1. Fujian Province University Key Laboratory of Computational Science, School of Mathematical Sciences, Huaqiao University, Quanzhou 362021, People’s Republic of China.
2. School of Mathematics and Statistics, Northwestern Polytechnical University, Xi’an 710129, People’s Republic of China, and School of Mathematics and Center for Nonlinear Studies, Northwest University, Xi’an 710127, People’s Republic of China.
3. Corresponding author. Center for Applied Mathematics of Guangxi, Guangxi Normal University, Guilin, Guangxi 541004, People’s Republic of China.