[1] Univ Putra Malaysia, Dept Math & Stat, Fac Sci, Serdang 43400, Malaysia
[2] Univ Pertahanan Nas Malaysia, Ctr Def Fdn Studies, Dept Math, Kuala Lumpur 57000, Malaysia
[3] Univ Putra Malaysia, Inst Math Res, Serdang 43400, Malaysia
[4] Babes Bolyai Univ, Dept Math, Cluj Napoca 400084, Romania
[5] Acad Romanian Scientists, Bucharest 050044, Romania