not summiting Volcan Osorno

While in Puerto Varas for BNP13, I tried to summit the nearby Orsono volcano (2652m) but it did not work out… Indeed, Huella Andina, the guiding company, chose to postpone the climb by two consecutive days for fear of snowfall (which did not materialise) and ended up choosing the windiest day of the week. In the meanwhile, Zhu Yichen had joined me and we all three were at the start of the trail (at about 1000m) at the earliest, starting hiking by 4:30 under a magnificent Southern night sky on top of us, with a rich Milky Way. And the Southern X. Obviously all by ourselves. The wind was strong then but quite bearable and the trail of powdery ash quite smooth till we reached a small hut to put crampons and add one more layer, around 1600m.

When we started again the wind had strengthened with the incoming dawn, rising to a point where we could hardly stand up to it, and our guide eventually decided to turn back, as it was only to get worse in the remaining 600m to the top, confirming the earlier prediction of 70km/hour winds… Yichin was of the same opinion and hence we reluctantly turned back down to the bottom of the slope, with the wind mostly on our back and a pleasant steady gradient descent. (Although my tights are still sensitive three days after the climb!) Surprisingly I was not feeling particularly cold (and with the right face protection my nose was not close to frozen, which happened on Monte Rosa in 2016). Even after seeing my best North Face mitt been blown away within a second of loosing grip of it! (Anyone with a spare left hand down mitt?! Because it had to be the left hand, of course!)

Obviously, this was quite disappointing as I had planned the climb for weeks, brought all the layers to face a potential -20⁰ windchill, was in good enough shape, did not feel any altitude effect, and we did not even reach the glacier. It was most frustrating as the summiting attempt would have worked so nicely in either one of the previous two days, but these are the rules of the mountaineering game, especially in an oceanic climate as in Southern Chile. And with narrow windows as those allowed by attending a one week conference. At least we were back to the BNP conference in time for the morning coffee break! I wish the conference participants hoping to summit later had better luck.

MCMC, variational inference, invertible flows… bridging the gap?

Two weeks ago, my friend [see here when climbing Pic du Midi d’Ossau in 2005!] and coauthor Éric Moulines gave a very interesting on-line talk entitled MCMC, Variational Inference, Invertible Flows… Bridging the gap?, which was merging MCMC, variational autoencoders, and variational inference. I paid close attention as I plan to teach an advanced course on acronyms next semester in Warwick. (By acronyms, I mean ABC+GAN+VAE!)

The notion in this work is that variational autoencoders are based on over-simple mean-field variational distributions, that usually produce a poor approximation of the target distribution. Éric and his coauthors propose to introduce a Metropolis step in the VAE. This leads to a more general notion of Markov transitions and a global balance condition. Hamiltonian Monte Carlo can be used as well and it improves the latent distribution approximation, namely the encoder, which is surprising to me. The steps of the Markov kernel produce a manageable transform of the initial mean field approximation, a random version of the original VAE. Manageable provided not too many MCMC steps are implemented. (Now, the flow of slides was much too fast for me to get a proper understanding of the implementation of the method, of the degree of its calibration, and of the computing cost. I need to read the associated papers.)

Once the talk was over, I went back to changing tires and tubes, as two bikes of mine had flat tires, the latest being a spectacular explosion (!) that seemingly went through the tire (although I believe the opposite happened, namely the tire got slashed and induced the tube to blow out very quickly). Blame the numerous bits of broken glass over bike paths.

200 years making history

Rundlestone Session

神々の山嶺 [the summit of the gods]

The summit of the gods is a five volume manga created by Jiro Taniguchi, who just passed away. While I do not find the mountaineering part of the story realistic [as in the above stripe], with feats and strength that seem beyond even the top himalayists like Reinhold Messner, Pierre Beghin, Abele Blanc, or Ueli Steck (to name a few), I keep re-reading the series for the unique style of the drawing, the story (despite the above), and the atmosphere of solo climbing in the 1970’s or 1980’s, especially as a testimony to Japanese climbers, as well as the perfect rendition of the call of the mountains… Reading Taniguchi’s obituaries over the weekend, I realised he was much more popular in France, where he won a prize for his drawing at the BD Festival in Angoulême in 2005, than in Japan.