journal of the [second] plague year [con’d]

Read The Office of Gardens and Ponds (in French), by Didier Decoin [whom John l’Enfer I read more than forty years ago, with no lasting memories!], another random book found in the exchange section of our library!  While a pastiche of Japanese travel novels, the book is quite enjoyable and reminded me of our hike on the Kumano Kodō routes, two years ago. The tale takes place in 12th Century Japan and tells of the epic travel of a widow to the capital, Kyoto, carrying live carps for the gardens of the emperor. While some sections are somewhat encyclopedic on the culture of medieval Japan [and I thus wonder how Japanese readers have reacted to this pastiche], the scenario is rather subtle and the characters have depth, incl. the dead husband. The scene of the perfume competition is particularly well-imagined and worth reading on its own. I figure I will not bring the book back. (Warning: this book was voted a 2019 winner of the Bad Sex Award!). Also read Patti Smith’s Devotion, which was one of my Xmas presents. I had never read anything but Smith’s songs, since 1976 (!) with Horses, missing by little some of her concerts as on the week I was in Rimini… The book is quite light, and not only length-wise, made of two travel diaries in (to?) Paris and in (to?) Southern France, where she visits Camus’ house, and of a short story she writes on the train. While the diaries are mildly interesting, if a bit American-Tourist-in-Paris-cliché (like this insistence to find glamour in having breakfast at Café Flore!), the story comes as a disappointment, both for being unrealistic [in the negative sense] and for reproducing the old trope of the young orphan girl becoming the mistress of a much older man [to continue skating]. The connection with Estonia reminded me of Purge, by Sofi Oksanen, a powerful novel about the occupations of Estonia by Nazis and Soviet troups, an haunting novel of a different magnitude…

Made  soba noodles with the machine, resulting into shorte-than-life noodles, due to the high percentage of buckwheat flour in the dough, still quite enjoyable in a cold salad. Also cooked a roghan josh lamb shack, along with chapatis flavoured with radish leaves [no fire alarm this time] and a vegetable dahl whose recipe I found in Le Monde the same morn. Also took advantage of the few weeks with fresh and tender asparagus sold at the local market to make salads.

Watched a few episodes of Better than Us, Лучше (чем люди), a Russian science-fiction series set in a close future with humanoid robots replacing menial workers, until one rogue version turns uncontrollable, à la Blade Runner. There are appealing aspects to the story, besides the peep into a Russian series and the pleasure of listening to Russian, about the porous frontier between human and artificial intelligence. The scenario however quickly turns into a predictable loop and I eventually lost interest. Even faster did that happen with the Irregulars of Baker Street horror series, which I simply could not stand any further (and which connection with Holmes and Watson is most tenuous).

Having registered for a vaccination to the local pharmacy, I most got surprisingly called a few days later mid-afternoon to come at once for a shot of AstraZeneca, as they had a leftover dose. And a rising share of reluctant candidates for the vaccine!, despite David’s reassurances. I am unsure this shot was done early enough to get abroad for conferences or vacations in July, but it is one thing done anyway. With no side effect so far.

non-reversible guided Metropolis–Hastings

Kengo Kamatani and Xiaolin Song, whom I visited in Osaka last summer in what seems like another reality!, just arXived another paper on a non-reversible Metropolis version. That exploits a group action and the associated Haar measure.

Following a proposal of Gustafson (1998), a ∆-guided Metropolis–Hastings kernel is based on a statistic ∆ that is totally ordered and determine the acceptance of a proposed value y~Q(x,.) by adding a direction (-,+) to the state space and moving from x if ∆x≤∆y in the positive direction and if ∆y≤∆x in the negative direction [with the standard Metropolis–Hastings acceptance probability]. The sign of the direction switches in case of a rejection. And the statistic ∆ is such that the proposal kernel Q(x,.) is unbiased, i.e., agnostic to the sign, i.e., it gives the same probability to ∆x≤∆y and ∆y≤∆x. This modification reduces the asymptotic variance compared with the original Metropolis–Hastings kernel.

To construct a random walk proposal that is unbiased, the authors assume that the ∆ transform takes values in a topological group, G, with Q further being invariant under the group actions. This can be constructed from a standard proposal by averaging the transforms of Q under all elements of the group over the associated right Haar measure. (Which I thought implied that the group is compact, except I forgot to account for the data update into a posterior..!) The worked-out example is based on a multivariate autoregressive kernel with ∆x being a rescaled non-central chi-squared variate. In dimension 24. The results show a clear improvement in effective sample size per second evaluation over off-the-shelf random walk and Hamiltonian Monte Carlo versions.

Seeing the Haar measure appearing in the setting of Markov chain Monte Carlo is fun!, as my last brush with it was not algorithmic. I would think the proposal only applies to settings where the components of the simulated vector are somewhat homogeneous in that the determinationthe determination of both the group action and a guiding statistic seem harder in cases where these components take different meaning (or live in a weird topology). I also lazily wonder if selecting the guiding statistic as a gradient of the log-target would have any interest.

夢幻花 [Dream flower]

Another Japanese mystery novel by Higashino Keigo, which I read in French under the title La fleur de l´illusion [on a sunny Sunday afternoon, under my fig tree] and enjoyed both for its original, convoluted (and mostly convincing) plot and for the well-rendered interaction between the young protagonists. And also for having a few connections with my recent trip, from one protagonist studying nuclear physics at the University of Osaka to a visit to the back country of Katsuura. (The author himself graduated from Osaka Prefecture University with a Bachelor of Engineering degree.) Spoiler warning: the only annoying part of the plot was the resolution of the mystery via a secret society run by a few families of civil servants, which as always sounds to me like a rather cheap way out. But not enough to ruin the entire novel.

 

Japanese mushrooms [jatp]

the three Kumano shrines [jatp]