1. Department of Mathematics, Shiraz University of Technology, Shiraz, Iran
2. Faculty of Mathematics and Statistics, Ton Duc Thang University, Ho Chi Minh City, Vietnam
3. Hunan Key Laboratory for Computation and Simulation in Science and Engineering, Key Laboratory of Intelligent Computing, Information Processing of Ministry of Education, School of Mathematics and Computational Science, Xiangtan University, Xiangtan, P. R. China