Affiliation: | [1]College of Mathematics and Computer Science, Hebei University, Baoding 071002, China Hebei Provincial Center of Mathematics, Shijiazhuang 050016, China [2]College of Mathematics and Computer Science, Hebei University, Baoding 071002, China [3]Department of Mathematics, Chengde Teachers College for Nationalities, Chengde 067000, China [4]Faculty of Science, Huzhou Teachers College, Huzhou 313000, China |