Si f:Ω→R{\displaystyle f:\Omega \to \mathbb {R} } a l'é na fonsion C2{\displaystyle C^{2}} definìa ansima a n'ansem duvert Ω⊆Rn{\displaystyle \Omega \subseteq \mathbb {R} ^{n}}, as ciama laplacian d'f{\displaystyle f} la fonsion Δf=∑i=1n∂2f∂xi2{\displaystyle \Delta f=\sum _{i=1}^{n}{\frac {\partial ^{2}f}{\partial x_{i}^{2}}}}. La notassion Δ{\displaystyle \Delta } a ven da Gabriel Lamé.