Institution: | 1. Department of Mathematics , Guangxi University , Nanning, Guangxi, 530004, P. R. China stx1963@163.com stxhql@gxu.edu.cn;3. Department of Mathematics , Guangxi University , Nanning, Guangxi, 530004, P. R. China;4. Department of Mathematics , Guangxi College of Finance and Economics , Nanning, Guangxi, 530003, P. R. China |