1. College of Mathematics and Information Science, Guangxi University, Nanning, China, 530004 (e-mail: wuhua_chen@163.com)
2. Math, Guangxi University, Nanning, China, 530000 (e-mail: deng_xiaoqing18@163.com)
3. School of Computer, Data and Mathematical Sciences, Western Sydney University, Sydney, NSW, Australia, 2751 (e-mail: w.zheng@westernsydney.edu.au)