Indices

In some big documents, for example books, it is customary to make an alphabetic list containing the main terms. With LaTeX and the support program imakeidx, an index can be generated quite easily.

Introduction

Let's see a simple working example.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{imakeidx}
\makeindex

\begin{document}
\section{Introduction}
In this example, several keywords\index{keywords} will be used 
which are important and deserve to appear in the Index\index{Index}.

Terms like generate\index{generate} and some\index{others} will 
also show up. 

\printindex
\end{document}

 Open this example in Overleaf

The following image shows the output produced by the example above:

First, the package is included in the preamble by the line

\usepackage{imakeidx}

Then the command \makeindex is mandatory for the index to work and can take some parameters to customize its appearance, in the next sections this will be clear.

To add an entry to the index the command \index{} is used, where the word to be added is inserted as the parameter. Be careful, this won't print the word in the current position but only in the index.

Finally, the command \printindex will actually render the index. If you are using a special localization by means of the babel package, the title will be translated accordingly.

Note: instead of imakeidx, the package makeidx may be imported but offers less customizations possibilities.

Indices on Overleaf

When adding an index to a project on Overleaf, it is important to note that for the index to compile properly, the main .tex file needs to be in the root directory of the project, outside of any folders. This ensures that the auxiliary files needed to generate the index are cached in a way that they are accessible to the compiler.

Entries and sub-entries

As mentioned in the previous section, the command \index will add the word passed to it to the index, but this is not the only way it can be used.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{imakeidx}
\makeindex

\begin{document}
\section{Introduction}
In this example, several keywords\index{keywords} will be used 
which are important and deserve to appear in the Index\index{Index}.

Terms like generate\index{generate} and some\index{others} will also 
show up. Terms in the index can also be nested \index{Index!nested}

\clearpage

\section{Second section}
This second section\index{section} may include some special word, 
and expand the ones already used\index{keywords!used}.

\printindex
\end{document}

 Open this example in Overleaf

The following image shows the output produced by the example above:

It is a common practice to extend terms in the index to include special adjectives. For instance, the word Field may have a special meaning if preceded by the adjective finite or followed by of characteristic 0, and it may be a bit cumbersome to add different types of Fieldas separate entries in the index. For such cases, you can add an exclamation mark "!" that will add the terms after this mark as sub entries of the primary word Field.

In the example, the word "Index" has the word "nested" as sub-entry.

Formatting the Index

Simple formatting for the index, such as changing the index title, adding several columns and changing the column width can be easily done passing optional values to \makeindex:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{imakeidx}
\makeindex[columns=3, title=Alphabetical Index]

\begin{document}
\section{Introduction}
In this example, several keywords\index{keywords} will be used which 
are important and deserve to appear in the Index\index{Index}.

Terms like generate\index{generate} and some\index{others} will also 
show up. Terms in the index can also be nested \index{Index!nested}

\clearpage

\section{Second section}
This second section\index{section} may include some special word, 
and expand the ones already used\index{keywords!used}.

\printindex
\end{document}

 Open this example in Overleaf

The following image shows the output produced by the example above:

In this example, the index is presented in a three-column format with the parameter columns=3, and the title is changed to "Alphabetical Index" by title=Alphabetical Index; these parameters are passed to \makeindex in the preamble. See the reference guide for a list of available parameters and their description.

Using style files

For further customization of the index one can use a style file. Style files inform makeindex about the intended format of the final output. Style files contain a list of <key, value> pairs. For instance, if one needs to group the terms in the index by their initial letter and align the page numbers to the right, the next style file will do the job:

headings_flag 1

heading_prefix "\n\\centering\\large\\sffamily\\bfseries%
\\noindent\\textbf{"heading_suffix "}\\par\\nopagebreak\n"

item_0 "\n \\item \\small "

delim_0 " \\hfill "
delim_1 " \\hfill "
delim_2 " \\hfill "

The keys change different elements in the index output:

• headings_flag 1 enables grouping inserting the group header (symbols, numbers or letters) before a new group.
• heading_prefix formats the header to insert before a new letter begins. It uses regular formatting commands for the font family, font height and alignment, but the backslashes must be escaped using a double backslash instead of one.
• item_0 is what will be inserted between two primary items.
• delim_* is the delimiter to be inserted between the key and the first page number.

For a full list of keys and values to use in a .ist file see The table included in the reference guide.

Assume the previous file is saved as "example_style.ist". To use it in the document we add the parameter options= -s example_style.ist to the \makeindex command.

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{imakeidx}
\makeindex[columns=3, title=Alphabetical Index, 
           options= -s example_style.ist]

\begin{document}

\tableofcontents

\section{Introduction}
In this example, several keywords\index{keywords} will be used which are important and deserve to appear in the Index\index{Index}.

Terms like generate\index{generate}, a great\index{great} list and som other\index{others} terms that might be important\index{important} 
will also show up. Terms in the index can also be nested \index{Index!nested}

\clearpage

\section{Second section}
This second section\index{section} may include some special word, and expand the ones already used\index{keywords!used}. 

\printindex
\end{document}

 Open an example using an index style file on Overleaf

The following image shows the output produced by the example above:

Including the index in the table of contents

By default, the index is not included in the table of contents, this can be easily adjusted.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{imakeidx}
\makeindex[columns=3, title=Alphabetical Index, intoc]

\begin{document}
\tableofcontents

\section{Introduction}
In this example, several keywords\index{keywords} will be 
used which are important and deserve to appear in the 
Index\index{Index}.

Terms like generate\index{generate} and some\index{others} 
will also show up. Terms in the index can also be 
nested \index{Index!nested}

\clearpage

\section{Second section}
This second section\index{section} may include some special 
word, and expand the ones already used\index{keywords!used}.

\printindex
\end{document}

 Open this example in Overleaf

The following image shows the output produced by the example above:

By adding the parameter intoc to the command \makeindex the inclusion of the index title into the table of contents is enabled.

Reference guide

Parameters for the \makeindex command

title

Title to be typeset at the beginning of the specific index. An example is presented in formatting the index.

intoc

If this option is passed, the index title is put in the table of contents.

columns

Uses the syntax key=value, the value must be an integer representing the number of columns. The default value is 2.

columnsep

Specifies units that represent the separation between the columns. The syntax must be key=value, for example columnsep=2em.

columnseprule

If option is passed, a vertical ruler will be rendered between the columns.

Keys to create style files

The next table shows the keys, default values and descriptions to create .ist style files.

Further reading

For more information see:

• Glossaries
• Lists of tables and figures
• Table of contents
• Sections and chapters
• Hyperlinks
• International language support
• Cross referencing sections and equations
• Management in a large project
• Multi-file LaTeX projects
• imakeidx package documentation