Text Formatting ⇒ Can I install a pre-update version of Latex?

[sobrio35]

Hi there-
I am still relatively new to Tex. I accepted an update earlier this year which did away with the amsmath package but I haven't had a problem until now. I am trying to write a piecewise function but it won't compile. I was thinking maybe if I went back to an older version I could get it to work. I've been looking and looking online but don't see this particular problem. I also don't really know how the packages work in Latex. Is there a file I download somewhere to get all the features that were previously available in the amsmath package?
Here is a simple version of my code. Maybe it is the problem.

$$
f(x) =
\begin{cases}
p_i & \text{ if k} \equiv 0 \text{ (mod 2)} \\
p_{i+1} & \text{ if k} \equiv 1 \text{ (mod 2)}
\end{cases}
$$

Any ideas?
-Helpless One

[Johannes_B]

You can provide code using the code-button, this way it is clickable in writelatex, see below.
This way, you can find out, if a package version in your document isn't up to date, or the code is wrong.

Code: Select all

\documentclass{article}

\usepackage[english]{babel}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}

\begin{document}
\[f(x) =
\begin{cases}
p_i & \text{ if k} \equiv 0 \text{ (mod 2)} \\
p_{i+1} & \text{ if k} \equiv 1 \text{ (mod 2)}
\end{cases}\]
\end{document}

Please notice, that i used \[ math \] instead of the double dollars, since it is the recommended way of doing in LaTeX.

btw: the safest way to find the cause for errors is preparing a minimal working example.

[sobrio35]

The main problem was I needed a file from the amsmath package which was missing after the update, but I also made the switch from $$ to \[, though I'm not sure what the difference is.
Thanks for the speedy reply! Great forum.

[Johannes_B]

Using $$ <math> $$ is TeX-Syntax, if you are using LaTeX (the format, please be aware of the differences) you should use \[ <math> \]. Using TeX-syntax here can mess up some spacing.
There is something similar for inline math, where $ <math> $ is TeX, and \( <math> \) is LaTeX. But the differences for inline math are not as drastic and most people use the TeX-syntax there as well. There is more behind it, but for now, i think this will suffice. There might be an extended description of the differences over at TeX.SX, but it is currently closed for maintenance.

Feel free to ask more questions.