1. School of Mathematics and Statistics, The Center for Applied Mathematics of Guangxi, Guangxi Normal University, Guilin, Guangxi, P. R. China
2. School of Mathematics and Computing Science, Guilin University of Electronic Technology, Guilin, Guangxi, P.R. China
3. SUSTech International Center for Mathematics, Southern University of Science and Technology, Shenzhen, Guangdong, P.R. China