NOTE : this article is a work in progress and not finished yet.
The Laplacian operator
$\Delta u$ is the divergence of the gradient, that is the sum of the second-order partial derivatives
$\nabla^2 u$ of a multivariate function, which represents the local curvature of this function. This operator is widely used for edge-detection[^1], as well as in partial-differential equations (Poisson, etc.), and other [...]