Rennes street art [jatp]

self-portrait on a railway board [jatp]

MissData 2015 in Rennes [June 18-19]

This (early) summer, a conference on missing data will be organised in Rennes, Brittany, with the support of the French Statistical Society [SFDS]. (Check the website if interested, Rennes is a mere two hours from Paris by fast train.)

art brut

trip to Besançon (and the stars)

Today, I made a quick TGV trip to Besançon, in French Jura, to give a seminar to astronomers and physicists, in connection with the Gaia project I had mentioned earlier. I gave my talk straight out of the train and then we started discussing MCMC and ABC for the astronomy problems my guests face. To my surprise, I discovered that they do run some local form of ABC, using their own statistics and distances to validate simulation from the (uniform) prior on their parameter space. The discussion went far enough to take a peek under the hood, namely to look at some Fortran programs they are running (and make suggestions for acceleration and adaptation). It is quite interesting to see that ABC is actually a natural approach when people face complex likelihoods and that, while they construct appropriate tools, they feel somehow uncertain about the validation of those methods and are unaware of very similar tools in other fields. In addition to this great day of exchange, I had several hours of freedom in the train (and a plug) to work on the bayess package for Bayesian Essentials (not dead yet!). Here are my slides, pot-pourri of earlier talks. (Including the one on cosmology model choice in Vancouver.)

High speed trains in Britain

I read an article in the Economist about (and against) high speed trains in Britain. It is eloquently entitled “the great train robbery” and in the tradition of the Economist, opposes this type of government interventions. In the current case, the issue is rather poorly argued! For instance, “the trend in France has been for headquarters to move up the line to Paris and for fewer overnight stays elsewhere”: I am afraid this trend started around Louis XIV’s time, the French TGV did not aggravate a strong Jacobin characteristic of French politics and sociology, the predominant role of Paris. On the other hand, the fast train connections to Marseille, Lilles, or Bordeaux means day trips are possible by train rather than plane. The article does not mention the Channel tunnel project, a state-funded venture if any, that made plane travel between Paris and London a thing from the past and twinned both cities by a two hour trip so much that going shopping from one place to the other sounds completely natural (to my kids if not to me!). Similarly, “China’s safety failures have shown the perils of skimping in any way” does not apply everywhere (while I agree that the precipitation China showed in building such an immense fast-speed network is not unrelated with the recent crash). Moreover, the idea that “upgrading existing, slower networks often makes more sense” is fine as long as companies are willing to invest in the long term. But the story of British railways shows the opposite, namely that companies are looking at short-term profits and balk at those long-term investments. Only states can provoke changes at this scale, so of course “ordinary taxpayers end up paying”. But they would pay in other ways for extending road networks or existing airports, or for maintaining isolated commercial hubs. While the Economist is admitting that “Victorian railways ushered in a golden age of prosperity”, I wonder how it could have supported railways constructions in the 1800’s!