Muhafzan
Department of Mathematics, Faculty of Mathematics and Natural Science, Andalas University, Kampus UNAND Limau Manis, Padang, Indonesia
Malik Hj. Abu-Hassan
Department of Mathematics, Faculty of Science, University Putra Malaysia, Serdang, Malaysia
Leong Wah June
Department of Mathematics, Faculty of Science, University Putra Malaysia, Serdang, 43400 Malaysia