1. Key Laboratory of Intelligent Computing and Information Processing of Ministry of Education, School of Mathematics and Computational Science, Xiangtan University, Xiangtan, Hunan 411105, P. R. China
2. School of Mathematics and Computational Science, Xiangtan University, Xiangtan, Hunan 411105, P. R. China
3. Xingjian College of Science and Liberal Arts, Guangxi University, Nanning, Guangxi 530004, P. R. China