Soeryana Hasbullah, Endang, et al. “Mean-Variance Portfolio Optimization on Islamic Stocks by Using Non Constant Mean and Volatility Models and Genetic Algorithm”. International Journal of Engineering & Technology, vol. 7, no. 3.20, Sept. 2018, pp. 366-71, https://doi.org/10.14419/ijet.v7i3.20.19274.