1. Department of Mathematics, Quaid-I-Azam University, Islamabad 45320, Pakistan;
2. Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, P.O. Box 80257, Jeddah 21589, Saudi Arabia
3. Department of Mathematics, Quaid-I-Azam University, Islamabad 45320, Pakistan e-mail: