a journal of the plague year³ [beginning of the end?]

Made my first trip to Warwick this year despite the travel restrictions imposed by the omnipresent Omicron version. My flights got repeatedly cancelled, meaning I had to fly through Schipol (thanks for the Gouda cumin cheese and stroopwafelen!) and leave at more-than-early hours (even by my standards!). But had more conversations than usual, plus delivered my lecture masked-face-to-masked-face to 19 Warwick students, the first time in 709 days!

Read [in French] the two BDs of Milo Manara on Michelangelo [Merisi or Amerighi da] Caravaggio, which was a Xmas gift!, with as always great in the large scale and character drawings, if not Caravaggio’s chiaroscuro, but less in the scenario, esp. the second part and even more esp. given the agitated life of the artist. And another BD taking place in Cayenne, in 1742, whose drawings also appear in local guides.

Watched 14 Peaks: Nothing is impossible on Netflix, following Nepalese mountaineer Nirmal Purja [of Everest jam fame!] and his team as they manage to climb all 14 eight thousander peaks over 6 months. Including Shishapangma in Tibet, with the added hardship to procure a climbing permit from Chinese authorities for that mountain. The documentary focuses a wee bit too much on Purja’s persona and not enough on the team of sherpas and on the climb itself. Except for the summitings there is very little about the technical difficulties of each summit and the hardships and failed attempts. For instance, the amazing feat of first installing fixed ropes for all 14 summits is only alluded to. Despite reservations about the use of supplementary oxygen (without which, as stressed by Messner, the attempt of climbing all 8000ers in one season would have proved truly impossible and suicidal) and heliporting from one base camp to another, the enormity of the achievement of this team of sherpas remains a monument in the climbing world. (Even only considering that Everest, Lhotse and Makalu were climbed in two days total!)

Siem Reap conference

As I returned from the conference in Siem Reap. on a flight avoiding India and Pakistan and their [brittle and bristling!] boundary on the way back, instead flying far far north, near Arkhangelsk (but with nothing to show for it, as the flight back was fully in the dark), I reflected how enjoyable this conference had been, within a highly friendly atmosphere, meeting again with many old friends (some met prior to the creation of CREST) and new ones, a pleasure not hindered by the fabulous location near Angkor of course. (The above picture is the “last hour” group picture, missing a major part of the participants, already gone!)

Among the many talks, Stéphane Shao gave a great presentation on a paper [to appear in JASA] jointly written with Pierre Jacob, Jie Ding, and Vahid Tarokh on the Hyvärinen score and its use for Bayesian model choice, with a highly intuitive representation of this divergence function (which I first met in Padua when Phil Dawid gave a talk on this approach to Bayesian model comparison). Which is based on the use of a divergence function based on the squared error difference between the gradients of the true log-score and of the model log-score functions. Providing an alternative to the Bayes factor that can be shown to be consistent, even for some non-iid data, with some gains in the experiments represented by the above graph.

Arnak Dalalyan (CREST) presented a paper written with Lionel Riou-Durand on the convergence of non-Metropolised Langevin Monte Carlo methods, with a new discretization which leads to a substantial improvement of the upper bound on the sampling error rate measured in Wasserstein distance. Moving from p/ε to √p/√ε in the requested number of steps when p is the dimension and ε the target precision, for smooth and strongly log-concave targets.

This post gives me the opportunity to advertise for the NGO Sala Baï hostelry school, which the whole conference visited for lunch and which trains youths from underprivileged backgrounds towards jobs in hostelery, supported by donations, companies (like Krama Krama), or visiting the Sala Baï  restaurant and/or hotel while in Siem Reap.