1. School of Mathematics and Statistics, Center for Postdoctoral Studies of Management Science and Engineering, Shandong Normal University, Jinan 250014, People’s Republic of China.
2. School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ 85287-9709 USA.
3. Corresponding author. School of Mathematics/Shing-Tung Yau Center of Southeast University, Southeast University, Nanjing 210096, People’s Republic of China, and Nanjing Center for Applied Mathematics, Nanjing 211135, People’s Republic of China.