Archive for the Mountains Category

better together?

Posted in Mountains, Statistics, University life, Books, pictures with tags , , , , , , , , on August 31, 2017 by xi'an

Yesterday came out on arXiv a joint paper by Pierre Jacob, Lawrence Murray, Chris Holmes and myself, Better together? Statistical learning in models made of modules, paper that was conceived during the MCMski meeting in Chamonix, 2014! Indeed it is mostly due to Martyn Plummer‘s talk at this meeting about the cut issue that we started to work on this topic at the fringes of the [standard] Bayesian world. Fringes because a standard Bayesian approach to the problem would always lead to use the entire dataset and the entire model to infer about a parameter of interest. [Disclaimer: the use of the very slogan of the anti-secessionists during the Scottish Independence Referendum of 2014 in our title is by no means a measure of support of their position!] Comments and suggested applications most welcomed!

The setting of the paper is inspired by realistic situations where a model is made of several modules, connected within a graphical model that represents the statistical dependencies, each relating to a specific data modality. In a standard Bayesian analysis, given data, a conventional statistical update then allows for coherent uncertainty quantification and information propagation through and across the modules. However, misspecification of or even massive uncertainty about any module in the graph can contaminate the estimate and update of parameters of other modules, often in unpredictable ways. Particularly so when certain modules are trusted more than others. Hence the appearance of cut models, where practitioners  prefer skipping the full model and limit the information propagation between these modules, for example by restricting propagation to only one direction along the edges of the graph. (Which is sometimes represented as a diode on the edge.) The paper investigates in which situations and under which formalism such modular approaches can outperform the full model approach in misspecified settings. By developing the appropriate decision-theoretic framework. Meaning we can choose between [several] modular and full-model approaches.


Posted in Mountains, pictures, Travel, Wines with tags , , , , , on August 20, 2017 by xi'an

Il cimitero degli alpinisti

Posted in Mountains, pictures, Travel with tags , , , , , , , , on August 20, 2017 by xi'an

In the cemetery around Chiesa Vecchia in Macugnaga, at the bottom of Monte Rosa (and the other size from Zermatt), there is such a number of alpinists and guides buried there that the cemetery is called the cemetery of the alpinists. A memorial recalls deaths of local guides and climbers on the different routes of the Monte Rosa group [there is no Monte Rosa peak per se but a collection of 15 tops above 4000m]. Plus crosses and plaques on the church wall for those whose bodies were not recovered, according to a local guide. (Which sounds strange given that these are not the Himalayas! Unless these are glacier-related deaths…]

maggiore alba [jatp]

Posted in Mountains, pictures, Running, Travel with tags , , , , , , on August 17, 2017 by xi'an

at the foot of Monte Rosa

Posted in Mountains, pictures, Travel, Wines with tags , , , , , , , , , on August 16, 2017 by xi'an

After last-year failed attempt at climbing a summit in the Monte Rosa group, we came back for hiking on the “other side” of Monte Rosa, at the Italian foot of Dufourspitze with less ambitious plans of hiking around this fantastic range. Alas the weather got set against us and thunderstorms followed one another, making altitude hikes unreasonable because of the fresh snow and frequent fog, and lower altitude walks definitely unpleasant, turning the trails into creeks.

While we had many nice chats with local people in a mixture of French and Italian, and sampled local cheese and beers, this still felt like a bit of a wasted vacations week, especially when remembering how reasonable the weather had been the week before in Scotland. However, all things considered, the previous week had seen a deadly heat wave cross the south of Europe that very week, so I should not be complaining about rain and snow! And running a whole week checking the altimeter instead of the chronometer is a nice experience.

In Dunvegan Castle gardens [jatp]

Posted in Mountains, pictures, Travel with tags , , , , , , on August 15, 2017 by xi'an

paradise island

Posted in Mountains, pictures, Travel with tags , , , , , , , on August 14, 2017 by xi'an

As should be obvious from the pictures posted here in the past days, I have been away on vacations on the Scottish island of Skye, part of the Inner Hebrides. This is a place that had stood very high in my dream vacation places, mostly because of the mountain range that stands at the bottom of the island, called the Cuillins. There are 13 Munroes (tops above 3,000 feet) in that range and its entire traverse takes a very long day, including several belays. As I was there for a family vacation, we [alas!] only went up the easiest group, made of Sgùrr nan Gillean, Am Basteir, and Bruach na Frìthe, and did not climb Sgùrr nan Gillean. This was a fairly easy hike with a 900m differential, the only difficulty being in route finding. Which was made harder than needed by me first confusing a group of three hills with these Cuillins for the first third of the hike! And relating to instructions in our guidebook that covered the opposite side of the mountains. It was however a most pleasant walk, quite dry by Scottish standards (where it is often hard to separate water and soil) and with sun part of the way (it actually did not start to rain until the final half-hour). And not too many people on the path.
The other days saw easier walks at lower elevations, from a grassy and pleasant route to the top of MacLeod’s North Table [with terrific views of Western Skye and the Outer Hebrides], to a tour of the Gresornish peninsula under a pouring rain but with an amazing light (and an exciting crossing of a definitely web bog where even sheep did not do]. Overall, this was a great week in a secluded location, keeping mostly away from the few tourist traps [except for a trip to the Isle of Skye Brewery and to the compulsory Neist Point lighthouse] and I hope I can get back there one day. Although other Northern paradise islands like Mull, Harris, and the Faeroe are also beguiling..!
An unsolved puzzle about this visit to Skye is that, while there are sheep all over the island, which makes spotting any form of wildlife but midges impossible!, lamb meat is curiously absent from restaurant menus [except from the offal parts used in haggis]. The few persons we asked seemed perplexed by our question and had no convincing explanation to this absence!