**A**s every odd year, the Royal Statistical Society is seeking a new joint editor for Series B! After four years of dedication to the (The!) journal, Piotr Fryzlewicz is indeed going to retire from this duty by the end of 2017. Many thanks to Piotr for his unfailing involvement in Series B and the preservation of its uncompromising selection of papers! The call thus open for candidates for the next round of editorship, from 2018 to 2021, with a deadline of 31 January, 2017. Interested candidates should contact Martin Owen, at the Society’s address or by email at rss.org.uk with journal as recipient (local-part). The new editor will work with the current joint editor, David Dunson, whose term runs till December 2019. (I am also looking forward working with Piotr’s successor in developing the Series B blog, Series’ Blog!)

## a new Editor for Series B

Posted in Statistics with tags blog, JRSSB, Royal Statistical Society, Series B on January 16, 2017 by xi'an## incredible India

Posted in Kids, Mountains, pictures, Running, Travel with tags air pollution, Bengali food, cash-free economy, cellphone, child labour, Darjeeling, ghee, India, Kolkata, panipuri, pollution, puri, Ravi Shankar, street food, traffic on January 15, 2017 by xi'an*[The following is a long and fairly naïve rant about India and its contradiction, without pretence at anything else than writing down some impressions from my last trip. JATP: Just another tourist post!]*

Incredible India (or Incredible !ndia) is the slogan chosen by the Indian Ministry of Tourism to promote India. And it is indeed an incredible country, from its incredibly diverse landscapes [and not only the Himalayas!] and eco-systems, to its incredibly huge range of languages [although I found out during this trip that the differences between Urdu and Hindi are more communitarian and religious than linguistic, as they both derive from Hindustani, although the alphabets completely differ] and religions [a mixed blessing], to its incredibly rich history and culture, to its incredibly wide offer of local cuisines [as shown by the Bengali sample below, where the mustard seed fish cooked in banana leaves and the fried banana flowers are not visible!] and even wines [like Sula Vineyards, which offers a pretty nice Viognier]. Not to mention incredibly savoury teas from Darjeeling and Assam. Continue reading

## la maison des mathématiques

Posted in Books, Kids, pictures, Statistics, University life with tags Akashic Books, book review, exhibit, IHP, Institut Henri Poincaré, la maison des mathématiques, Paris, photograph, Vincent Moncorgé on January 14, 2017 by xi'an**W**hen I worked with Jean-Michel Marin at Institut Henri Poincaré the week before Xmas, there was this framed picture standing on the ground, possibly in preparation for exhibition in the Institute. I found this superposition of the lady cleaning the blackboard from its maths formulas and of the seemingly unaware mathematician both compelling visually in the sheer geometric aesthetics of the act and somewhat appalling in its message. Especially when considering the initiatives taken by IHP towards reducing the gender gap in maths. After inquiring into the issue, I found that this picture was part of a whole photograph exhibit on IHP by Vincent Moncorgé, now published into a book, La Maison des Mathématiques by Villani, Uzan, and Moncorgé. Most pictures are on-line and I found them quite appealing. Except again for the above.

## principal components [xkcd repost]

Posted in Kids with tags bike path, cat, data analysis, lint, pi, principal components, taxes, xkcd on January 13, 2017 by xi'an## Le Monde puzzle [#990]

Posted in Books, Kids, pictures, Statistics, Travel, University life with tags binary, intToBits(), Le Monde, mathematical puzzle, R on January 12, 2017 by xi'an**T**o celebrate the new year (assuming it is worth celebrating!), Le Monde mathematical puzzle came up with the following:

Two sequences (x¹,x²,…) and (y¹,y²,…) are defined as follows: the current value of x is either the previous value or twice the previous value, while the current value of y is the sum of the values of x up to now. What is the minimum number of steps to reach 2016 or 2017?

B*y* considering that all consecutive powers of 2 must appear at least one, the puzzles boils down to finding the minimal number of replications in the remainder of the year minus the sum of all powers of 2. Which itself boils down to deriving the binary decomposition of that remainder. Hence the basic R code (using intToBits):

deco=function(k=2016){ m=trunc(log2(k)) while (sum(2^(0:m))>k) m=m-1 if (sum(2^(0:m))==k){ return(rep(1,m+1)) }else{ res=k-sum(2^(0:m)) return(rep(1,m+1)+as.integer(intToBits(res))[1:(m+1)])

which produces

> sum(deco(2016)) [1] 16 > sum(deco(2017)) [1] 16 > sum(deco(1789)) [1] 18

## anytime algorithm

Posted in Books, Statistics with tags anytime algorithm, Cambridge University, computing cost, exchangeability, Harvard University, MCMC, SMC, SMC², University of Oxford, University of Warwick on January 11, 2017 by xi'an**L**awrence Murray, Sumeet Singh, Pierre Jacob, and Anthony Lee (Warwick) recently arXived a paper on Anytime Monte Carlo. (The earlier post on this topic is no coincidence, as Lawrence had told me about this problem when he visited Paris last Spring. Including a forced extension when his passport got stolen.) The difficulty with anytime algorithms for MCMC is the lack of exchangeability of the MCMC sequence (except for formal settings where regeneration can be used).

When accounting for duration of computation between steps of an MCMC generation, the Markov chain turns into a Markov jump process, whose stationary distribution α is biased by the average delivery time. Unless it is constant. The authors manage this difficulty by interlocking the original chain with a secondary chain so that even- and odd-index chains are independent. The secondary chain is then discarded. This provides a way to run an anytime MCMC. The principle can be extended to K+1 chains, run one after the other, since only one of those chains need be discarded. It also applies to SMC and SMC². The appeal of anytime simulation in this particle setting is that resampling is no longer a bottleneck. Hence easily distributed among processors. One aspect I do not fully understand is how the computing budget is handled, since allocating the same real time to each iteration of SMC seems to envision each target in the sequence as requiring the same amount of time. (An interesting side remark made in this paper is the lack of exchangeability resulting from elaborate resampling mechanisms, lack I had not thought of before.)