当介质的导热系数是温度的函数时，热传导方程是非线性偏微分方程，作者采用基尔霍夫变换把它变成拉普拉斯方程，于是可以找到原问题的近似解析解。

The nonlinear equation of heat conduction is transformed into a Laplace's equation by applying the Kirchhoff transformation, and an analytic approximate solution of the equation is derived.

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基于基尔霍夫标量衍射理论，详细分析了输入、输出平面及变换函数抽样间距的选取原则。

Based on the Kirchhoff scalar diffraction theory, the principle to choose sampling periods in the input plane, output plane and transformation function was analyzed in detail.

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