## Xing glass bridges [or not]

Posted in Books, Kids, pictures, R, Statistics with tags , , , , , , , on November 10, 2021 by xi'an

A riddle from the Riddler surfing on Squid Games. Evaluating the number of survivors (out of 16 players) able to X the glass bridge, when said bridge is made of 18 consecutive steps, each involving a choice between a tempered and a non-tempered glass square. Stepping on a non-tempered square means death, while all following players are aware of the paths of the earlier ones. Each player thus moves at least one step further than the previous and unlucky player. The total number of steps used by the players is therefore a Negative Binomial Neg(16,½) variate truncated at 19 (if counting attempts rather than failures), with the probability of reaching 19 being .999. When counting the number of survivors, a direct simulation gives an estimate very close to 7:

`   mean(apply(apply(matrix(rgeom(16*1e6,.5)+1,nc=16),1,cumsum)>18,2,sum))`

but the expectation is not exactly 7! Indeed, this value is a sum of probabilities that the cumulated sums of Geometric variates are larger than 18, which has no closed form as far as I can see

`   sum(1-pnbinom(size=1:16,q=17:2,prob=.5)`

but whose value is 7.000076. In the Korean TV series, there are only three survivors, which would have had a .048 probability of occurring. (Not accounting for the fact that one player was temporarily able to figure out which square was right and that two players fell through at the same time.)

Looking later at on-line discussions, I found that the question was quite popular, with a whole spectrum of answers… Including a wrong Binomial B(18, ½) modelling that does not account for the fact that all 16 (incredibly unlucky) players could have died before the last steps.

And reading the solution on The Riddler a week later, I was sorry to see this representation of the distribution of survivors, as if it was a continuous distribution!

## squid games

Posted in Books, pictures with tags , , , , , , , , , , on October 30, 2021 by xi'an

Following my son’s prodding, I watched the Korean series Squid Games a few weeks ago, before it became a worldwide phenomenon, as illustrated by the French national public radio, France Inter, hosting a talk show with a philosopher and a psychiatrist on the layers of the game! And the French Ministry of Education warning primary and secondary school headmasters of the dangers of copycats in the playgrounds… My overall impression was one of originality with comparison with other K drama series I had watched, even though the realistic early scenes of a deeply indebted and failed father reminded me of several of them, not to mention the beginning of Parasite. The switch to the game playground was much less convincing, with the military organisation of the guards rather caricaturesque, growing worse with the appearance of the fromt row (?) evilmaster, and hitting ludicrous levels with the depraved male clients from all over the World. It seems to me that the series was trying to mix too many layers in its motivations, from the Korean debt culture, to organ trafficking, to keeping family structures, which made the result unconclusive and unsatisfactory. It sounded too artificial to be really dystopic. And knowing most of the characters were going to die (sorry for the spoiler!) did not help in relating to them. But overall I fail to see why this easy twist of children games is such a danger for humanity. Or carrying any deep message to the World. After all, The Most Dangerous Game did not change the course of history!

## journal of the [second] plague year [away]

Posted in Books, Kids, Mountains, pictures, Travel, University life, Wines with tags , , , , , , , , , , , , , , , on June 12, 2021 by xi'an

Read Fred Vargas’s Seeking Whom He May Devour (L’Homme à l’envers), which I found on a bookshelf of our vacation rental in Annecy. And got more quickly bored by the story as it is plagued with the same defects as the ones I read before, from a definitive issue with Canadians (!), to an attempt to bring supernatural causes in the story and reveal them as fake by the end of the book, to a collection of implausible and caricaturesque characters surrounded by the usual backcountry morons that would rather fit a Paasilinna novel, and to the incomprehensible intuitions of Inspector Adamsberg. I also went through the sequel to Infomocracy, Null states, albeit this was a real chore as it lacked substance and novelty (the title by itself should have been a warning!).

Watched Night in Paradise (낙원의 밤), another Korean gangster movie, which seems to repeat the trope of bad-guy-on-the-run-meets-lost-girl found in my previously watched Korean Jo-Phil: The Dawning Rage, where the main character, a crooked police officer is radically impacted after failing to save a lost teenager.  (And also in the fascinating The Wild Goose Lake.) The current film is stronger however in creating the bond between the few-words gangster on the run and the reluctant guest Jae-yeon who is on a run of a different magnitude. While the battle scenes are still grand-guignolesque (if very violent) in a Kill Bill spirit, and the gang leaders always caricaturesque, the interplay between the main characters makes Night in Paradise a pretty good film (and explains why it got selected for the Venice Film Festival of 2020). Also went through the appalling Yamakasi by Luc Besson, a macho, demagogical, sexist, simplist, non-story…

## journal of the [second] plague year [deconf’d]

Posted in Books, Kids, Mountains, pictures, Travel, University life, Wines with tags , , , , , , , , , , , , , , , , , , , , , , , , , on May 15, 2021 by xi'an

