1. College of Mathematics and Statistics, Nanjing University of Information Science and Technology, Nanjing 210044, P. R. China
2. Jiangsu International Joint Laboratory on System Modeling and Data Analysis, Center for Applied Mathematics of Jiangsu Province, Nanjing University of Information Science and Technology, Nanjing 210044, P. R. China
3. Jiangsu Vocational College of Electronics and Information, Huaian 223003, P. R. China
4. College of Continuing Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P. R. China