## echo vulnerable

Posted in Linux with tags , , , on October 3, 2014 by xi'an

Even though most people are now aware of the Shellshock security problem on the bash shell, here is a test to check whether your Unix system is at risk:

env x='() { :;}; echo vulnerable' bash -c 'echo hello'


if the prompt returns vulnerable, it means the system is vulnerable and needs to be upgraded with the proper security patch… For instance running

sudo apt-get update && sudo apt-get install --only-upgrade bash


for Debian/Ubuntu versions. Check Apple support page for Apple OS.

## a weird beamer feature…

Posted in Books, Kids, Linux, R, Statistics, University life with tags , , , , , , , , , , , , on September 24, 2014 by xi'an

As I was preparing my slides for my third year undergraduate stat course, I got a weird error that got a search on the Web to unravel:

! Extra }, or forgotten \endgroup.
\endframe ->\egroup
\begingroup \def \@currenvir {frame}
l.23 \end{frame}
\begin{slide}
?


which was related with a fragile environment

\begin{frame}[fragile]
\frametitle{simulation in practice}
\begin{itemize}
\item For a given distribution $F$, call the corresponding
pseudo-random generator in an arbitrary computer language
\begin{verbatim}
> x=rnorm(10)
> x
[1] -0.021573 -1.134735  1.359812 -0.887579
[7] -0.749418  0.506298  0.835791  0.472144
\end{verbatim}
\item use the sample as a statistician would
\begin{verbatim}
> mean(x)
[1] 0.004892123
> var(x)
[1] 0.8034657
\end{verbatim}
to approximate quantities related with $F$
\end{itemize}
\end{frame}\begin{frame}


but not directly the verbatim part: the reason for the bug was that the \end{frame} command did not have a line by itself! Which is one rare occurrence where the carriage return has an impact in LaTeX, as far as I know… (The same bug appears when there is an indentation at the beginning of the line. Weird!) [Another annoying feature is wordpress turning > into &gt; in the sourcecode environment…]

## new laptop with ubuntu 14.04

Posted in Linux, R, Statistics, University life with tags , , , , on August 14, 2014 by xi'an

As I was getting worried about the chances of survival of my current laptop (bought in emergency upon my return from Kyoto!), I decided to use some available grant money to buy a new laptop without stepping through the emergency square. Thanks to my local computer engineer, Thomas, I found a local dealer selling light laptops with an already installed Ubuntu 14.04… And qwerty (UK) keyboards. Even though the previous move to Kubuntu 12.04 had been seamless, a failed attempt to switch a Mac to Ubuntu a few months later left me wary about buying a computer first and testing later whether or not it was truly Linux compatible. I am therefore quite happy with the switch and grateful to Thomas for the suggestion. I managed to re-compile my current papers and to run my current R codes, plus connect by wireless and read photos from my camera, hence validating the basic operations I primarily require from a computer! And reinstalled KDE. (I am still having difficulties with the size of the fonts in Firefox though. Which do not seem coherent from a tab to the next.) Enough to sacrifice a new sticker to cover the brand on its cover….

## Luke and Pierre at big’MC

Posted in Linux, pictures, Statistics, Travel, University life with tags , , , , , , , , , , , on May 19, 2014 by xi'an

Yesterday, Luke Bornn and Pierre Jacob gave a talk at our big’MC ‘minar. While I had seen most of the slides earlier, either at MCMski IV,  Banff, Leuven or yet again in Oxford, I really enjoyed those talks as they provided further intuition about the techniques of Wang-Landau and non-negative unbiased estimators, leading to a few seeds of potential ideas for even more potential research. For instance, I understood way better the option to calibrate the Wang-Landau algorithm on levels of the target density rather than in the original space. Which means (a) a one-dimensional partition target (just as in nested sampling); (b) taking advantage of the existing computations of the likelihood function; and (b) a somewhat automatic implementation of the Wang-Landau algorithm. I do wonder why this technique is not more popular as a default option. (Like, would it be compatible with Stan?) The impossibility theorem of Pierre about the existence of non-negative unbiased estimators never ceases to amaze me. I started wondering during the seminar whether a positive (!) version of the result could be found. Namely, whether perturbations of the exact (unbiased) Metropolis-Hastings acceptance ratio could be substituted in order to guarantee positivity. Possibly creating drifted versions of the target…

