[1] Univ British Columbia, Dept Math, 1984 Math Rd, Vancouver, BC V6T 1Z2, Canada
[2] Hong Kong Polytech Univ, Dept Appl Math, Hong Kong, Hong Kong, Peoples R China
[3] South Univ Sci & Technol, Dept Math, Shenzhen 518055, Guangdong, Peoples R China
[4] Hong Kong Baptist Univ, Dept Math, Kowloon, Hong Kong, Peoples R China