[Tex/LaTex] Correct symbol for the Laplace operator ($\Delta$)

Question

What is the correct symbol to use for the Laplace operator? It looks almost like the big Delta $\Delta$, but it should look different so that it is not confused with the Delta.

Currently, I use $\vec \nabla^2$, which is unambiguous, but not pretty.

Answer 1

If you use the D'Alembert operator as well, you might find pretty using the symbol \bigtriangleup for your Laplace operator, in order to get a similar look as the \Box symbol that is being used for D'Alambertian. In the following, a tricky construction with \mathop and \mathbin is used to get the proper spacing:

\documentclass{article}

\usepackage{amsmath,amssymb}

\newcommand*\Laplace{\mathop{}\!\mathbin\bigtriangleup}
\newcommand*\DAlambert{\mathop{}\!\mathbin\Box}

\pagestyle{empty}

\begin{document}

\begin{gather*}
  \phi(1+\Laplace A) \neq \phi(1+\Delta A)
\\ 
  \phi(1+\DAlambert A) \neq \phi(1+\Laplace A)
\\ 
  f\Laplace g
\end{gather*}

\end{document}