说明：  基于地球物理中的电法勘探原理，为了方便研究多层大地反演曲线，编写了本四层结构大地正演程序。本程序用C语言编写。
(Based on the the electrical prospecting geophysics principle, in order to facilitate the multi-layered earth inversion curve, the preparation of the four-layer structure of the earth forward the program. The program is written in C language.)