Tea Poklepović and  Zdravka Aljinović and  Mario Matković,  Efficient Frontier - Comparing Different Volatility Estimators.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    March 2015, vol. 100(4). 214 - 221
    [viewed 27 February 2020]. Available from: https://publications.waset.org/pdf/10001020.