iswadi, Saib Suwilo, Tulus, Sawaluddin. “An Improved Search Direction Method for Solving Nonlinear Program Based on Generalized Reduced Gradient”. International Journal of Advanced Science and Technology, Vol. 29, no. 04, Apr. 2020, pp. 1980 -88, http://sersc.org/journals/index.php/IJAST/article/view/7962.