spot the LaTeX mistake

It took me forever to spot the (obvious) mistake in the following LaTeX formula

\int \exp\[ -\{ (n+\sigma^{-2})\mu^2 -2n\mu{\bar x_n} + n ({\bar x_n})^2 \}/2 \]

Can you find it?!

R midterms

Here are my R midterm exams, version A and version B in English (as students are sitting next to one another in the computer rooms), on simulation methods for my undergrad exploratory statistics course. Nothing particularly exciting or innovative! Dedicated ‘Og‘s readers may spot a few Le Monde puzzles in the lot…

Two rather entertaining if mundane occurences related to this R exam: one hour prior to the exam, a student came to my office to beg for being allowed to take the solution manual with her (as those midterm exercises are actually picked from an exercise booklet, some students cooperated towards producing a complete solution manual and this within a week!), kind of missing the main point of having an exam. (I have not seen yet this manual but I’d be quite interested in checking the code they produced on that occasion…) During the exam, another student asked me what was the R command to turn any density into a random generator: he had written a density function called mydens and could not fathom why rmydens(n) was not working. The same student later called me as his computer was “stuck”: he was not aware that a “+” prompt on the command line meant R was waiting for him to complete the command… A less comical event that ended well is that a student failed to save her R code (periodically and) at the end of the exam and we had to dig very deep into the machine to salvage her R commands from \tmp as rkward safeguards, as only the .RData file was available at first. I am glad we found this before turning the machine off, otherwise it would have been lost.

crns.fr!

An email I got today from the CNRS  as forwarded by our computer engineer:

Bonjour,

Merci de prendre le temps de lire ce mail jusqu’au bout.

Nous vous mettons en garde par rapport au nom de domaine crns.fr (notez bien l’inversion des lettres).

Toute connexion ou requête vers une machine du domaine crns.fr, (suite par exemple à une malencontreuse inversion de lettres, erreur pouvant arriver à n’importe qui) aboutit évidemment sur une machine étrangère à notre communauté. Par conséquent, tout login et mot de passe (et toute autre information confidentielle) entrés sur la machine sont susceptibles d’être capturés pour exploitation ultérieure.

En particulier, toute connexion ssh envoyée vers une machine du domaine crns.fr aboutit et DEMANDE UN MOT DE PASSE, **quel que soit le nom de la machine**. Cela est EXTREMEMENT DANGEREUX ! On peut imaginer de la même chose le détournement des mails envoyés à une adresse @crns.fr.

This means that someone did register crns.fr as a valid domain and manages to steal login and password from anyone mistyping crns instead of cnrs…. I find this warning a bit dubious (a phising on hacking?!), the French being approximative and the email using CAPITAL letters, while the possibility of typing c.r.n.s. instead of c.n.r.s. is rather remote, if only because the n is typed by a right finger… Furthermore, if this domain is indeed using this homophony (or whatever is the right term!, anagramity?!) to steal accounts and information,  it should be open to prosecution and be closed (or, better, given to CNRS). However, I checked a fake CNRS subdomain with the inversion and did get the following message

jorasses:~/mybooks/core2$ ssh -X fictious.crns.fr
The authenticity of host 'fictious.crns.fr (176.74.176.167)' can't be established.
ECDSA key fingerprint is 31:88:94:86:cb:88:46:d5:7d:3d:70:a7:15:1a:be:e1.
Are you sure you want to continue connecting (yes/no)?
no
Host key verification failed.

that I obviously did not want to push any further! While I could have entered my true login and password at fictious.crns.fr, this does not mean much per se (even though the crns.fr site looks a wee insecure with all those similar links, it certainly does not try to pretend it is the Cnrs site).

ISBA towards higher computing goals [yet another new section!!!]

