[Tex/LaTex] Subscript equivalent of ‘ for \prime

best practicesmath-mode

I am working through the TeXbook and I came across the section (pg. 130) where ' and \prime are discussed. Knuth mentions that TeX treats \prime as a large symbol that appears only in superscripts instead of making it a smaller symbol that has already been shifted up into the superscript position. Part of the reason is because some authors actually use \prime in the subscript position.

I know $y'_1+y''_2$ yields a typographical output equivalent to that of $y^\prime_1+y^{\prime\prime}_2$ , but I am wondering if there is an equivalent to ' for putting the \prime into the subscript position.

For example, $h'$ is typographically equivalent to $h^\prime$ , but is $h_\prime$ equivalent to any "quicker" expression (i.e., involving an apostrophe or something similar)? I tried $h_'$ , but this produces an error; then I tried $h_{'}$ , but I realized this is equivalent to typing $h_{{}^\prime}$ .

Basically, is there a character X where $hX$ and $h_\prime$ are equivalent?

Best Answer

Just mimic what the kernel does for \prime:

\documentclass{article}

\makeatletter
\def\active@math@sprime{_\bgroup\sprim@s}
{\catcode`\`=\active \global\let`\active@math@sprime}
\def\sprim@s{%
  \prime\futurelet\@let@token\spr@m@s}
\def\spr@m@s{%
  \ifx`\@let@token
    \expandafter\spr@@@s
  \else
    \ifx_\@let@token
      \expandafter\expandafter\expandafter\spr@@@t
    \else
      \egroup
    \fi
  \fi}
\def\spr@@@s#1{\sprim@s}
\def\spr@@@t#1#2{#2\egroup}
\mathcode`\`="8000
\makeatother

\begin{document}

Normal use: `test'.

Math: $h`$ and $h``$ and also $h`_{1}$.

\end{document}

enter image description here

What does this do? First of all, a backquote in math mode is dealt with as if it were an active character, because of \mathcode`\`="8000; TeX will look for a definition of ` as active character, which is \active@math@sprime.

When it's found first in a possible sequence of backquotes, TeX expands \active@math@sprime, so doing _\bgroup\sprim@s. This starts a subscript, exploiting the fact that _\bgroup<tokens>\egroup is legal syntax. Now \sprim@s is expanded, which typesets \prime and does

\futurelet\@let@token\spr@m@s

This looks at the following token, stores it into \@let@token without removing it from the input stream and executes \spr@m@s.

This macro does some tests:

if \@let@token is a backquote, the \else...\fi part is removed by \expandafter and \spr@@@s is executed;
if \@let@token is _ the \else...\fi\fi part is removed by the triple \expandafter and \spr@@@t is executed;
none of the above: \egroup is executed which will close the subscript.

Now let's look at \spr@m@s: it is defined just to remove the next token (which is a backquote) and does \sprim@s again. This is how $h``$ becomes $h_\bgroup\prime\prime\egroup$ .

The macro \spr@@@t has two arguments: the first is _ which is simply gobbled and the second is the intended subscript, which is closed by \egroup that balances the initial \bgroup. This is how $h`_{1}$ becomes $h_\bgroup\prime 1\egroup.

Snippet managers

A flexible and powerful way of working with templates is to use a snippet manager. In Replace the `$$ ... $$` macro with the `\[ ... \]` macros? - Prefer the way LaTeX lays it out, but `$` are faster to write you find a simple explanation of how a snippet manager works. What you do is simply to store each template as a separate snippet and use the power of the snippet manager to modify it on expansion.

YASnippet

Here is an example with YASnippet, a snippet manager for Emacs. The following steps are how to create a simple article template:

Enter the mode you want the snippets in. In this case I guess it is LaTeX-mode.
Do M-x yas/new-snippet.
Enter a name for the snippet.
You will now get a chance to edit the snippet. Mark everything by doing C-x h, then kill it by C-w.

You will now have an empty snippet. Paste the following into it and make sure the snippet ends after \end{document} and not on a new line:

# -*- mode: snippet -*-
# name: article
# key: arttemp
# --
\documentclass{article}

\usepackage[${1:english}]{babel}

\title{${2:Title}}
\author{${3:Author}}

\begin{document}

\maketitle

$0

\end{document}

Do C-c C-c to save and load the snippet.

Now you can use the snippet in LaTeX-mode by writing arttemp and then pressing Tab. Note how $1, $2, $3 and $0 defines tab stops and that the three first has default values which can be overridden. Here is an animation that shows how the snippet works:

Animation of the snippet above

Obviously the snippet in the example is a very simple snippet. One snippet I use as a template for articles is 172 lines long. It contains \usepackages for the packages I commonly use, package configuration and macro definitions for macros I commonly use. For more information on how to write snippets see the documentation.

With YASnippet your snippets are stored as files. The manual describes how you can organize snippets. I keep my snippets in ~/.emacs.d/mysnippets and load them by the following in my .emacs:

(setq yas/root-directory "~/.emacs.d/mysnippets"); Develop and keep personal snippets under ~/emacs.d/mysnippets
(yas/load-directory yas/root-directory); Load the snippets

By syncing ~/.emacs.d/mysnippets between computers I get the same snippets on all of them.

[Tex/LaTex] How to create a new extensible symbol

Scott Pakin's Comprehensive LaTeX Symbol List identifies the structure of extensible delimiters in section 8.2 Resizing symbols (p 100-102):

All variable-sized delimiters are defined (by the corresponding .tfm file) in terms of up to five segments, as illustrated by Figure 1 on page 102. The top, middle, and bottom segments are of a fixed size. The top-middle and middle-bottom segments (which are constrained to be the same character) are repeated as many times as necessary to achieve the desired height.

This is merely informative since I am unfamiliar with the procedure of how to create these things in a .tfm file.

Conveniently, scalerel provides \scaleleftright[<max width>]{<left obj>}{<stuff>}{<right obj>} (and a comparable \stretchleftright) for scaling/stretching both <left obj> and <right obj> to the height of <stuff> (constrained, if required and optional, to a width of <max width>). Here's a quick example:

enter image description here

\documentclass{article}
\usepackage{scalerel}% http://ctan.org/pkg/scalerel
\begin{document}
\[ \stretchleftright{\dagger}{\displaystyle\sum_{i=1}^n i}{\dagger} \]
\[ \scaleleftright{\dagger}{\displaystyle\sum_{i=1}^n i}{\dagger} \]
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Working with templates

Snippet managers

YASnippet

[Tex/LaTex] How to create a new extensible symbol

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