1. Department of Operations Research and Information Engineering, Beijing University of Technology, Beijing 100124, P. R. China
2. Faculty of Management, University of New Brunswick, Fredericton E3B 5A3, Canada
3. School of Mathematics and Statistics Science, Ludong University, Yantai 264025, P. R. China
4. School of Mathematics and Statistics, Linyi University, Linyi 276005, P. R. China