Articles by xi'an

implementing reproducible research [short book review]

July 14, 2014 | xi'an

As promised, I got back to this book, Implementing reproducible research (after the pigeons had their say). I looked at it this morning while monitoring my students taking their last-chance R exam (definitely last chance as my undergraduate R course is not reconoduced next year). The book is in fact ... [Read more...]

Le Monde puzzle [#875]

July 11, 2014 | xi'an

I learned something in R today thanks to Le Monde mathematical puzzle: A two-player game consists in A picking a number n between 1 and 10 and B and A successively choosing and applying one of three transforms to the current value of n n=n+1, n=3n, n=4n, starting with ...
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ABC in Cancún

July 10, 2014 | xi'an

Here are our slides for the ABC [very] short course Jean-Michel and I give at ISBA 2014 in Cancún next Monday (if your browser can manage Slideshare…) Although I may switch the pictures from Iceland to Mexico, on Sunday, there will be not much change on those slides we both ... [Read more...]

Efficient Ragged Arrays in R and Rcpp

July 3, 2014 | xi'an

When is R Slow, and Why? Computational speed is a common complaint lodged against R. Some recent posts on r-bloggers.com have compared the speed of R with some other programming languages [1], and showed the favorable impact of the new compiler package on run-times [2]. I and others have written about ... [Read more...]

recycling accept-reject rejections (#2)

July 1, 2014 | xi'an

Following yesterday’s post on Rao’s, Liu’s, and Dunson’s paper on a new approach to intractable normalising constants, and taking advantage of being in Warwick, I tested the method on a toy model, namely the posterior associated with n Student’s t observations with unknown location parameter μ ... [Read more...]

R/Rmetrics in Paris [alas!]

June 29, 2014 | xi'an

Today I gave a talk on Bayesian model choice in a fabulous 13th Century former monastery in the Latin Quarter of Paris… It is the Collège des Bernardins, close to Jussieu and Collège de France, unbelievably hidden to the point I was not aware of its existence despite ... [Read more...]

ABC model choice by random forests

June 24, 2014 | xi'an

After more than a year of collaboration, meetings, simulations, delays, switches,  visits, more delays, more simulations, discussions, and a final marathon wrapping day last Friday, Jean-Michel Marin, Pierre Pudlo,  and I at last completed our latest collaboration on ABC, with the central arguments that (a) using random forests is a ... [Read more...]

revenge of the pigeons

June 23, 2014 | xi'an

While I had not had kamikaze pigeons hitting my windows for quite a while…, it may be that one of them decided to move to biological warfare: when I came back from Edinburgh, my office at the University was in a terrible state as a bird had entered through a ... [Read more...]

trying to speed up Metropolis… and failing!

June 12, 2014 | xi'an

A while ago (but still after Iceland since I used the thorn rune as a math symbol!), I wrote the following post draft as a memo. Now that Marco Banterle, Clara Grazian and myself have completed our delayed acceptance paper, it may be of interest to some readers to see ... [Read more...]

Statistical modeling and computation [apologies]

June 11, 2014 | xi'an

In my book review of the recent book by Dirk Kroese and Joshua Chan,  Statistical Modeling and Computation, I mistakenly and persistently typed the name of the second author as Joshua Chen. This typo alas made it to the printed and on-line versions of the subsequent CHANCE 27(2) column. I am ... [Read more...]

checking for finite variance of importance samplers

June 10, 2014 | xi'an

Over a welcomed curry yesterday night in Edinburgh I read this 2008 paper by Koopman, Shephard and Creal, testing the assumptions behind importance sampling, which purpose is to check on-line for (in)finite variance in an importance sampler, based on the empirical distribution of the importance weights. To this goal, the ... [Read more...]

Tools for Online Teaching

May 30, 2014 | xi'an

Last semester (Fall 2014), I organized and taught an interdisciplinary, collaborative class titled Probability for Scientists. Getting 4 separate teachers on the same page was a challenge, but as scientists we're used to communicating over email, and ... [Read more...]

estimation of deformations of densities

May 21, 2014 | xi'an

Today, Jean-Michel Loubes from Toulouse gave a seminar in Dauphine on the estimation of deformations using Wassertsein distances. This is functional data analysis, where samples from random transforms of the original density are observed towards estimating the baseline (or true) measure As a neophyte, I found the problem of interest ... [Read more...]

understanding complex and large industrial data (UCLID 2014)

May 15, 2014 | xi'an

Just received this announcement of the UCLID 2014 conference in Lancaster, July 1-2 2014: Understanding Complex and Large Industrial Data 2014, or UCLID, is a workshop which aims to provide an opportunity for academic researchers and industrial practitioners to work together and share ideas on the fast developing field of ‘big data’ analysis. ... [Read more...]

the Flatland paradox

May 12, 2014 | xi'an

Pierre Druilhet arXived a note a few days ago about the Flatland paradox (due to Stone, 1976) and his arguments against the flat prior. The paradox in this highly artificial setting is as follows:  Consider a sequence θ of N independent draws from {a,b,1/a,1/b} such that N and θ are ...
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terrible graph of the day

May 12, 2014 | xi'an

A truly terrible graph in Le Monde about overweight and obesity in the EU countries (and Switzerland). The circle presentation makes no logical sense. Countries are ordered by 2030 overweight percentages, which implies the order differs for men and women. (With a neat sexist differentiation between male and female figures.)  The ...
[Read more...]

stopping rule impact

May 8, 2014 | xi'an

Here is a question from my friend Shravan Vasishth about the consequences of using a stopping rule: Psycholinguists and psychologists often adopt the following type of data-gathering procedure: The experimenter gathers n data points, then checks for significance (p [Read more...]

Le Monde puzzle [#865]

May 5, 2014 | xi'an

A Le Monde mathematical puzzle in combinatorics: Given a permutation σ of {1,…,5}, if σ(1)=n, the n first values of σ are inverted. If the process is iterated until σ(1)=1, does this always happen and if so what is the maximal  number of iterations? Solve the same question for the set {1,…,2014}. I ran the ...
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RSS statistical analytics challenge 2014

May 1, 2014 | xi'an

Great news! The RSS is setting a data analysis challenge this year, sponsored by the Young Statisticians Section and Research Section of the Royal Statistical Society: Details are available on the wordpress website of the Challenge. Registration is open and the Challenge goes live on Tuesday 6 May 2014 for an exciting 6 ... [Read more...]

Le Monde puzzle [#869]

April 26, 2014 | xi'an

A Le Monde mathematical puzzle once again in a Sudoku mode: In an nxn table, all integers between 1 and n appear n times. If max denotes the maximum over the numbers of different integers on all rows and columns,  what is the minimum value of max when n=7? when n=11? ...
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