Empheq: Flush Group Numbering To The Left
Let's dive into how you can tweak the empheq package to align group numbering to the left. This is a common desire when crafting documents with complex mathematical environments where you want better control over the layout. We'll break down the problem, look at the code snippet, and then explore a solution that ensures your equation numbers are flush left, enhancing readability and the overall aesthetics of your document.
Understanding the Issue
When using the empheq package, especially with grouped equations, the default numbering alignment might not always be what you desire. Specifically, you might find that the equation numbers are not perfectly aligned to the left margin, which can be visually distracting. Achieving a flush left alignment for these numbers can significantly improve the document's appearance, making it look cleaner and more professional.
The empheq package builds upon the amsmath package, providing an environment to create equation blocks that can be framed, have custom tags, and more. However, controlling the numbering alignment within these environments requires a bit of finesse. The goal is to modify the numbering behavior without disrupting the core functionality of empheq or introducing conflicts with other packages you might be using, such as mathtools or hyperref.
To tackle this, we need to understand how empheq handles equation numbering and how we can override its default behavior. This involves looking at the underlying mechanisms that control the placement of equation numbers and finding a way to hook into those mechanisms to enforce a left alignment. The solution should be robust enough to handle various scenarios, including different equation lengths and complexities, ensuring consistent alignment throughout your document. Ultimately, this customization will give you greater control over the final look and feel of your mathematical content, making it more polished and professional.
Initial Setup and Problematic Code
Before we implement the fix, let's establish the initial setup with the code that exhibits the issue. The LaTeX document starts with the usual preamble, loading necessary packages such as amsart for the document class, mathtools for enhanced math commands, hyperref for creating hyperlinks, and empheq for enhanced equation environments. Here’s the basic structure:
\documentclass[reqno]{amsart}
\usepackage{mathtools,hyperref}
\hypersetup{
colorlinks=true,
linkcolor=blue,
}
\usepackage[overload]{empheq}
\begin{document}
\begin{empheq}[left=\empheqlbrace]{align*}
a &= b + c \
d &= e + f
\end{empheq}
\begin{empheq}[box=\fbox\]{align*}
a &= b + c \
d &= e + f
\end{empheq}
\end{document}
In this setup, we're using the empheq environment in two different ways: first, with a brace on the left using left=\empheqlbrace, and second, with a box around the equations using box=\fbox. The align* environment is used to align the equations. The problem arises when the equation numbers are not flush left as desired.
The default behavior of empheq might result in the equation numbers being slightly offset or not perfectly aligned to the left margin, especially when used in conjunction with environments like align*. This can be visually unappealing and detract from the overall presentation of the document. The goal is to modify this behavior so that the equation numbers are consistently aligned to the left, regardless of the surrounding environment or the complexity of the equations.
To address this, we need to find a way to override the default numbering alignment within the empheq environment. This might involve adjusting the internal parameters that control the placement of equation numbers or using a combination of LaTeX commands and package options to achieve the desired effect. The solution should be flexible enough to work with different empheq configurations and should not introduce any unintended side effects or conflicts with other packages.
Solution: Implementing the Flush Left Alignment
To achieve the desired flush left alignment for equation numbers within the empheq environment, we can redefine the internal command that handles the equation numbering. Here’s how you can do it:
\documentclass[reqno]{amsart}
\usepackage{mathtools,hyperref}
\hypersetup{
colorlinks=true,
linkcolor=blue,
}
\usepackage[overload]{empheq}
\usepackage{etoolbox}
\makeatletter
\preto\empheq{\setcounter{equation}{\value{parentequation}}}
\patchcmd{\maketag@@@}{\hbox{\m@th\normalfont(\theequation\)}}{(\theequation)}{}{}
\makeatother
\begin{document}
\begin{empheq}[left=\empheqlbrace]{align*}
a &= b + c \
d &= e + f
\end{empheq}
\begin{empheq}[box=\fbox\]{align*}
a &= b + c \
d &= e + f
\end{empheq}
\end{document}
Let's break down this solution step by step. First, we include the etoolbox package, which provides tools for patching and modifying LaTeX commands. The key part of the solution is the \patchcmd command, which is used to modify the \maketag@@@ command. This command is responsible for creating the equation tag, which includes the equation number. Specifically, the \patchcmd command replaces the original equation number formatting \hbox{\m@th\normalfont(\theequation\)} with simply (\theequation). This change removes the \hbox, which was causing the equation number to be centered, and ensures that the number is flush left.
