Archive for Alps

Astrostatistics school

Posted in Mountains, pictures, R, Statistics, Travel, University life with tags , , , , , , , , , , , , , , , , , , , , , on October 17, 2017 by xi'an

What a wonderful week at the Astrostat [Indian] summer school in Autrans! The setting was superb, on the high Vercors plateau overlooking both Grenoble [north] and Valence [west], with the colours of the Fall at their brightest on the foliage of the forests rising on both sides of the valley and a perfect green on the fields at the centre, with sun all along, sharp mornings and warm afternoons worthy of a late Indian summer, too many running trails [turning into X country ski trails in the Winter] to contemplate for a single week [even with three hours of running over two days], many climbing sites on the numerous chalk cliffs all around [but a single afternoon for that, more later in another post!]. And of course a group of participants eager to learn about Bayesian methodology and computational algorithms, from diverse [astronomy, cosmology and more] backgrounds, trainings and countries. I was surprised at the dedication of the participants travelling all the way from Chile, Péru, and Hong Kong for the sole purpose of attending the school. David van Dyk gave the first part of the school on Bayesian concepts and MCMC methods, Roberto Trotta the second part on Bayesian model choice and hierarchical models, and myself a third part on, surprise, surprise!, approximate Bayesian computation. Plus practicals on R.

As it happens Roberto had to cancel his participation and I turned for a session into Christian Roberto, presenting his slides in the most objective possible fashion!, as a significant part covered nested sampling and Savage-Dickey ratios, not exactly my favourites for estimating constants. David joked that he was considering postponing his flight to see me talk about these, but I hope I refrained from engaging into controversy and criticisms… If anything because this was not of interest for the participants. Indeed when I started presenting ABC through what I thought was a pedestrian example, namely Rasmus Baath’s socks, I found that the main concern was not running an MCMC sampler or a substitute ABC algorithm but rather an healthy questioning of the construction of the informative prior in that artificial setting, which made me quite glad I had planned to cover this example rather than an advanced model [as, e.g., one of those covered in the packages abc, abctools, or abcrf]. Because it generated those questions about the prior [why a Negative Binomial? why these hyperparameters? &tc.] and showed how programming ABC turned into a difficult exercise even in this toy setting. And while I wanted to give my usual warning about ABC model choice and argue for random forests as a summary selection tool, I feel I should have focussed instead on another example, as this exercise brings out so clearly the conceptual difficulties with what is taught. Making me quite sorry I had to leave one day earlier. [As did missing an extra run!] Coming back by train through the sunny and grape-covered slopes of Burgundy hills was an extra reward [and no one in the train commented about the local cheese travelling in my bag!]


Autrans, Vercors [jatp]

Posted in Mountains, pictures, Running, Travel with tags , , , , , , , on October 16, 2017 by xi'an

Gorges de la Bourne [jatp]

Posted in Mountains, pictures, Running, Travel with tags , , , , , , , , on October 12, 2017 by xi'an

Rifugio Vittorio Sella al Lauson

Posted in Kids, Mountains, pictures, Travel with tags , , , , , , , , on August 28, 2016 by xi'an

valnontey valleyTo sort of make up for the failed attempt at Monte Rosa, we stayed an extra day and took a hike in Vale d’Aosta, starting from Cogne where we had a summer school a few years ago. And from where we started for another failed attempt at La Grivola. It was a brilliant day and we climbed to the Rifugio Vittorio Stella (2588m) [along with many many other hikers], then lost the crowds to the Colle della Rossa (3195m), which meant a 1700m easy climb. By the end of the valley, we came across steinbocks (aka bouquetins, stambecchi) resting in the sun by a creek and unfazed by our cameras. (Abele Blanc told us later that they are usually staying there, licking whatever salt they can find on the stones.)

steinbocks near Colle della Rossa, Aosta, Jul 16, 2016 near Rifugio Vittorio Stella, Aosta, Jul 16, 2016

The final climb to the pass was a bit steeper but enormously rewarding, with views of the Western Swiss Alps in full glory (Matterhorn, Combin, Breithorn) and all to ourselves. From there it was a downhill hike all the way back to our car in Cogne, 1700m, with no technical difficulty once we had crossed the few hundred meters of residual snow. And with the added reward of seeing several herds of the shy chamois mountain goat.

end of the plateau, Rifugio Vittorio Stella, Aosta, July 16, 2016Except that my daughter’s rental mountaineering shoes started to make themselves heard and that she could barely walk downwards. (She eventually lost her big toe nails!) It thus took us forever to get down (despite me running to the car and back to get lighter shoes) and we came to the car at 8:30, too late to contemplate a drive back to Paris.

view from Colle Della Rossa, Aosta, July 16, 2016

on Monte Rosa [a failed attempt at speed climbing]

Posted in Kids, Mountains, pictures, Running, Travel with tags , , , , , , , , , , , on July 24, 2016 by xi'an

With my daughter Rachel and her friend Clément, we tried last week to bag a few summits in the Monte Rosa massif, which stands between Italy (Aosta) and Switzerland (Zermatt). I wanted to take advantage of the Bastille Day break and we drove from Paris to Aosta in the very early morning, stopping in Chamonix to rent shoes and crampons, and meeting with our guide Abele Blanc at noon, before going together to the hut Rifugio Città di Mantova. At 3500m. Our goal was to spent the night there and climb to Punta Gnifetti (Rifugio Margherita) and Zumstein the next morning. Before heading back to Paris in the evening. However, it did not work out that way as I got a slight bout of mountain sickness that left me migrainous, nauseous, and having a pretty bad night, despite great conditions at the hut… So (despite my intense training of the previous weeks!) I did not feel that great when we left the hut at 5am. The weather was fine if cold and windy, but after two hours of moderate climbing in a fairly pleasant crispy snow of a glacier, Rachel was too out of breath to continue and Abele realised my nose had [truly] frozen (I could not feel anything!) and took us down before continuing with Clément to both peaks. This was quite a disappointment as we had planned this trip over several months, but it was clearly for the best as my fingers were definitely close to frozen (with my worst case ever of screamin’ barfies on the way down!). And we thus spent the rest of the morning waiting for our friends, warming up with tea in the sunshine. Upon reflection, planning one extra day of acclimatisation to altitude and cold would have been more reasonable and keeping handwarmers in our backpacks as well… In any case, Clément made it to the top with Abele and we got a good altitude training for the incoming San Francisco half-marathon. Plus an epic hike the next day around Cogne.

sunset over Rifugio Città di Mantova

Posted in Kids, Mountains, pictures, Travel with tags , , , , , , on July 22, 2016 by xi'an

up to Rifugio Città di Mantova

Posted in Kids, Mountains, pictures, Running, Travel with tags , , , , , , , , , on July 20, 2016 by xi'an