Publications by xi'an
sans sérif & sans chevron
{\sf df=function(x)2*pi*x-4*(x>1)*acos(1/(x+(1-x)*(x<1)))} As I was LaTeXing a remote exam for next week, including some R code questions, I came across the apparent impossibility to use < and > symbols in the sans-sérif “\sf” font… Which is a surprise, given the ubiquity of the symbols in R and my LaTeXing books over the years. Must have ...
1145 sym R (58 sym/1 pcs)
one bridge further
Jackie Wong, Jon Forster (Warwick) and Peter Smith have just published a paper in Statistics & Computing on bridge sampling bias and improvement by splitting. “… known to be asymptotically unbiased, bridge sampling technique produces biased estimates in practical usage for small to moderate sample sizes (…) the estimator yields positive bi...
2342 sym R (187 sym/1 pcs) 4 img
Le Monde puzzle [#1149]
The weekly puzzle from Le Monde is a leaking variant on an old puzzle: Three buckets have capacities of 8, 5 and 3 litres, respectively. At the start of the game, the 8 litre bucket is full and both others are empty. Aiming at reaching exactly 4 litres in one bucket, water is transferred between buckets. However, a fraction 1/k is lost with each...
1087 sym R (224 sym/2 pcs) 2 img
deterministic moves in Metropolis-Hastings
A curio on X validated where an hybrid Metropolis-Hastings scheme involves a deterministic transform, once in a while. The idea is to flip the sample from one mode, ν, towards the other mode, μ, with a symmetry of the kind μ-α(x+μ) and ν-α(x+ν) with α a positive coefficient. Or the reciprocal, -μ+(μ-x)/α and -ν+(ν-x)/α for… rever...
1404 sym R (345 sym/1 pcs) 4 img
Riddle of the lanes
An express riddle from the Riddler about reopening pools, where lanes are allowed provided there is no swimmer in the lane or in any of the adjacent lanes. If swimmers pick their lane at random (while they can), what is the average number of occupied lanes? If there are n lanes and E(n) is the expected number of swimmers, E(n) satisfies a recurre...
886 sym R (159 sym/1 pcs) 2 img
Le Monde puzzle [#1152]
The weekly puzzle from Le Monde is a tournament classic: An even number of teams play one another once a week with no tie allowed and have played all other teams. Four weeks into the tournament, A has won all its games, B,C, and D have won three games, the other teams have won at least one games. What is the minimum number of teams? Show an inst...
1191 sym R (970 sym/2 pcs) 2 img
le compte est bon
The Riddler asks how to derive 24 from (1,2,3,8), with each number appearing once and all operations (x,+,/,-,^) allowed. This reminded me of a very old TV show on French TV, called Le compte est bon!, where players were given 5 or 6 numbers and supposed to find a given total within 60 ,seconds. Unsurprisingly there is an online solver for this g...
1313 sym 4 img
[The Art of] Regression and other stories
CoI: Andrew sent me this new book [scheduled for 23 July on amazon] of his with Jennifer Hill and Aki Vehtari. Which I read in my garden over a few sunny morns. And as Andrew and Aki are good friends on mine, this review is definitely subjective and biased! Hence to take with a spoonful of salt. The “other stories’ in the title is a very nice...
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MCqMC 2020 live and free and online
The MCqMC 20202 conference that was supposed to take place in Oxford next 9-14 August has been turned into an on-line free conference since travelling remains a challenge for most of us. Tutorials and plenaries will be live with questions on Zoom, with live-streaming and recorded copies on YouTube. They will probably be during 14:00-17:00 UK ti...
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the limits of R
It has been repeated many times on many platforms, the R (or R⁰) number is not a great summary about the COVID-19 pandemic, see eg Rossman’s warning in The Conversation, but Nature chose to stress it one more time (in its 16 Jul edition). Or twice when considering a similar piece in Nature Physics. As Boris Johnson made it a central tool of h...
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