Archive for Bretagne

Kempner Fi

Posted in Books, Kids, R, Statistics with tags , , , , , , , on January 19, 2021 by xi'an

A short code-golf challenge led me to learn about the Kempner series, which is the series made of the inverted integers, excluding all those containing the digit 9. Most surprisingly this exclusion is enough to see the series converging (close to 23). The explanation for this convergence is that, citing Wikipedia,

“The number of n-digit positive integers that have no digit equal to ‘9’ is 8 × 9n−1

and since the inverses of these n-digit positive integers are less than 101−n the series is bounded by 80. In simpler terms, it converges because the fraction of remaining terms in the series is geometrically decreasing as (9/10)1−n. Unsurprisingly (?) the series is also atrociously slow to converge (for instance the first million terms sum up to 11) and there exist recurrence representations that speed up its computation.  Here is the code-golf version

n=scan()+2
while(n<-n-1){
F=F+1/T
while(grepl(9,T<-T+1))0}
F

that led me to learn about the R function grepl. (The explanation for the pun in the title is that Semper Fidelis is the motto of the corsair City of Saint-Malo or Sant-Maloù, Brittany.)

poor statistics

Posted in Books, pictures, R, Statistics, Travel, Wines with tags , , , , , , , , , , , , on September 24, 2019 by xi'an

I came over the weekend across this graph and the associated news that the county of Saint-Nazaire, on the southern border of Brittany, had a significantly higher rate of cancers than the Loire countries. The complete study written by Solenne Delacour, Anne Cowppli-Bony, amd Florence Molinié, is quite cautious about the reasons for this higher rate, even using a Bayesian Poisson-Gamma smoothing (and the R package empbaysmooth), and citing the 1991 paper by Besag, York and Mollié, but the local and national medias are quick to blame the local industries for the difference. The graph above is particularly bad in that it accumulates mortality causes that are not mutually exclusive or independent. For instance, the much higher mortality rate due to alcohol is obviously responsible for higher rates of most other entries. And indicates a sociological pattern that may or may not be due to the type of job in the area, but differs from the more rural other parts of the Loire countries. (Which, like Brittany, are already significantly above (50%) the national reference for alcohol related health issues.), and may not be strongly connected to exposition to chemicals. For instance, the rates of pulmonary cancers are mostly comparable to the national average, if higher than the rest of the Loire countries and connect with a high smoking propensity. Lymphomas are not significantly different from the regional reference. The only type of cancer that can be directly attributed to working conditions are the mesothelioma, mostly caused by asbestos exposure, which was used in ship building, a specialty of the area. Among the many possible reasons for the higher mortality of the county, the study mentions a lower exposure to medical testings (connected with the sociological composition of the area). Which would indicate the most effective policies for lowering these higher cancer and mortality rates.

the Kouign-Amann experiment

Posted in Kids, pictures, Travel with tags , , , , , , , on June 10, 2019 by xi'an

Having found a recipe for Kouign-Amanns, these excessive cookies from Britanny that are essentially cooked salted butter!, I had a first try that ended up in disaster (including a deep cut on the remaining thumb) and a second try that went better as both food and body parts are concerned. (The name means cake of butter in Breton.)The underlying dough is pretty standard up to the moment it starts being profusedly buttered and layered, again and again, until it becomes sufficiently feuilleté to put in the oven. The buttery nature of the product, clearly visibly on the first picture, implies the cookies must be kept in containers like these muffin pans to preserve its shape and keep the boiling butter from  inundating the oven, two aspects I had not forecasted on the first attempt.The other if minor drawback of these cookies is that they do not keep well as they contain so much butter. Bringing enough calories input for an hearty breakfast (and reminding me of those I ate in Cambridge while last visiting Pierre).

indecent exposure

Posted in Statistics with tags , , , , , , , , , , , , on July 27, 2018 by xi'an

While attending my last session at MCqMC 2018, in Rennes, before taking a train back to Paris, I was confronted by this radical opinion upon our previous work with Matt Moores (Warwick) and other coauthors from QUT, where the speaker, Maksym Byshkin from Lugano, defended a new approach for maximum likelihood estimation using novel MCMC methods. Based on the point fixe equation characterising maximum likelihood estimators for exponential families, when theoretical and empirical moments of the natural statistic are equal. Using a Markov chain with stationary distribution the said exponential family, the fixed point equation can be turned into a zero divergence equation, requiring simulation of pseudo-data from the model, which depends on the unknown parameter. Breaking this circular argument, the authors note that simulating pseudo-data that reproduce the observed value of the sufficient statistic is enough. Which is related with Geyer and Thomson (1992) famous paper about Monte Carlo maximum likelihood estimation. From there I was and remain lost as I cannot see why a derivative of the expected divergence with respect to the parameter θ can be computed when this divergence is found by Monte Carlo rather than exhaustive enumeration. And later used in a stochastic gradient move on the parameter θ… Especially when the null divergence is imposed on the parameter. In any case, the final slide shows an application to a large image and an Ising model, solving the problem (?) in 140 seconds and suggesting indecency, when our much slower approach is intended to produce a complete posterior simulation in this context.

Rennes street art #2 [jatp]

Posted in Kids, pictures, Travel, University life with tags , , , , , , , , , on July 7, 2018 by xi'an