Theoretically the numerical solution of Poisson's equation or Laplace's equation plus Neumann boundary condition calculated by the boundary integration method is not unique.

使用边界积分方法求解已知第二类边界条件的拉普拉斯方程或泊松方程时，理论上解是不唯一的。

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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.

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。

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