a journal of the plague year² [closing again]

Had to cancel my third and final trip to Warwick this year as the Omicron scare had countries locking their borders (too late, most likely), meaning the UK was reinstating on entering travelers a self-seclusion period until the test results were known. Despite getting my third shot in time (with no side-effect whatsoever). And France retaliated in imposing PCR tests as well…

Read (over the Atlantic) an older novel of William Gibson, The Peripheral. Which is a rather standard cyberpunk Gibson with lots of (2021’s) brand names (at least at the beginning), a messy build-up of the (dual) universe, plenty of gadgets, a long-going form of fascination for super-lethal weapons and militarised survivalists, followed by a vague explanation of the temporal paradox of conversing with the future/past, and a rather lame closure with a shoot shoot bang bang resolution and some people getting absurdly rich… I am unsure I will get through the second novel, The Agency, which I bought at the same time, unless we manage to fly to French Guiana on Xmas day. Even though The Guardian is quite excited about it.

Watched Kan Eguchi’s The Fable after coming back from Mexico (not on the plane, when I slept most of the flight), which is cartoonesquely funny, except for lengthy fighting scenes. As it should, since directly inspired from a manga. While I missed the jokes about Osaka’s special dialect and food, it was absurdly funny! And fit for a particularly rainy weekend. The second installment, which I watched later, is darker and more disturbing…

a journal of the plague year² [600+]

Returned to Warwick for the first time in 600 days!, most pleasantly reconnecting with my colleagues there and realising some were almost as freshly back to the department as myself. But also noticed a strong difference with France in terms of wearing mask and practicing social distanciation among the students (at the University) and the general population (in the local Tesco or the train to the airport). Which may explain for the persistently high number of contaminations, when compared with neighbouring countries. Despite its high vaccination rate.

Read the second volume of Baru Cormorant, after enjoying so much the first instalment (under the Corsican relentless sun). However, it was such a disappointment, as it seemed written by a completely different author, including the style, with the story being more broken, more difficult to follow, and the characters becoming shallow and uninteresting. This is particularly true of Baru, who sent from a sharp focus on her goal in Traitor, to a purposeless floatsam in Monster. With a highly artificial rescue of her ethics in [warning, spoiler ahead!] killing her lover Tain Hu (and hundreds of others) in the first volume. I currently doubt I will buy the third one… A stormy night kept me awake and as a result help me finish the last hundred pages!

Watched Mute, dubbed a “Netflix disaster” in The Guardian! (and following the appalling Warcraft!). Which postulate of a mute character could have been rewarding, had not the characters be of cardboard consistency. And the plot so transparent most of the scenes had to be shot at night. And the cheap plagiarism of Blade Runner is simply ludicrous. I also watched Bong Joon-Ho’s Okja, a satire about the meat industry producing hippo-like pigs that I found very heavy-handed, especially in its characters.Started cooking bread on a regular basis once again, as weather is turning colder and baking also warms up our drafty kitchen! Now turning to a heavier type of loaf, mixed wheat and rye, and reducing the amount of water to make it last longer. And also made a first attempt at Okonomyaki, this tortilla-like dish made of shredded cabbage and flour that I enjoyed very much in Osaka. The result was pleasant enough but very, very far from the original, maybe due to my using (soba) buckwheat rather than plain flour. Or using regular stock rather than daishi stock.

Insane craving for food

Within a couple of weeks, I read two related US stories about ordering food from an insanely far destination, like hand-made frozen pizza from Napoli, Italia, or like one startup called Goldbelly ships frozen food made by some restaurants nationwide. (With a motto of Whatever [food] they dream of, wherever they are.) While I am not consistent in consuming non-local food and drinks, like my mass orderings of Italian wines and Darjeeling teas, and while I’d love to get a new taste of Toukoul’s Ethiopian dishes, a creamy sepia risotto from Da Franz, an okonomiyaki from any street stall in Osaka, and many many other dishes from all over the World, it sounds to me rather debatable to have a special single meal prepared on the other side of the World and delivered immediately to one’s table… Furthermore, one of the perks of dining at fine restaurants is exactly to dine at fine restaurants, not in one’s own room, and having starred chefs’ dishes ending up in reheated frozen plastic containers is certainly killing a major share of the experience.

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.

Japan’s Kumano Kodo pilgrimage [book review]

When preparing our hiking trip to the Kumano Kodo pilgrimage route, I was extremely pleased to find a dedicated guidebook that covered precisely the region we wanted to explore and provided enough background material to make the walk sound feasible. However, once I found the Kumano Travel reservation website, run most efficiently by the Tanabe City Kumano Tourism Bureau, the information contained in this site made the guidebook less relevant. And when we arrived in Tanabe at the start of the trail, I found that the Bureau was also distributing free leaflets in English for each of the three main routes, which described day-by-day the stages of the hikes, as well as recommendations and tips. Making in the end or a posteriori the guidebook superfluous. (As the detailed description of the routes was not necessary, given how clearly they are identified. The leaflet managed to stand the five days on the trail despite rain, humidity, frequent consultations and a general lack of care, as shown above!)  Hence, while there is nothing wrong with the guidebook which also includes an extra day-hike along the Eastern coast of the Kii peninsula and another one from Koyasan to the bottom of the cablecar [again covered by leaflets at the local tourism bureau], I would not strongly recommend it. Interestingly (?), when I stated these mere facts as a review on Amazon, I was rejected as contravening their review guidelines without further precision… (I can only post comments on the French portal of Amazon as my associate gains mean that I never “buy” anything on the US portal!)