Articles by xi'an

Astrostatistics school

October 17, 2017 | xi'an

What a wonderful week at the Astrostat [Indian] summer school in Autrans! The setting was superb, on the high Vercors plateau overlooking both Grenoble [north] and Valence [west], with the colours of the Fall at their brightest on the foliage of the forests rising on both sides of the valley ...
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[summer Astrostat school] room with a view [jatp]

October 9, 2017 | xi'an

I just arrived in Autrans, on the Plateau du Vercors overlooking Grenoble and the view is fabulistic! Trees have started to turn red and yellow, the weather is very mild, and my duties are restricted to teaching ABC to a group of enthusiastic astronomers and cosmologists..! Second advanced course on ... [Read more...]

mea culpa!

October 8, 2017 | xi'an

An entry about our Bayesian Essentials book on X validated alerted me to a typo in the derivation of the Gaussian posterior..! When deriving the posterior (which was left as an exercise in the Bayesian Core), I just forgot the term expressing the divergence between the prior mean and the ... [Read more...]

Le Monde puzzle [#1021]

September 17, 2017 | xi'an

A puzzling Le Monde mathematical puzzle for which I could find no answer in the allotted time!: A most democratic electoral system allows every voter to have at least one representative by having each of the N voters picking exactly m candidates among the M running candidates and setting the ...
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Le Monde puzzle [#1020]

September 14, 2017 | xi'an

A collection of liars in this Le Monde mathematical puzzle: A circle of 16 liars and truth-tellers is such that everyone states that their immediate neighbours are both liars. How many liars can there be? A circle of 12 liars and truth-tellers is such that everyone state that their immediate neighbours are ...
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Le Monde puzzle [#1018]

August 28, 2017 | xi'an

An arithmetic Le Monde mathematical puzzle (that first did not seem to involve R programming because of the large number of digits in the quantity involved): An integer x with less than 100 digits is such that adding the digit 1 on both sides of x produces the integer 99x.  What are ...
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sequence riddle

August 9, 2017 | xi'an

The riddle this week on The Riddler was about finding the largest sequence of integers between 1 and 100 such that each integer is only used once and always followed by a multiple or a factor. A basic R code searching at random [and programmed during a massive downpour on Skye] led ...
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Le Monde puzzle [#1707]

July 27, 2017 | xi'an

A geometric Le Monde mathematical puzzle: Given a pizza of diameter 20cm, what is the way to cut it by two perpendicular lines through a point distant 5cm from the centre towards maximising the surface of two opposite slices?  Using the same point as the tip of the four slices, ...
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RNG impact on MCMC [or lack thereof]

July 12, 2017 | xi'an

Following the talk at MCM 2017 about the strange impact of the random generator on the outcome of an MCMC generator, I tried in Montréal airport the following code on the banana target of Haario et al. (1999), copied from Soetaert and Laine and using the MCMC function of the FME ...
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easy riddle

July 11, 2017 | xi'an

From the current Riddler, a problem that only requires a few lines of code and a few seconds of reasoning. Or not. N households each stole the earnings from one of the (N-1) other households, one at a time. What is the probability that a given household is not burglarised? ...
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[un]solved riddles

July 3, 2017 | xi'an

On the Riddler of last week, first a birthday puzzle: Given a group of 23 persons, what is the probability of observing three pairs of identical birthdays? which can be found by a quick simulation as ave=0 for (t in 1:1e6){ dupz=dates[duplicated(sample(1:365,23,rep=TRUE))] ave=ave+as.integer((...
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thinning a Markov chain, statistically

June 12, 2017 | xi'an

Art Owen has arXived a new version of his thinning MCMC paper, where he studies how thinning or subsampling can improve computing time in MCMC chains. I remember quite well the message set by Mark Berliner and Steve MacEachern in an early 1990’s paper that subsampling was always increasing the ... [Read more...]

datazar

June 3, 2017 | xi'an

A few weeks ago and then some, I [as occasional blogger!] got contacted by datazar.com to write a piece on this data-sharing platform. I then went and checked what this was all about, having the vague impression this was a platform where I could store and tun R codes, ... [Read more...]

continental divide

May 18, 2017 | xi'an

While the Riddler puzzle this week was anticlimactic,  as it meant filling all digits in the above division towards a null remainder, it came as an interesting illustration of how different division is taught in the US versus France: when I saw the picture above, I had to go and ...
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Le Monde puzzle [#1006]

May 2, 2017 | xi'an

Once the pseudo-story [noise] removed, a linear programming Le Monde mathematical puzzle: For the integer linear programming problem max 2x¹+2x²+x³+…+x¹⁰ under the constraints x¹__x²+x³, x²__x³+x⁴, …, x⁹__x¹⁰+x¹, x¹⁰__x¹+x² find a solution with the maximal number of positive entries. Expressed this ...
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a secretary problem with maximum ability

April 27, 2017 | xi'an

The Riddler of today has a secretary problem, where one measures sequentially N random variables until one deems the current variable to be the largest of the whole sample. The classical secretary problem has a counter-intuitive solution where one first measures N/e random variables without taking any decision and ... [Read more...]

Le Monde puzzle [#1003]

April 17, 2017 | xi'an

A purely arithmetic Le Monde mathematical puzzle: Find the four integers w, x, y, z such that the four smallest pairwise sums among the six pairwise sums are 59, 65, 66, and 69. Similarly, find the four smallest of the five integers v, x, y, z such that the five smallest pairwise sums among ...
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optimultiplication [a riddle]

April 13, 2017 | xi'an

The riddle of this week is about an optimisation of positioning the four digits of a multiplication of two numbers with two digits each and is open to a coding resolution: Four digits are drawn without replacement from {0,1,…,9}, one at a time. What is the optimal strategy to position those ... [Read more...]

Statlearn17, Lyon

April 6, 2017 | xi'an

Today and tomorrow, I am attending the Statlearn17 conference in Lyon, France. Which is a workshop with one-hour talks on statistics and machine learning. And which makes for the second workshop on machine learning in two weeks! Yesterday there were two tutorials in R, but I only took the train ... [Read more...]

Le Monde puzzle [#1002]

April 3, 2017 | xi'an

For once and only because it is part of this competition, a geometric Le Monde mathematical puzzle: Given both diagonals of lengths p=105 and q=116, what is the parallelogram with the largest area? and when the perimeter is furthermore constrained to be L=290? This made me jump right away to ...
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