1. School of Mathematical Sciences, University of Electronic Science and Technology of China, Sichuan, Chengdu 610054, China
2. Department of Applied Mathematics, Southwest Petroleum University, Chengdu 610500, China
3. State Key Laboratory of Oil and Gas Reservoir and Exploitation, Chengdu 610500, China
4. Department of Mathematics, Sichuan University, Sichuan, Chengdu 610064, China