““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 Barr, Attorney General, 25 July

“And you had the Nobel Prize? That’s incredible. They gave it to you for what reason?” DT, 17 July

“Why don’t they go back and help fix the totally broken and crime infested places from which they came.” DT, 14 July

“Donald Trump is responsible for this. He is responsible because he is stoking fears and hatred and bigotry. He is responsible because he is failing to condemn white supremacy, and seeing it as it is.” Corry Booker, 4 August

## Archive for the Kids Category

## and it only gets worse [verbatim]

Posted in Kids with tags America, baby Trump, cliffs, death penalty, Donald Trump, Dover cliffs, gun control, justice, mass shooting, Nobel Peace Prize, racism, Sweden, Together Against Trump, US politics, US presidents, World Coalition against the death penalty, Yazidis on August 14, 2019 by xi'an## Kudzu [クズ] delicacies [jatp]

Posted in Kids, pictures, Travel with tags クズ, Japan, Japanese cuisine, jatp, kudzu, kuzu, macha tea, Nara, starch, Tengyokudo Nara shop on August 12, 2019 by xi'an## prime suspects [book review]

Posted in Books, Kids, University life with tags Alexandre Grothendieck, book review, CHANCE, comics, François Schuiten, Gödel Escher and Bach, graphic novel, Jacques Tardi, José Muñoz, Kingman's coalescent, logicomix, NCIS, Nicolas Bourbaki, Persi Diaconis, Princeton University Press on August 6, 2019 by xi'an

**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 to statistical notions (Logicomix being sort of an exception for its historical perspective and nice drawing style) and this book did nothing to change my perspective on the subject. First, the plot is mostly a pretense at introducing number theory concepts and I found it hard to follow it for more than a few pages. The [noires maths] story is that “forensic maths” detectives are looking at murders that connects prime integers and permutations… The ensuing NCIS-style investigation gives the authors the opportunity to skim through the whole cenacle of number theorists, plus a few other mathematicians, who appear as more or less central characters. Even illusory ones like Nicolas Bourbaki. And Alexander Grothendieck as a recluse and clairvoyant hermit [who in real life did not live in a Pyrénées cavern!!!]. Second, I [and nor is Andrew who was in my office when the book arrived!] am not particularly enjoying the drawings or the page composition or the colours of this graphic novel, especially because I find the characters drawn quite inconsistently from one strip to the next, to the point of being unrecognisable, and, if it matters, hardly resembling their real-world equivalent (as seen in the portrait of Persi Diaconis). To be completely honest, the drawings look both ugly and very conventional to me, in that I do not find much of a characteristic style to them. To contemplate what Jacques Tardi, François Schuiten or José Muñoz could have achieved with the same material… (Or even Edmond Baudoin, who drew the strips for the graphic novels he coauthored with Cédric Villani.) The graphic novel (with a prime 181 pages) is postfaced with explanations about the true persons behind the characters, from Carl Friedriech Gauß to Terry Tao, and of course on the mathematical theory for the analogies between the prime and cycles frequencies behind the story. Which I find much more interesting and readable, obviously. (With a surprise appearance of Kingman’s coalescent!) But also somewhat self-defeating in that so much has to be explained on the side for the links between the story, the characters and the background heavily loaded with “obscure references” to make sense to more than a few mathematician readers. Who may prove to be the core readership of this book.

There is also a bit of a Gödel-Escher-and-Bach flavour in that a piece by Robert Schneider called Réverie in Prime Time Signature is included, while an Escher’s infinite stairway appears in one page, not far from what looks like Milano Vittorio Emmanuelle gallery (On the side, I am puzzled by the footnote on p.208 that “I should clarify that selecting a random permutation and a random prime, as described, can be done easily, quickly, and correctly”. This may be connected to the fact that the description of Bach’s algorithm provided therein is incomplete.)

*[Disclaimer about potential self-plagiarism: this post or an edited version will eventually appear in my Books Review section in CHANCE. As appropriate for a book about Chance!]*

## turning forty…

Posted in Kids, pictures with tags Antony, climate change, Europe, Harry Potter, heat wave, J.K. Rowlings, Parc de Sceaux, swimming pool on July 26, 2019 by xi'an**T**he previous days have been rather tough thanks to another heat wave all 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 all to cool it down. (Except in the basement where I ended up sleeping.) After a certain point, as I am pretty susceptible to hot weather, working became impossible and I spent the rest of the day alternating between drinking cold water, taking cold showers, eating radishes, and watching low intensity movies (like The Crimes of Grindelwald!). The day before, my daughter and I tried a late afternoon trip to the nearby outside pool in the parc but this proved quite a disaster as it was so crowded that it was almost impossible to do laps (in a water of questionable composition). Temperatures are now down a wee bit but I wondering at ways to better insulate our house against what is becoming the new “normal”…. Like installing a massive circus tent every summer.

## Gibbs sampling with incompatible conditionals

Posted in Books, Kids, R, Statistics with tags convergence of Gibbs samplers, cross validated, incompatible conditionals, NAs, null recurrence, R, transience on July 23, 2019 by xi'an**A**n 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) instead.
- The Gibbs sampler is based on a Bin(x²,p) conditional for X¹ and a Neg(x¹,p) conditional for X². When using the most standard version of the Negative Binomial random variate as the number of failures, hence supported on 0,1,2…. these two conditionals are incompatible, i.e., there cannot be a joint distribution behind that returns these as conditionals, which makes the limiting behaviour of the Markov chain harder to study. It however seems to converge to a distribution close to zero, which is not contradictory with the incompatibility property: the stationary joint distribution simply does not enjoy the conditionals used by the Gibbs sampler as its conditionals.
- When using the less standard version of the Negative Binomial random variate understood as a number of attempts for the conditional on X², the two conditionals are compatible and correspond to a joint measure proportional to , however this pmf does not sum up to a finite quantity (as in the original Gibbs for Kids example!), hence the resulting Markov chain is at best null recurrent, which seems to be the case for p different from ½. This is unclear to me for p=½.

## so long, Johnny Clegg!

Posted in Kids with tags apartheid, Johannesburg, Johnny Clegg, Juluka, Le Zoulou Blanc, Scaterlings Of Africa, South Africa on July 17, 2019 by xi'an