[1] Lanzhou Univ, Gansu Key Lab Appl Math & Complex Syst, Sch Math & Stat, Lanzhou 730000, Gansu, Peoples R China
[2] Hong Kong Polytech Univ, Dept Appl Math, Hung Hom, Kowloon, Hong Kong, Peoples R China
[3] Nanjing Univ, Dept Math, Nanjing 210093, Jiangsu, Peoples R China
[4] Univ South Carolina, Dept Math, Columbia, SC 29208 USA