1. Department of MathematicsHarbin Institute of TechnologyHarbin150001People's Republic of China
2. School of Electrical Engineering, Tel Aviv UniversityTel Aviv69978Israel
3. Academy of Mathematics and Systems Science, Academia SinicaBeijing100190People's Republic of China
4. School of Computer Science and Applied Mathematics, University of the WitwatersrandWits2050JohannesburgSouth Africa