偏微分算符

贡献者： addis

预备知识　算符

　　例如

\begin{matrix} (1) & {(\frac{\partial}{\partial x} + 1)}^{2} = \frac{\partial^{2}}{\partial x^{2}} + 2 \frac{\partial}{\partial x} + 1, \end{matrix}

\begin{matrix} (2) & {(\frac{\partial}{\partial x} + \frac{\partial}{\partial y})}^{2} = \frac{\partial^{2}}{\partial x^{2}} + \frac{\partial^{2}}{\partial y^{2}} + 2 \frac{\partial^{2}}{\partial x \partial y} . \end{matrix}