Affiliation: | a School of Mathematics Science, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054, PR China b School of Computer Science and Technology, Southwest University for Nationalities, Chengdu, Sichuan 610041, PR China c School of Mathematics, Chengdu University of Information Technology, Chengdu, Sichuan 610225, PR China d School of Mathematics, Sichuan University, Chengdu, Sichuan 610064, PR China |