Read the third volume of Parker’s Engineer Trilogy, The Escapement. Which I found very slow-paced, with loads of mechanistic vocabulary I did not know, and it took me a while to read the book! Still, some sections are definitely worth reading, like the one on Necessary Evil, seen as the tolerance zone between exactitude and error, from and engineer viewpoint… And the final chapters are truly terrific, very dark and pessimistic, keeping me awake till the wee hours. Even though all pieces of the machinery fit too well in the end! But I also reflected on the ambivalent role of the very few women in this third novel, dooming the entire country while remaining stuck in the lover-wife-mother triangle, with no engineering or military role…

“He didn’t for one moment doubt the accuracy of the tables, but how on earth did the book’s author know these things? It could only be that, at some time in the past, so long ago that nobody remembered them any more, there had been sieges of great cities; so frequent and so commonplace that scholarly investigators had been able to collate the data-troop numbers, casualty figures-and work out these ratios, qualified by variables, verified by controls (…) to be inferred from the statistical analyses in a manual of best city-killing practice. Extraordinary thought (…) suppose the book was the only residue left by the death of thousands of cities, each one of them as huge and arrogant in its day as the Perpetual Republic—the Eternal City of this, the Everlasting Kingdom of that, squashed down by time and oblivion into a set of mathematical constants for predicting the deaths of men in battle.”

I also read La Saga des Écrins, by François Labande, in the iconic Guérin series, about the Écrins range in the French Alps, where we spent a fortnight last summer, a rather classical if enjoyable story of the climbers making firsts on the peaks of this “wild” area of the Alps. (As an aside, François Labande started Mountain Wilderness France, whose goal is to keep mountains as a place of wilderness and to clean them from artificial infrastructures.) The cover includes a very nice drawing of La Meige by Jean-Marc Rochette. I also read another delightful short story by P. Djèlí Clark, The Angel of Khan el Khalili. Obviously set in the same fantasy steampunk Cairo of the early 1900’s.

Still turning the crank of the new past machine, I made bigoli, the Venetian equivalent of soba noodles, with both an anchovies sauce and a clam sauce as well (if not from the Laguna!), a rhubarb clafoutis (not yet from our garden), Lebanese humus (without the skin!). Noticed a sharp rise in the price of BrewDog beers, thanks to the new taxes courtesy of Brexit! But still ordered a box of their Nanny State for the summer…

Watched the movie Jo-Phil: The Dawning Rage (!), which makes a great job of setting characters and installing a seedy atmosphere of violence and corruption but completely fails at delivering a convincing story, still gripping enough to watch till the end. And binge-watched a Korean TV series called Signal related to the stunning Memories of Murder (and a collection of real crimes in South Korea from the 1980’s to the last decade). While far from perfect, with a tendency to repeat some scenes twice, the usual theatrics of such series, and the paradoxes of temporal travel (!), the show is nonetheless one of the best Korean dramas I watched… Had  a quick look at the very Netflixy Shadow and Bones. To discover that the trilogy was merged with Six of Crows. Which is strange as the time lines completely differ. But logical if considering that Six of Crows is better written and paced than the earlier trilogy, albeit not outstanding. This is a 12⁺ YA read after all..!

## monomial representations on Netflix

Posted in Books, Kids, pictures, Travel with tags , , , , , , , , , , , , on February 16, 2021 by xi'an

When watching the first episode of Queen’s Gambit, following the recommendations of my son, I glimpsed the cover of a math thesis defended at Cornell by the mother of the main character..! Prior to 1957, year of her death. Searching a wee bit further, I found that there exists an actual thesis with this very title, albeit defended by Stephen Stanley in 1998 at the University of Birmingham. that is, Birmingham, UK [near Coventry]. Apart from this amusing trivia piece, I also enjoyed watching the first episodes of the series, the main actor being really outstanding in her acting, and the plot unfolding rather nicely, except for the chess games that are unrealistically hurried, presumably because watching people thinking is anathema on TV! The representation of misogyny at the time is however most realistic (I presume|!) and definitely shocking. (The first competition game when Beth Hamon loses is somewhat disappointing as failing to predict a Queen exchange is implausible at this level…) However, the growing self-destructive behaviour of Beth made me cringe to the point of stopping the series. The early episodes also reminded me of the days when my son had started playing chess with me, winning on a regular basis, had then joined a Saturday chess nearby, was moved to the adult section within a few weeks, and … stopped altogether a few weeks later as he (mistakenly) thought the older players were making fun of him!!! He never got to any competitive level but still plays on a regular basis and trashes me just as regularly. Coincidence or not, the Guardian has a “scandalous” chess story to relate last week,  when the Dutch champion defeated the world top two players, with one game won by him having prepared the Najdorf Sicilian opening up to the 17th round! (The chess problem below is from the same article but relates to Antonio Medina v Svetozar Gligoric, Palma 1968.)