[Tex/LaTex] Making math behaving like \mathit

Question

I often use descriptive names for predicates, terms and functions. However, due to the lack of kerning they don't look nice.

For example

$offer = surface \times force(now)$

renders as

Thus to avoid it use \mathit.

$\mathit{offer = surface \times force(now)}$

which renders as

which, arguably, looks better and it is easier to read.

To avoid to type \mathitm, I defined

\DeclareSymbolFont{italics}{\encodingdefault}{\rmdefault}{m}{it}

and

\DeclareMathSymbol{a}{\mathalpha}{italics}{`a}
...
\DeclareMathSymbol{z}{\mathalpha}{italics}{`z}
\DeclareMathSymbol{A}{\mathalpha}{italics}{`A}
...
\DeclareMathSymbol{z}{\mathalpha}{italics}{`Z}

Question(s)

Is this the "proper" way to do this?

What are the disadvantages/drawbacks of this approach? (I can use \mathnormal to go back to the standard behaviour, and I know that, for example, for the product of f and i I have to use f{}i to prevent the ligature).

Answer 1

It depends on several factors. If your math formulas are all built like that, then you might be justified in changing the mathcodes for the letters, although I recommend you not to do it.

Prefer a semantic markup: multiletter identifiers denote either variables or functions; define two commands, say \var and \func and type your formula as

\[
\var{offer}=\var{surface}\cdot\func{force}(\var{now})
\]

(don't use \times, please!). Now you have the freedom of choosing whatever representation for variables and functions you need, for instance

\newcommand{\var}[1]{\mathit{#1}}
\newcommand{\func}[1]{\mathit{#1}}

When your supervisor or a journal copy editor will tell you “Nice, but functions should be typeset in upright letters”, you'll answer “Wait a minute“, change the second line into

\newcommand{\func}[1]{\mathrm{#1}}

and recompile. Would it be the same with the change to the math codes?

Is it harder to type? I don't think so, particularly if you are an Emacs expert who's able to define a couple of shorthands.

---

Changing the math code of all letters is quite easy, as the code is repetitive. Don't forget to redeclare \mathit with \DeclareSymbolFontAlphabet in order not to waste a math family.

\DeclareSymbolFont{italics}{\encodingdefault}{\rmdefault}{m}{it}
\DeclareSymbolFontAlphabet{\mathit}{italics}

\makeatletter
\count@=`a \advance\count@\m@ne
\@whilenum{\count@<`z}\do{%
  \advance\count@\@ne
  \begingroup\lccode`A=\count@
  \lowercase{\endgroup
    \DeclareMathSymbol{A}{\mathalpha}{italics}{`A}%
  }%
}
\count@=`A \advance\count@\m@ne
\@whilenum{\count@<`Z}\do{%
  \advance\count@\@ne
  \begingroup\lccode`A=\count@
  \lowercase{\endgroup
    \DeclareMathSymbol{A}{\mathalpha}{italics}{`A}%
  }%
}
\makeatother

The loops can be simplified with expl3:

\usepackage{expl3}

\DeclareSymbolFont{italics}{\encodingdefault}{\rmdefault}{m}{it}
\DeclareSymbolFontAlphabet{\mathit}{italics}

\ExplSyntaxOn
\int_step_inline:nnnn { `A } { 1 } { `Z }
 {
  \group_begin:
  \char_set_lccode:nn { `A } { #1 }
  \char_set_lccode:nn { `B } { #1 + 32 }
  \tl_to_lowercase:n
   {
    \group_end:
    \DeclareMathSymbol{A}{\mathalpha}{italics}{`A}
    \DeclareMathSymbol{B}{\mathalpha}{italics}{`B}
   }
 }
\ExplSyntaxOff

The main problem, which requires using the \lowercase trick, is that it's the only way to generate a character token knowing its character code.

With a recent version of expl3 (released after 2015-09-09), one can avoid the \lowercase trick using \char_generate:nn.

\documentclass{article}
\usepackage{expl3}

\DeclareSymbolFont{italics}{\encodingdefault}{\rmdefault}{m}{it}
\DeclareSymbolFontAlphabet{\mathit}{italics}

\ExplSyntaxOn
\int_step_inline:nnnn { `A } { 1 } { `Z }
 {
  \exp_args:Nf \DeclareMathSymbol{\char_generate:nn{#1}{11}}{\mathalpha}{italics}{#1}
 }
\int_step_inline:nnnn { `a } { 1 } { `z }
 {
  \exp_args:Nf \DeclareMathSymbol{\char_generate:nn{#1}{11}}{\mathalpha}{italics}{#1}
 }
\ExplSyntaxOff

\begin{document}

\[
offer=surface\cdot force(now)
\]

\end{document}