1. College of Mathematics, Taiyuan University of Technology, 030024, TaiYuan, Shanxi, ChinaCollege of Mathematics, Taiyuan University of Technology, 030024, TaiYuan, Shanxi, China
2. College of Mathematics, Taiyuan University of Technology, 030024, TaiYuan, Shanxi, China
3. Human Sciences Research Council (HSRC), South Africa
4. Tshwane university of Technology, South Africa