[Tex/LaTex] List of symbols/abbreviations and macros

best practicesnomenclature

It's on my task list for a while now, and this post made me ask a follow up question which is, in my mind, a missing part when setting such a list.

As an example, think of the standard notation of an n-dim space; I would use the following code to typeset it: \mathbb{R}^n. Then, in order to make things quicker, I would define a macro \newcommand*{\Rn}{\mathbb{R}^n}. So far so good. Now, I want to have a list of symbols as well. In short, the question is: what is the best practice to generate a list of symbols for complicated symbols?

Let me consider the nomencl package, but I think the question is valid when one is using other alternatives as well. Currently, I have a file where I define all the macros I am using in my document, similar to the one I gave as an example above. Then, in order to generate a list's entry I would add 

\nomenclature{$\mathbb{R}^n$}{$n$-dimensonal real space}

where I use my macro \Rn for the first time. Is this the right/best way to go? One big drawback here is that when I would like to change the notation in the future, I will have to do it in two different places. Is there a smarter way to go? Somehow unify the two tasks of generating a list's entry and a macro which will be used in order to typeset the symbol later?

Best Answer

As long as you're sure that the first occurrence of \Rn is not in a section title or other moving argument, then you can define \Rn to emit the desired \nomenclature command and redefine itself:

\newcommand*{\Rn}{%
  \nomenclature{$\mathbb{R}^n$}{$n$-dimensional real space}%
  \gdef\Rn{\mathbb{R}^n}\mathbb{R}^n%
}

You can of course automatize this in a general macro:

\newcommand*{\definesymbol}[3]{%
   \def#1{\nomenclature{$#2$}{#3}\gdef#1{#2}#2}%
}

and then say

\definesymbol{\Rn}{\mathbb{R}^n}{$n$-dimensional real space}

and similarly for other symbols.

Caution: this will break miserably if you say \section{Definition of $\Rn$} and this is the first appearance of \Rn.

If you plan using those symbols in section titles, the following modified definition should work:

\makeatletter
\newcommand*{\definesymbol}[3]{\def#1{%
  \ifx\protect\@unexpandable@protect
    #2%
  \else
    \nomenclature{$#2$}{#3}\gdef#1{#2}#2%
  \fi}
}
\makeatother
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