[1] Renmin Univ China, Dept Math, Beijing 100872, Peoples R China
[2] Chinese Acad Sci, Inst Computat Math & Sci Engn Comp, Acad Math & Syst Sci, Beijing 100080, Peoples R China
[3] Nanjing Normal Univ, Sch Math & Comp Sci, Nanjing 210097, Peoples R China
[4] Karlsruhe Inst Technol, Inst Appl & Numer Math, D-76128 Karlsruhe, Germany