Institution: | [1]Yangtze Center of Math., Sichuan University, Chengdu 610064 [2]College of Science, Chongqing Jiaotong University, Chongqing 400074 [3]College of Math. and Information Science, Leshan Normal University, Leshan 614004, Sichuan [4]College of Computer Science and Tech., Southwest University for Nationalities, Chengdu 610041 |