1. Department of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000, Pakistan;
2. Department of Electrical and Computer Engineering, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah 21589, Saudi Arabia
3. Department of Mathematics, University of Wah, Quaid Avanue, The Mall, Wah Cantt 47040, Pakistan
4. Department of Mathematics, College of Science, Majmaah University, P.O. Box 1712, Az Zulfi 11932, Saudi Arabia e-mail: