说明：  二维稳态导热问题。设材料物性均为常数，均质无内热源。已知它的左边界是温度为T2的等温边界，其他三个边界均为温度为T1的等温边界。导热区域为边长L的正方形。
(two-dimensional steady-state heat conduction problems. Based material properties are constant, no heterogeneity within the heat source. It is known to have a threefold T2 is the temperature of the isothermal boundary, the other three border are temperature T1 isothermal boundary. Regional conduction length L of the square.)