[1] Xiangnan Univ, Coll Math & Informat Sci, Chenzhou 423000, Peoples R China
[2] Appl Sci Univ, Coll Comp Sci, POB 5055, Manama, Bahrain
[3] Sun Yat Sen Univ, Dept Math, Guangzhou 510275, Peoples R China
[4] COMSATS Univ Islamabad, Dept Math, Abbottabad 22060, Khyber Pakhtunk, Pakistan