Substituting character $l$ with $\ell$ throughout math mode

Question

How do I overwrite the default $l$ character so that it is substituted by $\ell$ throughout math mode? (More generally, is there an easy way to make such symbol substitutions?)

Answer 1

This is similar to how MinionPro deals with open vs closed mathematical g's.

\documentclass{article}
\mathcode`l="8000
\begingroup
\makeatletter
\lccode`\~=`\l
\DeclareMathSymbol{\lsb@l}{\mathalpha}{letters}{`l}
\lowercase{\gdef~{\ifnum\the\mathgroup=\m@ne \ell \else \lsb@l \fi}}%
\endgroup
\begin{document}
\( l = 2 \) \( \lim = 2 \)
\end{document}

Answer 2

There is if you are using Lyx or SWP. E.g., you can have SWP search for l in math (SWP is wysiwym) and replace it with \ell. It will do this and ignore l in text.

Answer 3

To do it via an external search-and-replace, you could use a script that I wrote called mathgrep. It's a perl script designed to do search and search-and-replace within maths sections of a LaTeX document.

The main limitation of this script is that it doesn't regard dollars as valid maths delimiters - but then, no-one uses them, right? Actually, I wrote a script to deal with that as well, which I called debuck for some reason that escapes me now.

(Oh yeah, I remember: dollar = buck.)

Answer 4

I think your best plan is to do a search and replace. You'll need to use some kind of regular expression (or, as user714 notes, so set up that can search selectively within math). The advantage of altering the source is you avoid any nasty side issues.