1. Department of Mathematics, Faculty of Science, King Abdulaziz University, P.O. Box 80348, Jeddah 22254, Saudi Arabia
2. Department of Mathematics and Statistics, International Islamic University Islamabad, Islamabad 44000, Pakistan
3. KERMIT, Department of Mathematical Modeling, Statistics and Bioinformatics, Ghent University, Coupure Links 653, 9000 Ghent, Belgium