College of Mathematics and Information Science Northwest Normal University;
Lanzhou 730070;
China Institute of Applied Mathematics;
Lanzhou Jiaotong University;
Lanzhou 730070;
China;
Department of Mathematics ZheJiang Normal University;
Jinhua 321004;
China;
School of Information and Electrical Engineering Lanzhou Jiaotong University;
Lanzhou 730070;
China;
College of Mathematics and Information Science Northwest Normal University;
Lanzhou 730070;
China;