1. School of Mathematics and Statistics, Gansu Key Laboratory of Applied Mathematics and Complex Systems, Lanzhou University, Lanzhou, China
2. Department of Mathematics and Statistics, International Islamic University, Islamabad, Pakistan
3. School of Environment and Ecology, Chongqing University, Chongqing, P.R. China
4. Department of Environmental Science, University of Veterinary and Animal Science, Lahore, Pakistan
5. Sustainable Development Study Center, Government College University Lahore, Lahore, Pakistan