1. School of Mathematical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia. kgsmani1948@yahoo.com
2. Deanery of Business and Computer Sciences, Liverpool Hope University, Hope Park, Liverpool L16 9JD, UK
3. LITA, Universite Paul Verlaine-Metz, Ile du Saulcy, 57045 Metz Cedex, France