[1] Shanghai Univ Elect Power, Coll Math & Phys, Shanghai 200090, Peoples R China
[2] King Abdulaziz Univ, Dept Math, Jeddah, Saudi Arabia
[3] Univ S Florida, Dept Math & Stat, Tampa, FL 33620 USA
[4] Zhejiang Normal Univ, Dept Math, Jinhua 321004, Zhejiang, Peoples R China
[5] Shandong Univ Sci & Technol, Coll Math & Syst Sci, Qingdao 266590, Shandong, Peoples R China
[6] North West Univ, Int Inst Symmetry Anal & Math Modelling, Dept Math Sci, Mafikeng Campus,Private Bag X2046, ZA-2735 Mmabatho, South Africa