1. School of Mathematics and Statistics, Zhengzhou Normal University, Zhengzhou 450044, China
2. Electronic and Information Technology Department, Jiangmen Polytechnic, Jiangmen 529090, China
3. Department of Mathematics, University of Mazandaran, Babolsar 47416-95447, Iran
4. Department of Mathematical Sciences, University of South Africa, Pretoria 7945, South Africa
5. Department of Electrical Engineering, Institute of Engineering, Polytechnic of Porto, Rua Dr. Antonio Bernardino de Almeida 431, 4200-072 Porto, Portugal
6. Department of Mathematics and Mechanics, China University of Mining and Technology, Xuzhou Campus, Xuzhou, Jiangsu 221008, China