## a journal of the plague year [grey & dry ‘nuary reviews]

Posted in Books, Kids, pictures, Travel with tags , , , , , , , , , , , , , , , , , , , , , , , , , , on February 27, 2021 by xi'an

Read a Danish novel Ø by Siri Ranva Hjelm Jacobsen, directly translated as island in other languages (incl. French), which was a b’day gift from my wife, a book about the longing of uprooted Faroeses for their island,  rather than about the mathematical meaning of the empty set!, and the connection between a young third generation young woman and her grand-mother’s story. Very well written, with a side entry on Faroese recent history, incl. the British occupation during WWII, just before they invaded Iceland. (And feeding my hopes to visit the Faroe in a near and brighter future!)

Cooked more (Flemmish) red and (curried) white cabbage. Moved to baking spelt bread with spelt yeast as it takes less than ten minutes of actual work!  Attempted an Ethiopian meal with key wat (beef) stew,  a vegetable version, and injera (pancakes) when I realised the teff cereal could be replaced with buckwheat, a basic staple in Breton households! But the injera tasted and looked more like a galette, so this was not the real thing… Nonetheless a nice family meal.Watched the second instalment of The Hundred-Year-Old Man Who Climbed Out of the Window and Disappeared, The 101-Year-Old Man Who Skipped Out on the Bill and Disappeared, which is the straight continuation of the former if not as funny. (And not directly linked to the books.)

Read Time of Contempt, second volume in the Witcher’s novels. Not particularly impressive, with a lot of infodump chitchat, an almost absent Yennefer, a (thankfully short-lived) threat of the return of the magicians’ boarding school!, a gratuitous (?) visit by the Wild Hunt myth, some Star War inspired monster, an incomprehensible and highly predictable coup on the magicians’ council, and a teenage gang (in a Mark Lawrence rewriting Lord of the Flies spirit!), an inexplicable collapse of the balance of powers between the kingdoms. And I found the rendering of the rape scene at the end of the book most disturbing…

## a journal of the plague year [long weekend reviews]

Posted in Books, Kids, pictures with tags , , , , , , , , , , , , , , , , , , , , , , , on August 15, 2020 by xi'an

Read Thinblade, ordered by mistake as I confused the author David Wells for another more famous one! An absolute disaster, from the poor quality of the printed-on-order self-published amazon-made copy to the abyssal style of the author (or of his dog). The story has no depth and no originality [a teenager discovers he must save the World against an evil entity released from captivity and gathers a team of un.be.lie.va.ble followers], the characters are uni-dimensional, either unbelievably good or complete evil and a colour comes with them to tell the hero which is which. The style (or lack thereof!) is massively indigest, with numerous repetitions about the feelings and questionings of the central characters, plus an hilarious focus on food, all menus being included in the text!, same endless drones about the incredible beauty of the visited castles a few days of ride from the hero’s farm. The plot is, again, laughably simplistic, making the Shannara books I read a few months ago sounding like an elaborate literary construct, and completely predictable. I cannot imagine myself or anyone else’s dog reading further books in the series

Watched The Old Guard after an exhausting day, including a (physical) trip to a dreaded DIY store!, after reading a somewhat lukewarm review in The New Yorker… I found out later that the film is based on a comics series with the same title. And it shows from the lack of real plot (need to get quickly to Afghanistan? just drop out from a freight train in the middle of Sudan…) to the predictability of the story (set-up heroes fight bad guys and at the end, guess what, …), to the massive amount of stale gun fights with the addition of archaic weapons (to make sure everyone understands the old guard is really old!). The funniest part is actually taking place in Goussainville, France, in the ghost section of this town located on the path of De Gaulle airport planes (and thus evacuated, but not demolished), and in its Roman church (listed, hence intact!). The lack of moral imperative or of higher being driving such immortal killers, who mostly seem tired of said immortality, and the absence of connection with the locals (as e.g. in the scenes taking place in Morocco) do not make this B movie any better. (And the French character definitely has an English accent!)

Had a chance lunch in a Michelin recommended restaurant, on the road to Chenonceau and a family vacation, as we were looking for an open restaurant. The haddock appetizer was fantastic (and enough!), while the trout was not so great, presumably frozen, even though the vegetables were original (incl. chayotte) and yummy.

