1. Guangdong Province Key Laboratory of Computational Science, Sun Yat-sen University, Guangzhou, Guangdong Province 510275, People's Republic of China
2. School of Mathematics, Sun Yat-sen University, Guangzhou, Guangdong Province 510275, People's Republic of China
3. School of Financial Mathematics and Statistics, Guangdong University of Finance, Guangzhou 510521, People's Republic of China