One request in connection with this post: please connect the Institut Henri Poincaré to the eduroam wireless network! The place is dedicated to visiting mathematicians and theoretical physicists, it should have been the first one [in Paris] to get connected to eduroam. The cost cannot be that horrendous so I wonder what the reason is. Preventing guests from connecting to the Internet towards better concentration? avoiding “parasites” taking advantage of the network? ensuring seminar attendees are following the talks? (The irony is that Institut Henri Poincaré has a local wireless available for free, except that it most often does not work with my current machine. And hence wastes much more of my time as I attempt to connect over and over again while there.) Just in connection with IHP, a video of Persi giving a talk there about Poincaré, two years ago:

## Foundations of Statistical Algorithms [book review]

Posted in Books, Linux, R, Statistics, University life with tags , , , , , , , , , , , , , on February 28, 2014 by xi'an

There is computational statistics and there is statistical computing. And then there is statistical algorithmic. Not the same thing, by far. This 2014 book by Weihs, Mersman and Ligges, from TU Dortmund, the later being also a member of the R Core team, stands at one end of this wide spectrum of techniques required by modern statistical analysis. In short, it provides the necessary skills to construct statistical algorithms and hence to contribute to statistical computing. And I wish I had the luxury to teach from Foundations of Statistical Algorithms to my graduate students, if only we could afford an extra yearly course…

“Our aim is to enable the reader (…) to quickly understand the main ideas of modern numerical algorithms [rather] than having to memorize the current, and soon to be outdated, set of popular algorithms from computational statistics.”(p.1)

The book is built around the above aim, first presenting the reasons why computers can produce answers different from what we want, using least squares as a mean to check for (in)stability, then second establishing the ground forFishman Monte Carlo methods by discussing (pseudo-)random generation, including MCMC algorithms, before moving in third to bootstrap and resampling techniques, and  concluding with parallelisation and scalability. The text is highly structured, with frequent summaries, a division of chapters all the way down to sub-sub-sub-sections, an R implementation section in each chapter, and a few exercises. Continue reading

## hiccups or death throes for pangolin?

Posted in Linux, Statistics, Travel, University life with tags , , , on October 25, 2013 by xi'an

Today my Ubuntu system had a strange pathology, almost freezing in any Internet connection, whether using a cable connection or wireless, even ping did not answer and nothing wrong on the process table… I checked the hardware by dual-booting on windows (for the first time since I installed Linux on this laptop) and seeing no such feature on Explorer. After a few reboots, it came back to normal. I wonder if this is an incomplete safety upgrade or a signal that my cheap laptop is coming close to the end of its life cycle. A life started right after Kyoto. Since I am leaving for Pittsburgh and Toronto next week, I should try to re-install a Linux version on another machine this weekend….

## kernel panic: iGoogle will be retired on November 1!!!

Posted in Kids, Linux with tags , on October 6, 2013 by xi'an

On every day, I now get a reminder that iGoogle will be retired in nn days… Terrible deadline looming closer and closer, less than a month now, and I still do not know how to compensate for this retirement! I started using iGoogle quite a while ago for following various RSS threads on newspapers and active blogs like Andrew’s, Rbloggers, and the like. Plus the weather in various parts of the World. In the past few days, I started experimenting with igHome, but it is awfully slow (on my slow machine) and does not reproduce all the apps I used on iGoogle. Nicolas had suggested another substitute I have now forgotten that merged all RSS flows into a single one, which made it unappealing to me… Any suggestion?  Like netvibes? (Maybe this is a good thing in the end, reducing the flow of information and thus temptations to check too many items on the Internet!)