LaTeX: \include vs. \input

LaTeX, a typesetting system widely used for the production of scientific and mathematical documents, provides users with various commands to include external files. Two of the most commonly used commands for this purpose are \include and \input. While both serve the same fundamental purpose of incorporating external content into a LaTeX document, they have distinct characteristics that make them suitable for different scenarios.

Introduction to \include and \input

\include

The \include command is primarily designed for managing larger documents by allowing users to split their work into multiple files. This command is often used for including chapters or sections of a document, making it a valuable tool for organizing extensive projects such as books or theses.

\documentclass{article}
\begin{document}
\include{chapter1}
\include{chapter2}
% ... additional chapters
\end{document}

\input

On the other hand, \input is a more straightforward command that directly includes the content of the specified file at the point where the command is issued. It is suitable for smaller documents or when you want to include specific portions of a file.

\documentclass{article}
\begin{document}
\input{introduction}
\input{methodology}
% ... additional sections
\end{document}

Differences between \include and \input

Compilation Efficiency

One key distinction between \include and \input lies in how they handle compilation. The \include command generates separate .aux files for each included file, allowing for more efficient compilation of individual sections. This can significantly reduce compilation times for large documents.

Page Breaks

Another significant difference is the handling of page breaks. The \include command always starts a new page for the included content, making it ideal for chapters. In contrast, \input does not introduce a page break, making it suitable for including smaller sections within the same page.

Best Practices and Use Cases

Use Cases for \include

• Large Documents: \include is the preferred choice for extensive projects like books, theses, or reports, where breaking the content into separate files enhances manageability.
• Faster Compilation: When compilation time is a concern, especially for large documents, \include can provide a noticeable improvement in efficiency.

Use Cases for \input

• Small Documents: For shorter documents or when including specific sections, \input is a more straightforward and convenient choice.
• No Page Break Required: When you want to seamlessly integrate content without introducing a new page, \input is the better option.

Combining \include and \input

In some cases, users may find it beneficial to combine both \include and \input within the same document. For instance, a large document with several chapters might benefit from using \include for each chapter and \input to include specific subsections or details within those chapters.

\documentclass{book}
\begin{document}
\include{chapter1}
\input{section1_1}
\input{section1_2}
\include{chapter2}
% ... additional chapters and sections
\end{document}

This hybrid approach allows for a hierarchical structure, maintaining the benefits of efficient compilation and page breaks provided by \include while leveraging the simplicity and direct inclusion capabilities of \input.

Using \includeonly

LaTeX also offers the \includeonly command, which allows users to specify which files should be included during compilation. This can be particularly useful when working on specific sections of a large document, avoiding the need to compile the entire document each time.

\documentclass{book}
\includeonly{chapter1, section1_1}
\begin{document}
\include{chapter1}
\input{section1_1}
% ... additional chapters and sections
\end{document}

By using \includeonly, you can speed up compilation by including only the relevant sections during development without removing or commenting out other parts of the document.

File Extensions and Paths

When using \include and \input, it’s essential to note that file extensions are optional. LaTeX automatically appends common extensions like .tex, so specifying the extension is usually unnecessary. Additionally, you can provide relative or absolute paths to the files, allowing for a flexible project structure.

% Relative path
\include{./chapters/chapter1}

% Absolute path
\input{/path/to/your/document/appendix}

Error Handling and Debugging

Understanding how LaTeX processes files with \include and \input is crucial for effective error handling. If there are issues with included files, LaTeX will generate helpful error messages indicating the problematic file. Paying attention to these messages can streamline the debugging process.