Affiliation: | 1. Department of Mathematics, Sun Yat-sen University, Guangzhou, Guangdong, People's Republic of Chinapingxiaozhai@163.com;3. Department of Mathematics, Sun Yat-sen University, Guangzhou, Guangdong, People's Republic of China;4. Faculty of Information Technology, Macau University of Science and Technology, Macau, People's Republic of China |