1. Departamento Ecuaciones Diferenciales y Análisis Numérico, Facultad de Matemáticas Universidad de Sevilla Sevilla Spain
2. Department of Mathematics Faculty of Sciences of Sfax Sfax Tunisia
3. Department of Mathematics Alkurmah University College, Taif University Taif Saudi Arabia
4. Faculty of Sciences of Tunis, Department of Mathematics University of Tunis El Manar Tunis Tunisia