Laplacian

${\nabla }^2=\nabla \cdot \nabla$ is the Divergence $\nabla \cdot$ of the Del or Nabla $\nabla$. In three dimensional space, we have ${\nabla }^2=\frac{{\delta }^2}{\delta x^2}+\frac{{\delta }^2}{\delta y^2}+\frac{{\delta }^2}{\delta z^2}$