How to Change Reference Number in LaTeX 

LaTeX is renowned among researchers, engineers, and academics for its precision in formatting documents, particularly those that are heavy on mathematical notation and references. However, as robust as LaTeX is, certain tasks—such as changing or customizing reference numbers—can be less than intuitive for beginners and even intermediate users.

TLDR:

Modifying reference numbers in LaTeX can be done in a few different ways, depending on whether you’re using automatic citation packages like BibTeX or BibLaTeX, or manual bibliography entries. Users can either manipulate bibliography entries directly, redefine numbering styles, or use label-referencing tricks. Packages like natbib, bibliographystyle, and etaremune provide flexible options for customizing how references appear in the final document.

Understanding How Reference Numbers Work in LaTeX

Before diving into how to customize or change reference numbers, it’s important to understand how LaTeX handles references. LaTeX automatically assigns reference numbers based on the order of appearance in the bibliography, which is itself generated by either a manual list using the thebibliography environment or by using tools like BibTeX or BibLaTeX.

By default, when you use \cite{key}, LaTeX inserts a number that corresponds to the numbered entry in the bibliography. Changing this number requires manual intervention or reordering the bibliography itself.

Ways to Change Reference Numbers

1. Manually Setting Reference Numbers

If you are not using BibTeX, one approach is to manually set up your bibliography using the thebibliography environment. This gives you control over the numbering sequence via the optional argument in the \bibitem command.

\begin{thebibliography}{99}
\bibitem[20]{ref1} John Doe. Book Title. Publisher, 2020.
\bibitem[5]{ref2} Jane Roe. Another Work. Journal, 2018.
\end{thebibliography}

Here, the numbers 20 and 5 will appear as reference labels instead of the usual [1], [2], etc.

2. Using the etaremune Package

For those who want to number references in reverse or customize them further, the etaremune package provides enhanced control. It reverses the order and also enables custom labels if combined with other commands.

\usepackage{etaremune}

\begin{etaremune}
\item John Doe. Book Title.
\item Jane Roe. Another Work.
\end{etaremune}

You may still need to cross-reference these manually or using additional macros for full automation.

3. Reordering Citations to Affect Number Assignment

If using BibTeX, LaTeX assigns numbers according to the order of citation in your text. Simply changing the order of \cite{} commands will affect the numbering.

For example, switching:

\cite{smith2020}
\cite{johnson2018}

to:

\cite{johnson2018}
\cite{smith2020}

will change the reference order and consequently the numbering.

4. Creating Custom Citation Commands

Advanced users can define custom citation commands to display any reference label or text. This technique is particularly useful when formatting unique documents where default citation styles do not suffice.

\newcommand{\customcite}[2]{[#1] #2}

% Usage:
\customcite{99}{John Doe, Book Title, 2020}

This won’t link to a bibliography entry, but it’s a straightforward method for inserting stylized references.

Changing the Style of Reference Numbers

Sometimes the goal isn’t to change the reference number itself but the style. For instance, square brackets might need to be replaced with superscripts or parenthesis.

With natbib

The natbib package allows for various citation styles. To change bracket styles, use:

\usepackage[square, numbers]{natbib}

To switch to superscripts:

\usepackage[super]{natbib}

With BibLaTeX

If you’re using BibLaTeX with biber as the backend, you can configure reference numbering via options like:

\usepackage[
  backend=biber,
  style=numeric,
  sorting=none
]{biblatex}
\addbibresource{references.bib}

Custom formatting for labels can be modified using:

\DeclareFieldFormat{labelnumberwidth}{\mkbibbold{#1}}

Best Practices and Tips

• Avoid hardcoding reference numbers: This can disrupt cross-referencing and hyperref compatibility.
• Use packages wisely: Prefer using natbib or BibLaTeX unless you have a specific reason to opt for manual control.
• Automate: Let LaTeX handle citation management wherever possible to reduce errors, especially in long documents.
• Use custom labels sparingly: Custom labels can be difficult to manage as your reference list grows.

Conclusion

Changing reference numbers in LaTeX is completely possible but should be handled with care to maintain the integrity and readability of the document. Depending on the approach—manual, semi-automated, or package-driven—users can customize reference labels and numbers to suit journal requirements, dissertation formatting styles, or personal preferences. Understanding the tooling (BibTeX, BibLaTeX, natbib) and document structure ensures users maintain full control without losing LaTeX’s robust feature set.

FAQ: Changing Reference Numbers in LaTeX

• Q: Can I just type in the number I want for each citation?
  A: While you technically can using custom commands, it’s not advisable. It breaks LaTeX’s automatic referencing features.
• Q: Do I have to use BibTeX or BibLaTeX?
  A: No, but they offer automated citation management that reduces errors and simplifies formatting, especially for large documents.
• Q: How do I reorder reference numbers?
  A: For automatic systems, reorder the \cite{} calls. For manual systems, reorder the \bibitem list.
• Q: Can I use letters or other symbols instead of numbers?
  A: Yes, you can define custom labels with \bibitem[label]{key} or use custom citation commands.
• Q: Will these changes affect my hyperlinks and PDF bookmarks?
  A: Yes, especially when using packages like hyperref. Make sure citation labels are properly linked to ensure navigation remains intact.