Sirodj, Dwi Agustin Nuriani, and Ivan Gunawan. “Recycling Solid Waste of Coconut Oil Industry: A Response Surface-Goal Programming Approach”. Jurnal Optimasi Sistem Industri, vol. 19, no. 2, Nov. 2020, pp. 111–121, http://josi.ft.unand.ac.id/index.php/josi/article/view/146.