Publications by xi'an
random wake
Just too often on X validated, one sees questions displaying a complete ignorance of the basics that makes one purposelessly wonder what is the point of trying to implement advanced methods when missing the necessary background. And just as often, I reacted to the question by wondering out loud about this… In the current case, the question was ...
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cyclic riddle [not in NYC!]
In the riddle of this week on fivethirtyeight, the question is to find the average number of rounds when playing the following game: P=6 players sitting in a circle each have B=3 coins and with probability 3⁻¹ they give one coin to their right or left side neighbour, or dump the coin to the centre. The game ends when all coins are in the centr...
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correlation for maximal coupling
An interesting (if vaguely formulated) question on X validated: given two Gaussian variates that are maximally coupled, what is the correlation between these variates? The answer depends on the parameters of both Gaussian, with a correlation of one when both Gaussians are identical. Answering the question by simulation (as I could not figure out ...
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Le Monde puzzle [#1036]
An arithmetic Le Monde mathematical puzzle to conclude 2017: Find (a¹,…,a¹³), a permutation of (1,…,13) such that a¹/a²+a³=a²+a³/a³+a⁴+a⁵=b¹<1 a⁶/a⁶+a⁷=a⁶+a⁷/a⁷+a⁸+a⁹=a⁷+a⁸+a⁹/a⁵+a⁹+a¹⁰=b²<1 a¹¹+a¹²/a¹²+a¹³=a¹²+a¹³/a¹³+a¹⁰=b³<1 The question can be solved by brute force simulatio...
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Le Monde puzzle [#1037]
A purely geometric Le Monde mathematical puzzle this (or two independent ones, rather): Find whether or not there are inscribed and circumscribed circles to a convex polygon with 2018 sides of lengths ranging 1,2,…,2018. In the first (or rather second) case, the circle of radius R that is tangential to the polygon and going through all nodes...
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València summer school
In another continuation of the summer of Bayesian conferences in Europe, the Universidat de Valencià is organising a summer school on Bayesian statistics, from 16 July till 20 July, 2018. Which thus comes right after our summer school on computational statistics at Warwick. With a basic course on Bayesian learning (2 days). And a more advanced c...
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weakly informative reparameterisations
Our paper, weakly informative reparameterisations of location-scale mixtures, with Kaniav Kamary and Kate Lee, got accepted by JCGS! Great news, which comes in perfect timing for Kaniav as she is currently applying for positions. The paper proposes a unidimensional mixture Bayesian modelling based on the first and second moment constraints, since...
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a one-chance meeting [puzzle]
This afternoon, I took a quick look at the current Riddler puzzle, which sums up as, given three points A, B, C, arbitrarily moving on a plane with a one-shot view of their respective locations, find a moving rule to bring the three together at the same point at the same time. And could not spot the difficulty. The solution seems indeed obvious w...
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StanCon in Helsinki [29-31 Aug 2018]
As emailed to me by Aki Vehtari, the next StanCon will take place this summer in the wonderful city of Helsinki, at the end of August. On Aalto University Töölö Campus precisely. The list of speakers and tutorial teachers is available on the webpage. (The only “negative point” is that the conference does not include a Tuesday, the night of...
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uniform on the sphere [or not]
While looking at X validated questions, I came upon this comment that simulating a uniform distribution on a d-dimensional unit sphere does not proceed from generating angles at random on (0,2π) and computing spherical coordinates… Which I must confess would have been my initial suggestion! This is obvious, nonetheless, when computing the Jaco...
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