1. School of Mathematics and Statistics, Xidian University, Xi’an, Shanxi, 710071, People’s Republic of China.
2. Corresponding author. School of Mathematics and Statistics, HNP-LAMA, Central South University, Changsha, Hunan, 410083, People’s Republic of China.
3. School of Mathematics and Statistics, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada.