistics & OR, King Saud university, Riyadh Saudi Arabia
4. University of Sfax, Sfax, Tunisia