Irawan, D., H. Grandis, and P. Sumintadiredja. “Quasi-2D Resistivity Model from Inversion of Vertical Electrical Sounding (VES) Data Using Guided Random Search Algorithm”. Journal of Mathematical and Fundamental Sciences, vol. 47, no. 3, Dec. 2015, pp. 269-80, doi:10.5614/j.math.fund.sci.2015.47.3.5.