1. School of Mathematics and Information Science, Guangxi University, 530004, P.R.C. dqjin@foxmail.com
2. School of Mathematics and Information Science, Guangxi University, 530004, P.R.C. dain_qin@163.com
3. School of Mathematics and Information Science, Guangxi University, 530004, P.R.C. mryang_0021@163.com
4. School of Mathematics and Information Science, Guangxi University, 530004, P.R.C. 499417726@qq.com