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.
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}
\mathop{{}\bigtriangleup}\nolimits and \mathop{{}\Box}\nolimits which would ensure correct spacing in all situations. The {} is in order to avoid centering the operator with respect to the formula axis.
!\mathbin-part actually do ? And how would you make \bigtriangledown look like \nabla (in terms of vertical spacing) ?
Aug 6, 2017 at 17:09
\mathbin does nothing at all, because \mathbin\Box is eventually treated as an Ord atom. The “asymmetry” in the third example is due to the fact that the atoms are “Ord-Op-(Bin->Ord)-Ord”. The space is created by the first two atoms.
The operator is defined, in the international standard ISO 80000-1, as identified with the Unicode character U+2206 INCREMENT (mistakenly called DELTA in the standard), which has “Laplace operator” as one of its alias names. Thus, it is regarded as distinct from the Greek capital letter delta U+0394. This is however a logical, character-level distinction and does not imply that different glyphs must be used. On the other hand, many fonts make a distinction, sometimes very small, sometimes quite noticeable.
It seems to me that to make the difference in LaTeX, you would need to use a package that lets you enter a character by its Unicode number or enter Unicode characters as such. Along that second option, the following code seems to produce different renderings:
\documentclass{article}
\usepackage{unicode-math}
\setmathfont{XITS Math}
\begin{document}
U+2206: $∆$
U+0394: $Δ$
\end{document}
XITS Math which is the same as STIXGeneral, but doesn't raise warnings when used as a math font. The other change is for making clear what Unicode character produces each glyph.
\laplace" working with lualatex and \usepackage[math-style=ISO]{unicode-math}. Thanks!
\increment with unicode-math. If you want \laplace to use it, just do \newcommand{\laplace}{\increment}
unicode-math requires one of the compilers xelatex or Lualatex.
According to the Comprehensive LaTeX Symbol List one can use the symbol \Delta and corresponding \nabla to represent the Laplace operator.
I don't know if \Updelta is a possibility from txfonts/pxfonts.
There is another way to display the Laplacian. I found it in accident.
\mathcal{4}
So you can also define
\newcommand*\laplace{\mathop{}\!\mathcal{4}}
unicode-math (see above) \mathcal{4} will print 4
\Deltais used for it. See page 50.\Delta(apart from\mathcal{L}). :)\epsilonand\varepsilon.)