1. Department of Applied Mathematics, University of Science and Technology Beijing, Beijing 100083, China
2. Department of Mathematics, Zhejiang Normal University, Jinhua 321004, Zhejiang, China
3. Department of Mathematics, King Abdulaziz University, Jeddah, Saudi Arabia
4. School of Mathematics, South China University of Technology, Guangzhou 510640, China
5. Department of Mathematics and Statistics, University of South Florida, Tampa, FL 33620, USA
6. International Institute for Symmetry Analysis and Mathematical Modelling, Department of Mathematical Sciences, North-West University, Mafikeng Campus, Private Bag X 2046, Mmabatho 2735, South Africa
7. Department of Mathematics, Beijing University of Chemical Technology, Beijing 100029, China