1. College of Information Science and Engineering, Ocean University of China, Qingdao 266100, China
2. College of Mathematics, Qingdao University, Qingdao 266071, China
3. School of Mathematical Sciences & College of Physical and Environmental Oceanography, Ocean University of China, Qingdao 266100, China
4. Institute of Information and Systems Engineering, Henan University of Economics and Law, Zhengzhou 450002, China