1. Department of Mathematics, National University of Singapore, Singapore,
2. Faculty of Ocean Engineering Technology and Informatics, University Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia
3. Department of Mathematics, School of Science, University of Management & Technology, Lahore 54770, Pakistan
4. Department of Mathematics, Government Degree College (B), Sharqpur Shareef, Pakistan