Additionally, \preto\empheq{\setcounter{equation}{\value{parentequation}}} is added to reset the equation counter at the start of each empheq environment to continue numbering from the parent equation.
By applying this patch, you ensure that the equation numbers are aligned to the left margin, providing a cleaner and more professional look to your document. This solution is robust and should work well with different configurations of the empheq environment, including those with braces, boxes, and other customizations.
Detailed Explanation
To fully grasp how this solution works, let's delve into the details of each component. The etoolbox package is a powerful tool for modifying LaTeX commands without having to redefine them entirely. The \patchcmd command allows you to replace specific parts of a command's definition, making it ideal for fine-tuning the behavior of existing environments and packages.
The \maketag@@@ command is an internal command used by amsmath and empheq to create the equation tag. By default, it wraps the equation number in an \hbox, which centers the number horizontally. This is why the equation number might not appear flush left.
The \patchcmd command takes four arguments:
- The command to be patched (
\maketag@@@). - The code to be replaced (
\hbox{\m@th\normalfont(\theequation\)}). - The replacement code (
(\theequation)). - Two placeholder arguments that are required but not used in this case.
By replacing the original code with simply (\theequation), we remove the \hbox and allow the equation number to be aligned to the left margin. The \m@th command ensures that the equation number is typeset in math mode, and \normalfont ensures that the default font is used.
Additionally, the line \preto\empheq{\setcounter{equation}{\value{parentequation}}} uses etoolbox to execute \setcounter{equation}{\value{parentequation}}} before each empheq environment. This ensures that the equation counter is correctly reset to continue numbering from the parent equation, maintaining the correct sequence of equation numbers throughout the document.
This solution is both effective and non-intrusive, as it only modifies the specific part of the code that controls the equation number alignment. It should work seamlessly with other packages and environments, providing a consistent and professional look to your mathematical documents.
Incorporating the Solution
Now that you understand the solution, let's talk about how to incorporate it into your LaTeX workflow. The best way to include this fix is to add the code snippet to your document's preamble, right after loading the empheq package. This ensures that the patch is applied before any empheq environments are used.
\documentclass[reqno]{amsart}
\usepackage{mathtools,hyperref}
\hypersetup{
colorlinks=true,
linkcolor=blue,
}
\usepackage[overload]{empheq}
\usepackage{etoolbox}
\makeatletter
\preto\empheq{\setcounter{equation}{\value{parentequation}}}
\patchcmd{\maketag@@@}{\hbox{\m@th\normalfont(\theequation\)}}{(\theequation)}{}{}
\makeatother
\begin{document}
... your document content here ...
\end{document}
By placing the code in the preamble, you ensure that the fix is applied globally to your document. This means that all empheq environments will have the flush left alignment for equation numbers, without you having to manually apply the fix to each environment.
If you're working on a large document with multiple files, you might want to consider creating a custom package or style file to store this fix. This allows you to easily reuse the fix in other documents without having to copy and paste the code every time. To create a custom package, simply save the code snippet in a .sty file and include it in your document using the \usepackage command.
For example, if you save the code snippet in a file named myempheqfix.sty, you can include it in your document like this:
\documentclass[reqno]{amsart}
\usepackage{mathtools,hyperref}
\hypersetup{
colorlinks=true,
linkcolor=blue,
}
\usepackage[overload]{empheq}
\usepackage{myempheqfix}
\begin{document}
... your document content here ...
\end{document}
This approach makes it easy to manage and reuse your custom fixes, ensuring consistency across all your documents.
Conclusion
In conclusion, achieving a flush left alignment for equation numbers within the empheq environment can significantly enhance the visual appeal of your documents. By using the etoolbox package and patching the \maketag@@@ command, you can easily override the default numbering behavior and ensure that your equation numbers are consistently aligned to the left margin.
This solution is robust, non-intrusive, and should work well with different configurations of the empheq environment. By incorporating this fix into your LaTeX workflow, you can create more professional and polished mathematical documents. Remember to add the code snippet to your document's preamble or create a custom package for easy reuse in other documents. Happy typesetting, guys!