# Typesetting text in math mode (2)

In a previous post (Typesetting text in math mode) I advertised the use of \mbox to write text in mathematical formulas. This works when you are in the "standard size", but looks funny if you have subscripts because the sizes are off:

$50 \mbox{ apples}_{\mbox{yellow}} \times 100 \mbox{ apples}_{\mbox{red-green}} = \mbox{lots of apples}^{\mbox{to eat}}$


looks like
$50 \mbox{ apples}_{\mbox{yellow}} \times 100 \mbox{ apples}_{\mbox{red-green}} = \mbox{lots of apples}^{\mbox{to eat}}$

In these cases (and also in the standard cases but there it looks the same), you can use the command \text which will come out in the right font size. In addition to just \text, there is also \textbf (bold face), \textit (italics) and \texttt (typewriter).

$50 \text{ apples}_{\text{yellow}} \times 100 \textit{ apples}_{\texttt{red-green}} = \textbf{lots of apples}^\text{to eat}$


looks like
$50 \text{ apples}_{\text{yellow}} \times 100 \textit{ apples}_{\texttt{red-green}} = \textbf{lots of apples}^\text{to eat}$

Note: Most of the time \text should just work in math mode without any packages, but for some distributions you need to explicitly load the package amstext or amsmath.

# Undefined references – LaTeX Warning

Sometimes LaTeX tells you this:

LaTeX Warning: There were undefined references.


If you get this warning, you will notice some ?? in your document at places where references should be. For references to sections, tables of figures, just run pdflatex again (and check for typos). For bibliography references you need to run bibtex.

Let’s assume you are writing a LaTeX file with the name ‘report.tex’. Do the following:

> pdflatex report.tex
[...]
LaTeX Warning: Citation Liu2010' on page 1 undefined on input line 39.
[...]
LaTeX Warning: Reference fig:results' on page 1 undefined on input line 65.
[...]
LaTeX Warning: There were undefined references.
[...]
LaTeX Warning: Label(s) may have changed. Rerun to get cross-references right.
[...]
> bibtex report
[...]
> pdflatex report.tex
[...]
LaTeX Warning: Label(s) may have changed. Rerun to get cross-references right.
[...]
> pdflatex report.tex
[...]


You need to run pdflatex again twice after calling bibtex. Twice, because layout may change and things end up somewhere else after you inserted the references.

# Installing a LaTeX package

Let’s say you want to create a A0 poster with LaTeX. You find an example on the internet that starts like this:

\documentclass[final]{beamer}
\usepackage[orientation=landscape,size=a0,scale=1]{beamerposter}
\usepackage{lipsum} % lorem ipsum


You download the example ‘example.tex’, run pdflatex on it and it fails like this:

me@mycomputer: pdflatex example.tex
This is pdfTeX, Version 3.1415926-2.3-1.40.12 (TeX Live 2011)
restricted \write18 enabled.
entering extended mode
(./example.tex
LaTeX2e <2011/06/27>
Babel  and hyphenation patterns for english, dumylang, nohyphenation, lo
(/usr/share/texlive/texmf-dist/tex/latex/beamer/beamer.cls

[...]

Type X to quit or  to proceed,
or enter new name. (Default extension: sty)

Enter file name:


This means, that this particular LaTeX package ‘beamerposter’ is not installed on your machine. Bad luck.

## What to do if you have admin permissions

On linux, open your favourite package manager (e.g., Synaptic), type the name of the LaTeX package (in this case ‘beamerposter’). If the result shows a linux package like ‘texlive-latex-extra’ install it and be happy.

## What to do if you do not have admin permissions

Go to CTAN. Search for the missing package name and click on the best result. In the beamerposter case, you will end up here. To get to a page where you can actually download the package, you need to follow the link listed under CTAN path in the box at the bottom of the page. Click on ‘Download’ and save the ‘beamerposter.zip’ somewhere on your computer.

We will also assume that the second package, ‘lipsum’, is also missing, you would find it on CTAN here.

### 2. Extract the package to the correct location

The READMEs of LaTeX package usually contain "Put it in your tex folder" or "Put it somewhere where LaTeX can find it" (if they contain anything on installation at all). What this actually means is, that there are several possibilities. LaTeX searches for sources in a few directories, depending on your system and LaTeX distribution. Some examples for linux and texlive are:

/usr/share/texmf/
/usr/share/texlive/texmf/
/usr/local/share/texmf/tex/latex/
~/texmf/


If you don’t have admin permissions, the easiest is to create a folder ‘texmf’ in your home directory (~). You will need in this folder a subfolder ‘tex’, and then ‘latex’. So in total you should have:

~
|- texmf/
|- tex
|- latex


In this folder, i.e., ~/texmf/tex/latex/, you can put any style files and latex will find them. It is advisable to create separate folders for separate packages, so we will extract the ‘beamerposter.zip’ that we downloaded into the folder ~/texmf/tex/latex/beamerposter/ and ‘lipsum.zip’ into the folder ~/texmf/tex/latex/lipsum/. This is what the folder looks like now:

~
|- texmf/
|- tex
|- latex
|- beamerposter
|- beamerposter.pdf
|- beamerposter.sty
|- beamerposter.tex
|- example.tex
|- lipsum
|- lipsum.dtx
|- lipsum.ins
|- lipsum.pdf


As you can see, we now have a ‘beamerposter.sty’. So if this were the only package we needed, we could skip step 3. Unfortunately we are still missing ‘lipsum.sty’, so this is what step 3 is about.

### 3. Create a style file

As we see, there is no style file ‘lipsum.sty’. There is only a ‘lipsum.ins’ and a ‘lipsum.dtx’ file. The .dtx file is only to create the documentation and we can ignore it here. To create the style file, run latex (latex, not pdflatex!) on ‘lipsum.ins’:

me@mycomputer: latex lipsum.ins


The result should look like this:

~
|- texmf/
|- tex
|- latex
|- beamerposter
|- ...
|- lipsum
|- lipsum.dtx
|- lipsum.ins
|- lipsum.log
|- lipsum.pdf
|- lipsum.sty


### 4. Try pdflatex again

And it should work (unless of course a different package is missing…).

## Updating the Database

If you install fonts and in some other cases you need to update the LaTeX package database. On linux/texlive this is done with ‘texhash’:

me@mycomputer: texhash


## More

This works for regular LaTeX packages. Bibtex packages go to texmf/bibtex. If there are fonts involved, you will need to put them in texmf/fonts and it might get tricky.

# Typesetting text in math mode

In information retrieval and text classification, tf-idf plays a big role. Read the Wikipedia article to learn what it is about, here I want to deal with the problem of typesetting the formula in LaTeX.

The formula is log-weighted term frequency tf times inverse document frequency idf, if we naivly write this down, we arrive at this:

tf-idf_{t,d} = (1 +\log tf_{t,d}) \cdot \log \frac{N}{df_t}


When you look at the LaTeX output, you will see that several things go wrong. In math mode, LaTeX interprets two letters next to each other as a product of two variables. So the name tf becomes the mathematical expression “t times f” and is typeset accordingly. Also, in case of tf-idf, the name contains a hyphen. In math mode a hyphen between two expression is interpreted as a minus sign. So this is definitely not what we want.

How do we solve the problem? What we want is that this part is interpreted as normal text. One possibility to add text to equations is the command \mbox{} (another is the command \text{} which requires the amsmath package). So this is it:

\mbox{tf-idf}_{t,d} = (1 +\log \mbox{tf}_{t,d}) \cdot \log \frac{N}{\mbox{df}_t}`