# Category: Kids

## ERC panel [step #2]

Another post that was written ages ago, about the second round of the European Research Council (ERC) panel on starting grants for mathematics in which I took part as an expert and not as an applicant. While anonymity possibly fell apart for the several dozens of applicants who were shortlisted for interview, in particular more […]

## Metropolis gets off the ground

An X validated discussion that toed-and-froed about an incomprehension of the Metropolis-Hastings algorithm. Which started with a blame of George Casella‘s and Roger Berger’s Statistical Inference (p.254), when the real issue was the inquisitor having difficulties with the notation V ~ f(v), or the notion of random variable [generation], mistaking identically distributed with identical. Even […]

## no country for old liars

A puzzle from the Riddler about a group of five persons, A,..,E, where all and only people strictly older than L are liars, all making statements about others’ ages: A: B>20 and D>16 B: C>18 and E<20 C: D<22 and A=19 D: E≠20 and B=20 E: A>21 and C<18 The Riddler is asking for the […]

## Le Monde puzzle [#1088]

A board (Ising!) Le Monde mathematical puzzle in the optimisation mode, again: On a 7×7 board, what is the maximal number of locations that one can occupy when imposing at least two empty neighbours ? Which I tried to solve by brute force and simulated annealing (what else?!), first defining a target targ=function(tabz){ sum(tabz[-c(1,9),-c(1,9)]-1.2*(tabz[-c(1,9),-c(1,9)]*tabz[-c(8,9),-c(1,9)] +tabz[-c(1,9),-c(1,9)]*tabz[-c(1,2),-c(1,9)] […]

## (x=scan())%in%(2*4^(n=0:x)-2^n-1)

One challenge on code golf is to find the shortest possible code to identify whether or not an integer belongs to the binary cyclops numbers which binary expansion is 0, 101, 11011, 1110111, 111101111, &tc. The n-th such number being this leads to the above solution in R (26 bits). The same length as the […]

## La peste et la vigne [book review]

During my trip to Cambodia, I read the second volume of this fantasy cycle in French. Which I liked almost as much as the first volume since the author continues to explore the mystery of the central character Syffe and its relations with some magical forces at play in his universe. As in most stories […]

## ERC panel [step #1]

Although this post was written ages ago, regulations of the European Research Council (ERC) prevented me from posting it until now, for confidentiality reasons. I was indeed nominated as an expert member of the ERC panel on starting grants for mathematics [a denomination including statistics, obviously, but also quantum physics or some aspects of it], […]

## sorcerer to the Crown [book review]

Sorcerer to the Crown is an historical fantasy book by Zen Cho I got into buying by reading a review linking most positively it to Jonathan Strange & Mr. Norrell. Obviously I should have known better, given that Jonathan Strange & Mr. Norrell was several years in the making, with both a very convincing reconstitution […]

## per un Rinascimento europeo, pentru o Renaștere europeană, na rzecz europejskiego Odrodzenia, &tc.

[In preparation for the incoming European elections and as a call to arms against populist trends on the rise, Emmanuel Macron has published a tribune in all of the so-far 28 EU countries, written in 24 languages that I aggregated in a single letter, hopefully missing no bit and no language.] Obywatele Europy, wenn ich […]

## per un Rinascimento europeo, pentru o Renaștere europeană, na rzecz europejskiego Odrodzenia, &tc.

[In preparation for the incoming European elections and as a call to arms against populist trends on the rise, Emmanuel Macron has published a tribune in all of the so-far 28 EU countries, written in 24 languages that I aggregated in a single letter, hopefully missing no bit and no language.] Obywatele Europy, wenn ich […]

## Siem Reap conference

As I returned from the conference in Siem Reap. on a flight avoiding India and Pakistan and their [brittle and bristling!] boundary on the way back, instead flying far far north, near Arkhangelsk (but with nothing to show for it, as the flight back was fully in the dark), I reflected how enjoyable this conference […]

## error bars [reposted]

A definitely brilliant entry on xkcd that reflects upon the infinite regress of producing error evaluations that are based on estimates. A must for the next class when I introduce error bars and confidence intervals!

## Le Monde puzzle [#1087]

A board-like Le Monde mathematical puzzle in the digit category: Given a (k,m) binary matrix, what is the maximum number S of entries with only one neighbour equal to one? Solve for k=m=2,…,13, and k=6,m=8. For instance, for k=m=2, the matrix is producing the maximal number 4. I first attempted a brute force random filling […]

## and it only gets worse…

” A recent survey by Bankrate.com found that just 40% of US households have enough money to cover a \$1,000 in emergency expenses.” The Guardian, Feb 2, 2019 ““Until we heard those cheers coming from Albany, we thought states were moving beyond such barbaric practices.” Mr. Pence offered his argument as a litmus test of […]

## simulation fodder for future exams

Here are two nice exercises for a future simulation exam, seen and solved on X validated.The first one is about simulating a Gibbs sampler associated with the joint target exp{-|x|-|y|-a(y-x|} defined over IR² for a≥0 (or possibly a>-1). The conditionals are identical and non-standard, but a simple bound on the conditional density is the corresponding […]

## Le Monde puzzle [#1085]

A new Le Monde mathematical puzzle in the digit category: Given 13 arbitrary relative integers chosen by Bo, Abigail can select any subset of them to be drifted by plus or minus one by Bo, repeatedly until Abigail reaches the largest possible number N of multiples of 5. What is the minimal possible value of […]

## Le Monde puzzle [#1085]

A new Le Monde mathematical puzzle in the digit category: Given 13 arbitrary relative integers chosen by Bo, Abigail can select any subset of them to be drifted by plus or minus one by Bo, repeatedly until Abigail reaches the largest possible number N of multiples of 5. What is the minimal possible value of […]

## Fisher’s lost information

After a post on X validated and a good discussion at work, I came to the conclusion [after many years of sweeping the puzzle under the carpet] that the (a?) Fisher information obtained for the Uniform distribution U(0,θ) as θ⁻¹ is meaningless. Indeed, there are many arguments: The lack of derivability of the indicator function […]