1. School of Mathematics and Information Science, Key Laboratory of Mathematics and Interdisciplinary Sciences of Guangdong, Higher Education Institutes, Guangzhou University, Guangzhou, Guangdong 510006, China
2. Department of Applied Mathematics, Guangdong University of Finance, Guangzhou, Guangdong 510521, China
3. Department of Mathematical Sciences, University of Mazandaran, P.O. Box 47415-1468, Babolsar, Iran