1. School of science, Northwest A&F University, Yangling, Shannxi, People's Republic of China
2. Key Laboratory of High Performance Computing and Stochastic Information Processing (HPCSIP) (Ministry of Education of China), College of Mathematics and Statistics, Hunan Normal University, Changsha, Hunan, People's Republic of China
3. Department of Mathematical Sciences, Georgia Southern University, Statesboro, GA, USA