Archive for plague

La peste et la vigne [book review]

Posted in Books, Kids, Travel with tags , , , , , , , on March 17, 2019 by xi'an

During my trip to Cambodia, I read the second volume of this fantasy cycle in French. Which I liked almost as much as the first volume since the author continues to explore the mystery of the central character Syffe and its relations with some magical forces at play in his universe. As in most stories uniquely centred on a single character point of view the recurring ponderings of Syffe about his role in life, the existence of supernatural forces, and his own sanity may tend to get annoying at time. But the escape from the mines and the subsequent stay in a mountain kingdom are well-paced, especially the description of the plague that allows such an escape. The last section is more connected with the first volume and sees more warfare, again with sudden reversals of fortune (no further spoiler!). The final chapters see a lot explained about many aspects of the story and the raison d’être of the character, even though the very last surprise is somewhat predictable. But opening new vistas for the future volumes. There are still many threads I could have pulled to point some potential influences of earlier cycles, from Stephen Donaldson’s Thomas Covenant chronicles, which I simply hated!, to Robin Hobb’s Soldier’s son. Since both stories convey the feeling of a magical force at the level of the whole land (or universe), with the unprepared and imperfect “hero” able to impact this land in dramatic ways. And again Elizabeth Moon’s Deeds of Paksenarion for the depiction of mercenary companies…

pictures at an exhibition

Posted in Kids, pictures, Travel with tags , , , , , , , on November 25, 2017 by xi'an

Last weekend we went to a local cultural centre to check on the exhibit of pictures from Madagascar our daughter and her friends had set to a month, following their humanitarian trip there last summer that was supported in part by the town council. While we had already seem these pictures, it was nice to see them in perspective. Hopefully inducing more volunteers to spend time in this particularly poor country, facing a silent humanitarian crisis. Including numerous cases of pneumonic plague… Donations can be made to MadaClinics, the NGO supporting medical rural centres. (USAid also has a program specifically aimed at Madagascar.)

Sequentially Constrained Monte Carlo

Posted in Books, Mountains, pictures, Statistics, University life with tags , , , , , , , , , , on November 7, 2014 by xi'an

This newly arXived paper by S. Golchi and D. Campbell from Vancouver (hence the above picture) considers the (quite) interesting problem of simulating from a target distribution defined by a constraint. This is a question that have bothered me for a long while as I could not come up with a satisfactory solution all those years… Namely, when considering a hard constraint on a density, how can we find a sequence of targets that end up with the restricted density? This is of course connected with the zero measure case posted a few months ago. For instance, how do we efficiently simulate a sample from a Student’s t distribution with a fixed sample mean and a fixed sample variance?

“The key component of SMC is the filtering sequence of distributions through which the particles evolve towards the target distribution.” (p.3)

This is indeed the main issue! The paper considers using a sequence of intermediate targets hardening progressively the constraint(s), along with an SMC sampler, but this recommendation remains rather vague and hence I am at loss as to how to make it work when the exact constraint implies a change of measure. The first example is monotone regression where y has mean f(x) and f is monotone. (Everything is unidimensional here.) The sequence is then defined by adding a multiplicative term that is a function of ∂f/∂x, for instance

Φ(τ∂f/∂x),

with τ growing to infinity to make the constraint moving from soft to hard. An interesting introduction, even though the hard constraint does not imply a change of parameter space or of measure. The second example is about estimating the parameters of an ODE, with the constraint being the ODE being satisfied exactly. Again, not exactly what I was looking for. But with an exotic application to deaths from the 1666 Black (Death) plague.

And then the third example is about ABC and the choice of summary statistics! The sequence of constraints is designed to keep observed and simulated summary statistics close enough when the dimension of those summaries increases, which means they are considered simultaneously rather than jointly. (In the sense of Ratmann et al., 2009. That is, with a multidimensional distance.) The model used for the application of the SMC is the dynamic model of Wood (2010, Nature). The outcome of this specific implementation is not that clear compared with alternatives… And again sadly does not deal with the/my zero measure issue.

Company of Liars

Posted in Books with tags , , on May 11, 2009 by xi'an

This weekend was another long weekend (for Friday was also a bank holiday) and so I took the opportunity to read a book brought back from my last trip to England, Company of Liars, bought mostly because it was on sale at the Kensington Waterstone’s (and also because Susanna Gregory’s Matthew Bartholomew novels made me like this incredible period of England’s history). The overall plot is not that new: like Chaucer’s Canterbury Tales, it consists in bringing together nine unlikely travel companions and to slowly uncover the secret story of each of those travellers. As indicated by the subtitle, a novel of the plague, an additional element in the plot is that this group is fleeing the propagation of the bubonic plague of 1348 across England. They somehow manage to avoid catching the Black Death but most of them end up dead by other means, always a consequence of their major lie (since all are indeed liars). Even though the story is told by one of the characters, a trader in holy relics, there is no main character in this book and, in this respect, it is quite different from Gregory’s novels.

After finishing the book, I cannot really say if I enjoyed it that much. The style is rather heavy, the link with historical accuracy dubious, and the fantastic element fairly thin. The story is definitely gloomy and the attempts at literary inventions short-fused. As put by an earlier review in The Scotsman, it is easy “to dismiss Company of Liars as pedestrian”… At the same time, the Chauncerian stories that come with each traveller are quite engrossing and the unraveling of the societal structures brought by the plague convincing, including the major move “back” in religious practices. While I would certainly not go as far as The New York Times and call the book “a jewel of a medieval mystery”, it makes for a nice weekend read and nothing more.