Laplacian

Laplacian[f, {x1, ..., xn}] gives the Laplacian ∂²f/∂x1² + ... + ∂²f/∂xn².

Examples

Laplacian of a function:

Laplacian[x^2 + y^2 + z^2, {x, y, z}]
(* 6 *)

2D Laplacian:

Laplacian[Sin[x] Cos[y], {x, y}]
(* -2 Cos[y] Sin[x] *)

Please visit the official Wolfram Language Reference for more details.