Archive for Osaka

Insane craving for food

Posted in pictures, Travel, Wines with tags , , , , , , , , , , , , , , , on August 18, 2020 by xi'an

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

Posted in Mountains, pictures, Statistics, Travel with tags , , , , , , , , , , , , on June 4, 2020 by xi'an

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]

Posted in Books, Mountains, Running, Travel with tags , , , , , , , , , , , , on September 8, 2019 by xi'an

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!)


temples on Mount Koya

Posted in Mountains, pictures, Running, Travel with tags , , , , , , , on September 1, 2019 by xi'an

bye and thank you for all the fish!

Posted in pictures, Travel with tags , , , , , , , , , , on August 24, 2019 by xi'an