1. Department of Mathematics, Quaid-I-Azam University, Islamabad 44000, Pakistan;
2. Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia
3. Department of Mathematics, Quaid-I-Azam University, Islamabad 44000, Pakistan
4. Department of Mathematics, University of Wah, Wah Cantt 47040, Pakistan e-mail: