Logical markup for math symbols/variables, alternative to \newcommand

Question

I would like to use markup for any math symbols/variables (Sorry, I'm not sure what is the correct terminology here). The reason is to make late changes of the naming convention easier by just adjusting in one place. The following minimal example shows what I want to do and also the limitation of using \newcommand as it does not allow to use numbers in the macro name. If the commented line is compiled it will throw an error, however numbers are needed to describe some variables as there will be multiple ones just different by the number.

\documentclass{scrbook}
\begin{document}
\newcommand{\asteer}{a_{steer}}
\newcommand{\awheelfl}{a_{Wheel,FL}}
\newcommand{\awheelfr}{a_{Wheel,FR}}
%\newcommand{\rthrottle5}{r_{Throttle,q5}}
\begin{equation}
    a_{Steer} = a_{Wheel,FL} - a_{Wheel,FR}
\end{equation}
\begin{equation}
    \asteer = \awheelfl - \awheelfr
\end{equation}
\end{document}

I found a solution here: https://texfaq.org/FAQ-linmacnames (#2), however I am wondering if there is a better solution to that. Maybe \newcommand doesn't need to be used for this at all.

Cheers, Lukas

Answer 1

\documentclass{article}

\makeatletter
\newcommand\newname[1]{\expandafter\newcommand\csname #1\endcsname}

\newcommand\usename[1]{\@nameuse{#1}}
\makeatother

\begin{document}

\newname{a1}{this is a1}

\usename{a1}

% \newname{a1}{this is a1}% LaTeX Error: Command \a1 already defined.

\newname{a2}[3]{this is a2, it gets arguments #1, #2, #3}

\usename{a2}{aa}{bbb}{cccc}

\end{document}

---

I realize now this is quite close to #2 of posted link. But it is better because it allows the star-variant to be defined too, as weel as macros with optional arguments.

---

updated

\documentclass{article}

\makeatletter
\newcommand\newname[1]{\expandafter\newcommand\csname #1\endcsname}

\newcommand\usename[1]{\@nameuse{#1}}

\newcommand\ZZZ{}% check not defined
\def\ZZZ#1#{\@nameuse{ZZZ#1}}

\makeatother

\begin{document}

\newname{a1}{this is a1}

\usename{a1}

% \newname{a1}{this is a1}% LaTeX Error: Command \a1 already defined.

\newname{a2}[3]{this is a2, it gets arguments #1, #2, #3}

\usename{a2}{aa}{bbb}{cccc}

\newname{ZZZ1}{this is ZZZ1, it has no arguments, braces mandatory}
\newname{ZZZ2}{this is ZZZ2, it has no arguments, braces mandatory}
\newname{ZZZ---999}[2]{this is ZZZ-\mbox{}-\mbox{}-999 with arguments #1 and #2}


\ZZZ1{}

\ZZZ2{}

\ZZZ---999{aaaa}{bbbb}

\end{document}

Answer 2

I would use glossaries. This gives you the additional benefit to build list of symbols.

\documentclass{scrbook}
\usepackage{glossaries}
\newglossaryentry{asteer}
{%
  name={$a_{\mathrm{steer}}$},
  text={a_{\mathrm{steer}}},
  description={whatever},
  sort={a}
}

\newglossaryentry{awheelfl}
{%
  name={$a_{\mathrm{Wheel,FL}}$},
  text={a_{\mathrm{Wheel,FL}}},
  description={whatever},
  sort={a}
}
\begin{document}
\begin{equation}
    \gls{asteer} = \gls{awheelfl}
\end{equation}

\end{document}

Answer 3

In my answer to the question "Define a control sequence after that a space matters" I elaborated on a macro \name which is to be used as follows:

\name <tokens without braces>{<name of Control Sequence Token>}
→ <tokens without braces>\ControlSequenceToken

You can use the \name-macro both for defining and for calling macros.

---

Here comes the implementation:

\newcommand\name{}%
\long\def\name#1#{\romannumeral0\innername{#1}}%
%
\newcommand\innername[2]{%
  \expandafter\exchange\expandafter{\csname#2\endcsname}{ #1}%
}%
%
\newcommand\exchange[2]{#2#1}%

---

This is the way of using \name for defining macros:

Example 1:

\name\newcommand{rthrottle5} yields:
\newcommand\rthrottle5, thus you can, e.g., do:

\name\newcommand{rthrottle5}{r_{Throttle,q5}}
→ \newcommand\rthrottle5{r_{Throttle,q5}}

Example 2:

\name\global\long\def{foo} yields:
\global\long\def\foo, thus you can, e.g., do:

\name\global\long\def{foo}#1#2{foo's arg1: #1; foo's arg2: #2.} → \global\long\def\foo#1#2{foo's arg1: #1; foo's arg2: #2.}

---

Example 3:

This is the way of using \name for calling macros: Just leave the <tokens without braces>-argument empty:

\name{rthrottle5}
→ \rthrottle5

---

The <tokens without braces>-argument can also consist of a sequence of some more calls of the name-macro.

Example 4:

\name\name\let{foo}={bar}
→ \name\let\foo={bar}
→ \let\foo=\bar

Example 5:

\name\name\name\futurelet{foo}{bar}{baz}
→\name\name\futurelet\foo{bar}{baz}
→\name\futurelet\foo\bar{baz}
→\futurelet\foo\bar\baz

---

Using the \name-macro within your example:

\documentclass{scrbook}

\newcommand\name{}%
\long\def\name#1#{\romannumeral0\innername{#1}}%
\newcommand\innername[2]{%
  \expandafter\exchange\expandafter{\csname#2\endcsname}{ #1}%
}%
\newcommand\exchange[2]{#2#1}%

\begin{document}
\name\newcommand{asteer}{a_{Steer}}
\name\newcommand{awheelfl}{a_{Wheel,FL}}
\name\newcommand{awheelfr}{a_{Wheel,FR}}
\name\newcommand{rthrottle5}{r_{Throttle,q5}}
\begin{equation}
    a_{Steer} + r_{Throttle,q5} = a_{Wheel,FL} - a_{Wheel,FR} + r_{Throttle,q5}
\end{equation}
\begin{equation}
    \name{asteer} + \name{rthrottle5} = \name{awheelfl} - \name{awheelfr} + \name{rthrottle5}
\end{equation}

Or. if you like:

\begin{equation}
    \name\name\name\name\name%
    {asteer} + {rthrottle5} = {awheelfl} - {awheelfr} + {rthrottle5}
\end{equation}

\end{document}