Nopparat Pochai and  Rujira Deepana,  An Optimal Control of Water Pollution in a Stream Using a Finite Difference Method.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    August 2011, vol. 56(8). 1203 - 1205
    [viewed 24 January 2022]. Available from: https://publications.waset.org/pdf/6101.