[1] North China Univ Water Resources & Elect Power, Sch Math & Stat, Zhengzhou, Peoples R China
[2] Yuncheng Univ, Sch Math & Informat Technol, Yuncheng, Peoples R China
[3] Shandong Univ, Zhongtai Secur Inst Financial Studies, Jinan, Peoples R China
[4] Shandong Natl Ctr Appl Math, Shandong Prov Key Lab Financial Risk, Jinan, Shandong, Peoples R China