[1] Xian Jiaotong Univ Shaanxi, Sch Econ & Finance, Appl Econ, Xian, Shaanxi, Peoples R China
[2] Dept Agr Gilgit Baltistan, Baltistan, Pakistan
[3] Xian Jiaotong Univ Shaanxi, Sch Econ & Finance, Xian, Shaanxi, Peoples R China
[4] Univ Salerno, Dept Math, Salerno, Italy