Read Konungsbók (The King’s Book) by Arnaldur Indriðason, found on my mother’s bookshelves, which is a stand-alone book more of the “involuntary spy” type found in Eric Ambler‘s stories than the usual social theme detective story favoured by Indriðason. While the two involuntary spies in the story are indeed two archeolinguists blundering their way through implausible situations, against hidding Nazis and East German police, as Ambler’s The Dark Frontier, the appeal of the book is in the quest for the ultimate Icelandic saga that would close the nation’s history, The King’s Book, towards recovering other foundational and historical documents hoarded by Denmark. At some point, Halldór Guðjónsson Laxness gets the Nobel Prize in Literature, which first stuns the characters into stupefied pride and second helps them into making another unlikely escape. What I enjoyed in the novel is the feeling of ultimate importance attached to the sagas and their role in cementing Iceland as a genuine nation (again connecting with Laxness, whose books described the social desagregation produced by the American occupation).

## Gibbs for kidds

Posted in Books, Kids, Statistics, University life with tags , , , , , , , , , , , , , , , on February 12, 2018 by xi'an

A chance (?) question on X validated brought me to re-read Gibbs for Kids, 25 years after it was written (by my close friends George and Ed). The originator of the question had difficulties with the implementation, apparently missing the cyclic pattern of the sampler, as in equations (2.3) and (2.4), and with the convergence, which is only processed for a finite support in the American Statistician paper. The paper [which did not appear in American Statistician under this title!, but inspired an animal bredeer, Dan Gianola, to write a “Gibbs for pigs” presentation in 1993 at the 44th Annual Meeting of the European Association for Animal Production, Aarhus, Denmark!!!] most appropriately only contains toy examples since those can be processed and compared to know stationary measures. This is for instance the case for the auto-exponential model

$f(x,y) \propto exp(-xy)$

which is only defined as a probability density for a compact support. (The paper does not identify the model as a special case of auto-exponential model, which apparently made the originator of the model, Julian Besag in 1974, unhappy, as George and I found out when visiting Bath, where Julian was spending the final year of his life, many years later.) I use the limiting case all the time in class to point out that a Gibbs sampler can be devised and operate without a stationary probability distribution. However, being picky!, I would like to point out that, contrary, to a comment made in the paper, the Gibbs sampler does not “fail” but on the contrary still “converges” in this case, in the sense that a conditional ergodic theorem applies, i.e., the ratio of the frequencies of visits to two sets A and B with finite measure do converge to the ratio of these measures. For instance, running the Gibbs sampler 10⁶ steps and ckecking for the relative frequencies of x’s in (1,2) and (1,3) gives 0.685, versus log(2)/log(3)=0.63, since 1/x is the stationary measure. One important and influential feature of the paper is to stress that proper conditionals do not imply proper joints. George would work much further on that topic, in particular with his PhD student at the time, my friend Jim Hobert.

With regard to the convergence issue, Gibbs for Kids points out to Schervish and Carlin (1990), which came quite early when considering Gelfand and Smith published their initial paper the very same year, but which also adopts a functional approach to convergence, along the paper’s fixed point perspective, somehow complicating the matter. Later papers by Tierney (1994), Besag (1995), and Mengersen and Tweedie (1996) considerably simplified the answer, which is that irreducibility is a necessary and sufficient condition for convergence. (Incidentally, the reference list includes a technical report of mine’s on latent variable model MCMC implementation that never got published.)

## the incomprehensible challenge of poker

Posted in Statistics with tags , , , , , , , , on April 6, 2017 by xi'an

When reading in Nature about two deep learning algorithms winning at a version of poker within a few weeks of difference, I came back to my “usual” wonder about poker, as I cannot understand it as a game. (Although I can see the point, albeit dubious, in playing to win money.) And [definitely] correlatively do not understand the difficulty in building an AI that plays the game. [I know, I know nothing!]

## Postdoc in Denmark

Posted in Statistics, University life with tags , , on November 9, 2009 by xi'an

I just received the following email for a two year postodc offer in Lyngby, Denmark:

The Technical University of Denmark (DTU) has a dynamic and active group in Statistics, with a number of researchers concentrating on probabilistic forecasting and renewable energy applications. Focus is given to applied research, but also to new methodological developments. Owing to interesting recent results on spatio-temporal modeling of forecast error fields, we have decided to open a post-doc position for a duration of 2 years, which will mainly relate to that area of  research.