Take the 2-minute tour ×
TeX - LaTeX Stack Exchange is a question and answer site for users of TeX, LaTeX, ConTeXt, and related typesetting systems. It's 100% free, no registration required.

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.

share|improve this question
6  
According to the Comprehensive LaTeX Symbol List \Delta is used for it. See page 50. –  azetina Oct 13 '12 at 18:07
1  
Also, the only symbol used on Wikipedia - the source of all knowledge - is \Delta (apart from \mathcal{L}). :) –  Werner Oct 13 '12 at 18:16
    
Link to Comprehensive LaTeX Symbol List. See page 50. –  azetina Oct 13 '12 at 18:17
    
don't you mean page 150, @azetina? Page 50 has only arrows. –  c.p. Oct 13 '12 at 18:22
1  
Even if they look different, they will be confused. Don't use them with different meanings! (The same applies, e.g., to \epsilon and \varepsilon.) –  Hendrik Vogt Oct 13 '12 at 19:23
show 4 more comments

3 Answers 3

up vote 8 down vote accepted

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}

Example

share|improve this answer
2  
I'd use \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. –  egreg Oct 13 '12 at 21:15
    
The d'Alambert operator will come eventually since I am a physicist. I like your solution, since it looks consistent. –  queueoverflow Oct 14 '12 at 14:29
add comment

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}

enter image description here

share|improve this answer
1  
I've taken the liberty of modifying your example; first to use 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. –  egreg Oct 13 '12 at 21:19
    
@egreg: Could you please add a possibility to define a command for the "U+2206". I would like to get a "\laplace" working with lualatex and \usepackage[math-style=ISO]{unicode-math}. Thanks! –  LaRiFaRi Sep 2 '13 at 15:31
1  
@LaRiFaRi The symbol is called \increment with unicode-math. If you want \laplace to use it, just do \newcommand{\laplace}{\increment} –  egreg Sep 2 '13 at 15:40
    
It seems that unfortunately the package unicode-math requires one of the compilers xelatex or Lualatex. –  strpeter Oct 30 '13 at 14:58
add comment

According to the Comprehensive LaTeX Symbol List one can use the symbol \Delta and corresponding \nabla to represent the Laplace operator.

enter image description here

I don't know if \Updelta is a possibility from txfonts/pxfonts.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.