Blog Archives

a grim knight [cont’d]

October 19, 2016
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a grim knight [cont’d]

As discussed in the previous entry, there are two interpretations to this question from The Riddler: “…how long is the longest path a knight can travel on a standard 8-by-8 board without letting the path intersect itself?” as to what constitutes a path. As a (terrible) chess player, I would opt for the version on

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ratio-of-uniforms

October 19, 2016
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ratio-of-uniforms

One approach to random number generation that had always intrigued me is Kinderman and Monahan’s (1977) ratio-of-uniform method. The method is based on the result that the uniform distribution on the set A of (u,v)’s in R⁺xX such that 0≤u²≤ƒ(v/u) induces the distribution with density proportional to ƒ on V/U. Hence the name. The proof

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an attempt at EP-ABC from scratch, nothing more… [except for a few bugs]

October 18, 2016
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an attempt at EP-ABC from scratch, nothing more… [except for a few bugs]

Following a request from one of the reviewers of our chapter Likelihood-free model choice, I tried to run EP-ABC on a toy problem and to compare it with the outcome of a random forest ABC. Literally starting from scratch, namely from the description found in Simon and Nicolas’ JASA paper.  To run my test, I

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tractable Bayesian variable selection: beyond normality

October 16, 2016
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tractable Bayesian variable selection: beyond normality

David Rossell and Francisco Rubio (both from Warwick) arXived a month ago a paper on non-normal variable selection. They use two-piece error models that preserve manageable inference and allow for simple computational algorithms, but also characterise the behaviour of the resulting variable selection process under model misspecification. Interestingly, they show that the existence of asymmetries

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grim knight [a riddle]

October 13, 2016
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grim knight [a riddle]

The Riddler of this week had a riddle that is a variation of the knight tour problem, namely “…how long is the longest path a knight can travel on a standard 8-by-8 chessboard without letting the path intersect itself?” the riddle being then one of a self-avoiding random walk … As I could not get

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importance sampling by kernel smoothing [experiment]

October 12, 2016
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importance sampling by kernel smoothing [experiment]

Following my earlier post on Delyon and Portier’s proposal to replacing the true importance distribution ƒ with a leave-one-out (!) kernel estimate in the importance sampling estimator, I ran a simple one-dimensional experiment to compare the performances of the traditional method with this alternative. The true distribution is a N(0,½) with an importance proposal a N(0,1)

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Journal of Open Source Software

October 3, 2016
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Journal of Open Source Software

A week ago, I received a request for refereeing a paper for the Journal of Open Source Software, which I have never seen (or heard of) before. The concept is quite interesting with a scope much broader than statistical computing (as I do not know anyone in the board and no-one there seems affiliated with

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approximate lasso

October 2, 2016
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approximate lasso

Here is a representation of the precision of a kernel density estimate (second axis) against the true value of the density (first axis), which looks like a lasso of sorts, hence the title. I am not sure this tells much, except that the estimated values are close to the true values and that a given

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an inverse permutation test

September 22, 2016
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an inverse permutation test

A straightforward but probabilistic riddle this week in the Riddler, which is to find the expected order of integer i when the sequence {1,2,…,n} is partitioned at random into two sets, A and B, each of which is then sorted before both sets are merged. For instance, if {1,2,3,4} is divided in A={1,4} and B={2,3},

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astroABC: ABC SMC sampler for cosmological parameter estimation

September 5, 2016
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astroABC: ABC SMC sampler for cosmological parameter estimation

“…the chosen statistic needs to be a so-called sufficient statistic in that any information about the parameter of interest which is contained in the data, is also contained in the summary statistic.” Elise Jenningsa and Maeve Madigan arXived a paper on a new Python code they developed for implementing ABC-SMC, towards astronomy or rather cosmology

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