In the motivating toy example to our ABC model choice paper, we compare summary statistics, mean, median, variance, and… median absolute deviation (mad). The latest is the only one able to discriminate between our normal and Laplace models (as now discussed on Cross Validated!). When rerunning simulations to produce nicer ... [Read more...]

Following the question on dinner table permutations on StackExchange (mathematics) and the reply that the right number was six, provided by hardmath, I was looking for a constructive solution how to build the resolvable 2-(20,5,1) covering. A few hours later. hardmath again came up with an answer, found in the ... [Read more...]

Paulo (from the Instituto de Matemática e Estatística, Universidade de São Paulo, Brazil) has posted an answer to my earlier question both as a comment on the ‘Og and as a solution on StackOverflow (with a much more readable LaTeX output). His solution is based on the ... [Read more...]

Wondering about the question I posted on Friday (on StackExchange, no satisfactory answer so far!), I looked further at the special case of the gamma distribution I suggested at the end. Starting from the moment conditions, and the solution is (hopefully) given by the system The resolution of this system ... [Read more...]

On Tuesday, Eric Chi and Kenneth Lange arXived a paper on a comparison of numerical techniques for solving sudokus. (The very Kenneth Lange who wrote this fantastic book on numerical analysis.) One of these techniques is the simulated annealing approach I had played with a long while ago.  They seem ... [Read more...]

I was grading my Master projects this morning and came upon this graph: which compares the variability of an importance-sampling estimator versus its self-normalised alternative… This is an interesting case in that self-normalisation does considerably degrade the quality of the approximation in that setting. In other cases, self-normalisation may bring ... [Read more...]

It has been a wonderful week in Roma, a mix of pleasant work and enjoyable free-time! I gave the ABC advanced course for the second time in a month so it did not require much in terms of preparation and there was a good sized audience with attentive (if too ... [Read more...]

Here are the R codes of the second R lab organised by Serena Arima in supplement of my lectures (now completed!). This morning I covered ABC model choice and the following example is the benchmark used in the course (and in the paper) about the impact of summary statistics. (Warning! ... [Read more...]

Here are the R codes of the R labs organised by Serena Arima in supplement of my lectures. This is quite impressive and helpful to the students, as illustrated by the first example below (using the abc software). I am having a great time teaching this “ABC in Roma” course, ... [Read more...]

IntroductionThis post is a work in progress building on the previous post. It's my attempt to simultaneously learn Amazon's AWS tools and set up R and Rstudio Server on a customized "cloud" instance. I look forward to testing some R jobs that have la... [Read more...]

I just put a fresh install of Ubuntu Server (10.04.4 LTS) on one of our machines.  As I was doing some post-install config, I accidentally installed Rstudio Server.  And subsequently fell down an exciting little rabbit-hole of server configur... [Read more...]

Today, I am going to Rome for a week, teaching my PhD course on ABC I first gave in Paris. The course takes place in La Sapienza Università di Roma, from Monday till Thursday. There will be an R lab in addition to the lectures. (I have no further item ... [Read more...]

Large-scale Inference by Brad Efron is the first IMS Monograph in this new series, coordinated by David Cox and published by Cambridge University Press. Since I read this book immediately after Cox’ and Donnelly’s Principles of Applied Statistics, I was thinking of drawing a parallel between the two books. ... [Read more...]

An X’idated reader of Monte Carlo Statistical Methods had trouble with our Example 3.13, the very one our academic book reviewer disliked so much as to “diverse [sic] a 2 star”. The issue is with computing the integral when f is the Student’s t(5) distribution density. In our book, we ... [Read more...]

When I ran I was expecting the same output as So this means that the dummy index in R “for” loops cannot be tweaked that easily. I seem to remember doing this kind of (dirty) tricks with earlier versions… Now, Alessandra and Robin think this is a good thing that ... [Read more...]

Another problem generated by X’validated (on which I spent much too much time!): given an unbiased coin that produced M heads in the first M tosses, what is the expected number of additional tosses needed to get N (N__M) consecutive heads? Consider the preliminary question of getting a ... [Read more...]

After many delays and exchanges of emails, our AMIS paper with Jean-Marie Cornuet, Jean-Michel Marin and Antonietta Mira eventually made it into the Scandinavian Journal of Statistics. I am quite glad it is now published as it will publicize the method... [Read more...]

Next Thursday (Jan. 16), at the RSS, there will be a special half-day meeting (afternoon, starting at 13:30) on Recent Advances in Monte Carlo Methods organised by the General Application Section. The speakers are Richard Everitt, University of Oxford, Missing data, and what to do about it Anthony Lee, Warwick University, Auxiliary ... [Read more...]

Over the weekend, I have added a few slides referring to recent papers mentioning the convergence of ABC algorithms, in particular the very relevant paper by Dean et al. I had already discussed in an earlier post. (This is taking a larger chunk of my time than expected! I am ... [Read more...]

My Paris colleague (and fellow-runner) Aurélien Garivier has produced an interesting comparison of 4 (or 6 if you consider scilab and octave as different from matlab) computer languages in terms of speed for producing the MLE in a hidden Markov model, using EM and the Baum-Welch algorithms. His conclusions are that ... [Read more...]