1. School of Mathematics and Econometrics, Hunan University, Changsha, Hunan, People’s Republic of China + Honghe University, College of Mathematics, Mengzi, Yunnan, People’s Republic of China
2. Hunan University, School of Mathematics and Econometrics, Changsha, Hunan, People’s Republic of China
3. Hunan Institute of Engineering, School of Science, Xiangtan, People’s Republic of China