CoefficientAssignment属性

$$米\frac{{\partial }^{2}u}{\partial t^2}+d\frac{\partial u}{\partial t}-\nabla ·\left(c\nabla u\right)+\mathrm{一个}u=f$$

$$\begin{array}{l}-\nabla ·\left(c\nabla u\right)+\mathrm{一个}u=\lambda du\\ \text{或}\\ -\nabla ·\left(c\nabla u\right)+\mathrm{一个}u={\lambda }^2米u\end{array}$$