Latex_commands_using_LuaTex

Creating Stable LaTeX Commands with Underscores and Dots using LuaTeX

1. Motivation

In LaTeX, the standard way to create LaTeX commands/macros is via \newcommand{}{}. For example:

\newcommand{\primalVar}{\mathbf{x}}

where the macro \primalVar creates a bold variable $\mathbf{x}$. To call this command, we simply write \primalVar.

However, the newly defined command \primalVar (using \newcommand{}{}) does not accommodate special characters like underscore _ and dot ., making the command hard to read, especially for lengthy commands. Taking inspiration from programming languages like Python, it would be preferable to utilize commands such as \primal.var or \primal_var.

In LaTeX, we can define such commands using \def keyword:

\def\primal.var{\mathbf{x}}

or

\def\primal_var{\mathbf{x}}

However, when using these commands in math mode, you may encounter errors or conflicts due to the altered meanings of . and _ in math mode.

To define such commands to be stable in math mode, we propose in this post a method using LuaTeX.

2. Solution approach using LuaTex

1. Create a variable LuaData in Lua code.

2. Create a set method (using Latex command) to add key "primal_var" and value "\\mathbf{x}" into LuaData.

3. Create a get method (using LaTeX command) to extract the value from the key.

The following is a minimal example demonstrating the suggested approach for creating such macros. To set and get macros, use the following syntaxes:

\setLuaData{primal_var}{\\mathbf{x}}
\getLuaData{primal_var}

In the following example code, please note that the desired output should resemble the following:
$$\min_{\mathbf{x} \in \mathbb R^n}\quad P(\mathbf{x})$$

\documentclass{article}

% Internal settings for LuaData
\usepackage{luacode}
\begin{luacode}
LuaData = {}
\end{luacode}
\newcommand{\setLuaData}[2]{\directlua{LuaData["#1"] = "#2"}}
\newcommand{\getLuaData}[1]{\directlua{tex.sprint(LuaData["#1"])}}

% LuaData defined by user
\usepackage{amsfonts}
\setLuaData{primal_var}{\\mathbf{x}}
\setLuaData{primal_func}{P}
\setLuaData{primal_space}{\\mathbb{R}^n}
\newcommand{\luda}[1]{\getLuaData{#1}} % optional

\begin{document}
$$\min_{\luda{primal_var} \in \luda{primal_space}} \quad 
\luda{primal_func}(\luda{primal_var})$$
\end{document}

Note. The provided code is sensitive to spaces. For instance, an error will occur if a space is present in the key, as in \getLuaData{primal_func }. To mitigate this issue, we need to remove spaces from the key. The following demonstrates how to remove spaces from the key, resulting in a command that is insensitive to spaces. Additionally, it throws an error when you try to get a key that is not defined.

\documentclass{article}

% Internal settings for LuaData
\usepackage{luacode}
\begin{luacode}
LuaData = {}
function setLuaData(key, value)
    local key = key:gsub("%s", "") -- remove spaces
    LuaData[key] = value
end
function getLuaData(key)
    local key = key:gsub("%s", "") -- remove spaces
    if LuaData[key] then
        tex.sprint(LuaData[key])
    else
        tex.sprint("LuaDataError")
    end
end
\end{luacode}
\newcommand{\setLuaData}[2]{\directlua{setLuaData("#1","#2")}}
\newcommand{\getLuaData}[1]{\directlua{getLuaData("#1")}}

% LuaData defined by user
\usepackage{amsfonts}
\setLuaData{primal_var}{\\mathbf{x}}
\setLuaData{primal_func}{P}
\setLuaData{primal_space}{\\mathbb{R}^n}
\newcommand{\luda}[1]{\getLuaData{#1}} % optional

\begin{document}
$$\min_{\luda{primal_var} \in \luda{primal_space}} \quad 
\luda{primal_func}(\luda{primal_var})$$
\end{document}

3. Conclusion

In this post, we suggested a method using LuaTeX to create stable LaTeX commands with underscores and dots, allowing for more versatile and readable macro names in LaTeX documents.