Archive for alpine climbing

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

Posted in Books, Mountains, Running, Statistics, Travel, University life with tags , , , , , , , , , , , , , , , , , on October 2, 2020 by xi'an

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

Posted in Statistics with tags , , , , , , , , , on March 11, 2020 by xi'an

Rundlestone Session

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

神々の山嶺 [the summit of the gods]

Posted in Books, Kids, Mountains, pictures with tags , , , , , , , , , , , on February 19, 2017 by xi'an

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.