1 Department of Basic Courses, Nanjing Institute of Technology, Nanjing 211167, China 2 Faculty of Science, Jiangsu University, Zhenjiang, Jiangsu 212013, China 3Department of Mathematical Sciences, International Institute for Symmetry Analysis and Mathematical Modelling, North-West University, Mafikeng Campus, Private Bag X 2046, Mmabatho 2735, South Africa 4Department of Mathematics, University of Caldas, Manizales 275, Colombia 5 Department of Mathematics, University of Central Florida, Orlando, FL 32816-1364, USA