Articles by xi'an

Latent Gaussian Models in Zürich [day 1]

February 4, 2011 | xi'an

An interesting first day (for me) at the Latent Gaussian Models workshop in Zürich. The workshop is obviously centred at the INLA approach, with Havard Rue giving a short course on Wednesday then a wide ranging tour of the applications and extensions of INLA this afternoon. Thanks to his ... [Read more...]

Le Monde puzzle [#4]

February 4, 2011 | xi'an

A fairly simple puzzle in this weekend Le Monde magazine: given five points on a line such that their pairwise distances are 1,2,4,…,14,18,20, find the respective positions of the five points over the line and deduce the missing distances. Without loss of generality, we can set the first point at 0 and ... [Read more...]

ABC model choice not to be trusted [3]

January 30, 2011 | xi'an

On Friday, I received a nice but embarrassing email from Xavier Didelot. He indeed reminded me that I attended the talk he gave at the model choice workshop in Warwick last May, as, unfortunately but rather unsurprisingly giving my short span memory!, I had forgotten about it! Looking at the ...
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R exam

January 30, 2011 | xi'an

I spent most of my Saturday perusing R codes to check the answers written by my students to the R exam I gave two weeks ago… The outcome is mostly poor, even though some managed to solve a fair part of the long problem. Except for the few hopeless cases ... [Read more...]

ABC model choice not to be trusted [2]

January 27, 2011 | xi'an

As we were completing our arXiv summary about ABC model choice, we were helpfully pointed to a recent CRiSM tech. report by X. Didelot, R. Everitt, A. Johansen and D. Lawson on  Likelihood-free estimation of model evidence. This paper is quite related to our study of the performances of the ...
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ABC model choice not to be trusted

January 26, 2011 | xi'an

This may sound like a paradoxical title given my recent production in this area of ABC approximations, especially after the disputes with Alan Templeton, but I have come to the conclusion that ABC approximations to the Bayes factor are not to be trusted. When working one afternoon in Park City ...
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Trip to Lyon

January 20, 2011 | xi'an

This was my first trip to Lyon in about… 35 years, I think, but I did not have much time to tour the city! My original plan was to go climbing with Ivan near La Meije right after the talk, but our respective knees were hurting for the past week at ...
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The ultimate exam excuse…

January 19, 2011 | xi'an

A few days after my R exam (available in French here), I received this email from the department secretary: Pour information cet étudiant est venu me trouver jeudi soir, catastrophé car il venait de constater que son stylo “PILOT Frixion”, stylo semble-t-il recommandé par certains enseignants, ne se contentait pas ... [Read more...]

Séminaire à Lyon

January 17, 2011 | xi'an

Next week, I am going to Lyon to give a seminar in Université Lyon I. I will talk about the recent Rao-Blackwellisation papers we wrote, hopefully managing to make sense with both statisticians and probabilists, unlike in recent talks of mine in probability seminars… The slides are close to those ...
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Introducing Monte Carlo Methods with R [precision]

January 17, 2011 | xi'an

Doug Rivers, professor of Political Sciences in Stanford, kindly sent me this email yesterday night: The 2nd displayed equation in section 2.1.2 on p. 44 is garbled (it might be interpreted as saying that U and X have the same distribution). I think you intended: And indeed we should have stated the ...
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Méthodes de Monte-Carlo avec R [out]

January 17, 2011 | xi'an

The translation of the book Introducing Monte Carlo Methods with R is now published and out! I have received five copies in the mail yesterday, although it was not produced in time for my R class students to get it before the exam today. The book is still indicated on ...
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Missing reference in Monte Carlo Statistical Methods

January 15, 2011 | xi'an

A few days ago, Peng Yu sent me this email Dear Prof. Robert, The citation Edwards and Sokal (1988) appears on page 326 of your book MCSM2. However, I don’t find in in the Reference section (it would have appear on page 601 if it is in the reference section). I don’...
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CosmoPMC released

January 12, 2011 | xi'an

Martin Kilbinger, an astronomer (cosmologist) with whom we had worked on population Monte Carlo for cosmological inference [during the ANR-05-BLAN-0283- 04 ANR ECOSSTAT grant], has made the PMC C codes available on the CosmoPMC webpage. He has also written a CosmoPMC manual that is now available from arXiv. And ...
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Two short Bayesian courses in South’pton

January 12, 2011 | xi'an

An announcement for two short-courses on Introduction to  Bayesian Analysis and MCMC, and Hierarchical Modelling of Spatial and Temporal Data by Alan Gelfand (Duke University, USA) and Sujit Sahu (University of Southampton, UK), are to take place in Southampton on June 7-10, this year. Course 1: Introduction to Bayesian Analysis and ... [Read more...]

Le Monde puzzle [1]

January 10, 2011 | xi'an

Following the presentation of the first Le Monde puzzle of the year, I tried a simulated annealing solution on an early morning in my hotel room. Here is the R code, which is unfortunately too rudimentary and too slow to be able to tackle n=1000. #minimise \sum_{i=1}^I x_... [Read more...]

Arrogance sampling

January 7, 2011 | xi'an

A new posting on arXiv by Benedict Escoto on a simulation method for approximating normalising constants (i.e. evidence) with an eye-catching name! Here is the abstract This paper describes a method for estimating the marginal likelihood or Bayes factors of Bayesian models using non-parametric importance sampling (“arrogance sampling”). This ... [Read more...]

a survey on ABC

January 6, 2011 | xi'an

With Jean-Michel Marin, Pierre Pudlo and Robin Ryder, we just completed a survey on the ABC methodology. It is now both arXived and submitted to Statistics and Computing. Rather interestingly, our first draft was written in Jean-Michel’s office in Montpelier by collating the ‘Og posts surveying new ABC papers! (...
[Read more...]

Short review of the R book

January 5, 2011 | xi'an

David Scott wrote a review of Introducing Monte Carlo Methods with R in the International Statistical Review that is rather negative, since the main bulk reads as follows: I found some aspects of the book very disappointing. The first chapter (“Basic R Programming”) has some unfortunate mistakes and some statements, ...
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Adap’skiii [day 2]

January 5, 2011 | xi'an

Another exciting day at Adap’skiii!!! Yves Atchadé presented a very recent work on the fundamental issue of estimating the asymptotic variance estimation for adaptive MCMC algorithms, with an intriguing experimental observation that a non-converging bandwidth with rate 1/n was providing better coverage than the converging rate. (I always found ...
[Read more...]

Le Monde puzzle [52|solution]

January 1, 2011 | xi'an

I have now received the first issue of Le Monde magazine, including the solution to puzzle #52 I solved just in time by simulated annealing! The trick is in using the following theorem: Iter(1,x,y) is divisible by 10x-1 if and only if y is divisible by 10x-1. Then the ... [Read more...]
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