1. UR Analyse Non-Linéaire et Géometrie, UR13ES32, Department of Mathematics, Faculty of Sciences of Tunis, University of Tunis El-Manar, 2092 El Manar II, Tunisia. E-mails: ahmed.bchatnia@fst.utm.tn, sabrine.chebbi@fst.utm.tn
2. Institute for Scientific Computing and Applied Mathematics, Indiana University, 831 E. 3rd St., Rawles Hall, Bloomington IN 47405, United States. E-mail: mahamoud@indiana.edu
3. Department of Mathematics, College of Sciences, University of Sharjah, P.O.Box 27272, Sharjah, UAE. E-mail: asoufyane@sharjah.ac.ae