1. Department of Statistics, Nanjing Audit University, Nanjing 211815, P.R. China
2. School of Economics and Management, Southeast University, Nanjing 210096, P.R. China
3. Faculty of Mathematics and Informatics, Vilnius University, Naugarduko 24, Vilnius LT 03225, Lithuania
4. Institute of Mathematics and Informatics, Vilnius University, Akademijos 4, Vilnius LT 08663, Lithuania