# Category: Kids

## Le Monde puzzle [#1110]

A low-key sorting problem as Le Monde current mathematical puzzle: If the numbers from 1 to 67 are randomly permuted and if the sorting algorithm consists in picking a number i with a position higher than its rank i and moving it at the correct i-th position, what is the maximal number of steps to […]

## 9 pitfalls of data science [book review]

I received The 9 pitfalls of data science by Gary Smith [who has written a significant number of general public books on personal investment, statistics and AIs] and Jay Cordes from OUP for review a few weeks ago and read it on my trip to Salzburg. This short book contains a lot of anecdotes and […]

## Le Monde puzzle [#1109]

A digital problem as Le Monde current mathematical puzzle: Noble numbers are such that they only involve different digits and are multiple of all their digits. What is the largest noble number? Hmmmm…. Brute force? Since the maximal number of digits is 10, one may as well try: k=soz=9 for (t in 1:1e3){ sol=1 while […]

## an independent sampler that maximizes the acceptance rate of the MH algorithm

An ICLR 2019 paper by Neklyudov, Egorov and Vetrov on an optimal choice of the proposal in an independent Metropolis algorithm I discovered via an X validated question. Namely whether or not the expected Metropolis-Hastings acceptance ratio is always one (which it is not when the support of the proposal is restricted). The paper mentions […]

## trailers versus mountaineers?

A slight altercation in a swimming corridor during lunch put me back into this Le Monde paper I read yesterday about (real?!) mountaineers being annoyed at trailers, especially those currently running the Ultra-Trail du Mont Blanc (UTMB). A lady stopped me from going further for not crawling as this was a “crawl only” lane and […]

## my likelihood is dominating my prior [not!]

An interesting misconception read on X validated today, with a confusion between the absolute value of the likelihood function and its variability. Which I have trouble explaining except possibly by the extrapolation from the discrete case and a confusion between the probability density of the data [scaled as a probability] and the likelihood function [scale-less]. […]

## and it only gets worse [verbatim]

““We do so much for Sweden but it doesn’t seem to work the other way around. Sweden should focus on its real crime problem.” DT, 25 July “The Justice Department upholds the rule of law—and we owe it to the victims and their families to carry forward the sentence imposed by our justice system.” William […]

## prime suspects [book review]

I was contacted by Princeton University Press to comment on the comic book/graphic novel Prime Suspects (The Anatomy of Integers and Permutations), by Andrew Granville (mathematician) & Jennifer Granville (writer), and Robert Lewis (illustrator), and they sent me the book. I am not a big fan of graphic book entries to mathematical even less than […]

## turning forty…

The previous days have been rather tough thanks to another heat wave over Europe, with the temperatures at home reaching above 40⁰ (outside) yesterday afternoon and more importantly not getting under 30⁰ inside the house at night, as there was no wind at al to cool it down. (Except in the basement  where I ended […]

## turning forty…

The previous days have been rather tough thanks to another heat wave over Europe, with the temperatures at home reaching above 40⁰ (outside) yesterday afternoon and more importantly not getting under 30⁰ inside the house at night, as there was no wind at al to cool it down. (Except in the basement  where I ended […]

## record of a spaceborn few [book review]

As in the previous two volumes, the cover of this Becky Chambers’ book is quite alluring. As is the title. The story is a medley of intermingled individual stories revolving (!) around the Exodus Fleet, the massive spaceship that humans boarded to escape a dying Earth. The universe of this third volume in the Wayfarer […]

## Gibbs sampling with incompatible conditionals

An interesting question (with no clear motivation) on X validated wondering why a Gibbs sampler produces NAs… Interesting because multi-layered: The attached R code indeed produces NAs because it calls the Negative Binomial Neg(x¹,p) random generator with a zero success parameter, x¹=0, which automatically returns NAs. This can be escaped by returning a one (1) […]

## a chance (?) encounter

As I was cycling to Paris Dauphine, a few days ago, I spotted someone sitting on a bench and working on a laptop who suspiciously looked like… Andrew Gelman! As I knew Andrew was in Paris that week, and as we were reasonably close to Dauphine, this did not sound like a zero probability event. […]

## The Long, Cruel History of the Anti-Abortion Crusade [reposted]

[Excerpts from an editorial in the NYT of John Irving, American author of the Cider House Rules novel we enjoyed reading 30 years ago] “(…) I respect your personal reasons not to have an abortion — no one is forcing you to have one. I respect your choice. I’m pro-choice — often called pro-abortion by […]

## a non-riddle

Unless I missed a point in the last riddle from the Riddler, there is very little to say about it: Given N ocre balls, N aquamarine balls, and two urns, what is the optimal way to allocate the balls to the urns towards drawing an ocre ball with no urn being empty? Both my reasoning […]

## and it only gets worse [verbatim]

“Increasing export capacity from the Freeport LNG project is critical to spreading freedom gas throughout the world by giving America’s allies a diverse and affordable source of clean energy” M. Menezes, US Secretary of Energy “NASA should NOT be talking about going to the Moon – We did that 50 years ago. They should be […]

## Le Monde puzzle [#1107]

A light birthday problem as Le Monde mathematical puzzle: Each member of a group of 35 persons writes down the number of those who share the same birth-month and the number of those who share the same birth-date [with them]. It happens that these 70 numbers include all integers from 0 to 10. Show that […]

## Le Monde puzzle [#1105]

Another token game as Le Monde mathematical puzzle: Archibald and Beatrix play with a pile of n>100 tokens, sequentially picking m tokens from the pile with m being a prime number [including m=1] or a multiple of 6, the winner taking the last tokens. If Beatrix knows n and proposes to Archibald to start, what […]