Problem with a repository key

To solve the problem with expired PGP key, that spawns this message

W: GPG error: http://ppa.launchpad.net intrepid Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY *key*
W: You may want to run apt-get update to correct these problems

simply run the following in the terminal

gpg --keyserver keyserver.ubuntu.com --recv *key*
gpg --export --armor *key* | sudo apt-key add -

Solution source found here.

centering frametitle in beamer

To center a frametitle (or subtitle) in beamer, simply add this code:

\makeatletter
\long\def\beamer@@frametitle[#1]#2{%
\beamer@ifempty{#2}{}{%
\gdef\insertframetitle{
\centering{#2\ifnum\beamer@autobreakcount>0\relax{}
\space\usebeamertemplate*{frametitle continuation}\fi}}%
\gdef\beamer@frametitle{#2}%
\gdef\beamer@shortframetitle{#1}%
}%
}
\makeatother

Thanks to this thread for this neat solution.

Frames in beamer

There are some useful options for frames in beamer:

[c,t,b] Set vertical alignment (top, center, bottom.)
[fragile] Needed for special text (e.g. verbatim).
[plain] Omit headlines, footlines & sidebar for extra space.
[shrink=n] Shrinks text by n%. This option is very evil.

Options are put behind the {frame}, like:

\begin{frame}[fragile]

The suggestion is from this source.

times and \texttt

Using times fonts in latex

\usepackage{times}

may help to shrink a paper, but screws up the typewriter default font family for Linux users. Putting the following command, will solve the problem:

\renewcommand{\ttdefault}{cmtt}