1. Lecturer, Research Centre for Modeling and Simulation, National Univ. of Sciences and Technology, Islamabad 44000, Pakistan.
2. Assistant Professor, School of Natural Sciences, National Univ. of Sciences and Technology, Islamabad 44000, Pakistan; formerly, Research Centre for Modeling and Simulation, National Univ. of Sciences and Technology, Islamabad 44000, Pakistan (corresponding author).
3. Professor, Dept. of Mathematics, Quaid-I-Azam University 45320, Islamabad 44000, Pakistan; and Dept. of Mathematics, Faculty of Science, King Abdulaziz Univ., P.O. Box 80257, Jeddah 21589, Saudi Arabia.
4. Professor, Dept. of Mathematics, Faculty of Science, King Abdulaziz Univ., P.O. Box 80257, Jeddah 21589, Saudi Arabia.