SHAO Yingchao1, DU Zhaobin2, YANG Jilin3, QIN Keyun1
1.School of Mathematics, Southwest Jiaotong University, Chengdu 610031, China
2.Zhengzhou Technical College, Zhengzhou 450121, China
3. College of Fundamental Education, Sichuan Normal University, Chengdu 610068, China