Surrounding the great and exciting gathering of Bayesian statisticians in Kyoto last June, several ISBA sections have appeared in the past weeks, as already mentioned on the ‘Og. Along with Anto Mira and Nicolas Chopin (who did most of the organisational work while I was wandering down under!), we discussed about a Bayesian computation section and, thanks to the massive support of the community, we engaged into setting this new section of ISBA, with the help of Peter Green and Håvard Rue. The structure has now been granted an approval stamp by the ISBA highest powers and so here we are with a brand new ISBA Section on Bayesian Computation!!! (A notion I remember discussing with Peter Müller in Valparaiso in…2004!) I think I was the first member to join the section, following the announcement of its official creation by Merlise Clyde… Here is a draft of the call to potential members (along with my own comments):

Over the past twenty years, Bayesian computation has been a tremendous catalyst in Bayesian ideas reaching practitioners – statisticians and non-statisticians alike. It has also providied a fantastic arena for original research in algorithmic statistics and numerical probability, not to mention other fields at the interface. At this more mature stage of its development, at a time where ambitions of statisticians and the expectations on statistics grow, Bayesian computation must remain a major area of research and innovation. Then principled methods of statistical analysis can continue to be both readily available and customarily implemented, as we deal with data on a (much) larger scale, in higher dimensions and with more complex structure.

We invite all ISBA members with (any degree of) interest in computation for Bayesian inference to join the newly created ISBA Section on Bayesian Computation (BayesComp) – and that means both researchers involved in developing new computational methods and associated theory, and users of Bayesian statistical methods interested in implementing, sharing, disseminating, or learning best practice. The purposes of the Section are as multifaceted as the aspects of Bayesian computation, including promoting original research into computational methods for Bayesian inference and decision making, encouraging the use of frontier computational tools among practitioners, the development of adapted software, languages, platforms, and dedicated machines, and translating and disseminating among statisticians methods developed in other disciplines.

To address these purposes, the Section will among other activities organise specific conferences (such as the upcoming MCMSki IV in January 2014), workshops, short courses, webinars, and sessions in other meetings like ISBA and JSM, and will develop and maintain a website of information, tools, and advice as an authoritative central resource for Bayesian computation. The first such resource is already posted: the ISBA Foundation Lecture by Christian Robert on “Approximate Bayesian computation (ABC): Advances and Questions.”[I am definitely not responsible for this inclusion!]

Section dues are only $5 a year or $75 for a Lifetime membership. As part of the Fall (Autumn) Membership Promotion, all new annual memberships will be extended until 31 December, 2013! The section will be holding elections in November, so please join today so that you may participate in choosing the first set of elected officers–and please contact us if you are interested in any of the elected positions! More details to come on the BayesComp section website and the ISBA Bulletin. [You should definitely opt for the Life membership as I did, given that the transaction costs are paid only once! This also means more money for the Section to support younger members towards travel to conferences...]

Welcome to Year 1 BC (BayesComp)!

Nicolas Chopin, Peter Green, Antonietta Mira, Christian Robert and Håvard Rue.

Disas-tea-R at dawn

This was bound to happen sooner or later, given my addiction to tea and sleepless nights, so I eventually managed to spill a cup of tea over my Mac… I had been working for a few hours in my hotel room in Philadelphia, completing an ABC paper with Jean-Michel Marin and Robin Ryder. We had been running experiments in R with Jean-Michel over the past days and I wanted to check some details with him about some graphs he sent me, so we got into a Skype conversation. At the same time, I was running an alternative R code to compare with his, and starting a new ‘Og entry about a current campaign against road accidents. And drinking my fifth or sixth cuppa of the morning. I suddenly realised dawn had come and stood up to raise the blinds next to my desk. Completely forgetting about the earphones on my head. The obvious then occurred: the earphone cord stretched, pulling the teacup over and I turned back to see the keyboard covered with tea… Disaster! I tipped the computer over and grabbed the hotel hairdryer to try to dry it as quickly as possible (apologies to the next room neighbour!). Contrary to all advices, I did not turn the Mac off but kept running the R program instead to add to the heat of the dryer. In retrospect this was quite silly and I am lucky to get out with only two keys not working!