Laplace 算子¶ 可以记作是两个 Nabla 算子 点乘 \[ \Delta = \nabla^2 = \nabla \cdot \nabla = \frac{\partial^2}{\partial x^2} + \frac{\partial^2}{\partial y^2} + \frac{\partial^2}{\partial z^2} \] 可用 Laplace 算子对 梯度 求 散度 \[ \nabla \cdot (\nabla f) = \Delta f \]