Archive for talk

the future of conferences

Posted in Books, Kids, pictures, Travel, University life with tags , , , , , , , , , , , , , on January 22, 2019 by xi'an

The last issue of Nature for 2018 offers a stunning collection of science photographs, ten portraits of people who mattered (for the editorial board of Nature), and a collection of journalists’ entries on scientific conferences. The later point leading to interesting questioning on the future of conferences, some of which relate to earlier entries on this blog. Like attempts to make them having a lesser carbon footprint, by only attending focused conferences and workshops, warning about predatory ones, creating local hives on different continents that can partake of all talks but reduce travel and size and still allow for exchanges person to person, multiply the meetings and opportunities around a major conference to induce “only” one major trip (as in the past summer of British conferences, or the incoming geographical combination of BNP and O’Bayes 2019), cut the traditional dreary succession of short talks in parallel in favour of “unconferences” where participants set communally the themes and  structure of the meeting (but ware the dangers of bias brought by language, culture, seniority!). Of course, this move towards new formats will meet opposition from several corners, including administrators who too often see conferences as a pretense for paid vacations and refuse supporting costs without a “concrete” proof of work in the form of a presentation.Another aspect of conference was discussed there, namely the art of delivering great talks. Which is indeed more an art than a science, since the impact will not only depend on the speaker and the slides, but also on the audience and the circumstances. As years pile on, I am getting less stressed and probably too relaxed about giving talks, but still rarely feel I have reached toward enough of the audience. And still falling too easily for the infodump mistake… Which reminds me of a recent column in Significance (although I cannot link to it!), complaining about “finding it hard or impossible to follow many presentations, particularly those that involved a large number of equations.” Which sounds strange to me as on the opposite I quickly loose track in talks with no equations. And as mathematical statistics or probability issues seems to imply the use of maths symbols and equations. (This reminded me of a short course I gave once in a undisclosed location, where a portion of the audience left after the first morning, due to my use of “too many Greek letters”.) Actually, I am always annoyed at apologies for using proper maths notations, since they are the tools of our trade.Another entry of importance in this issue of Nature is an interview with Katherine Heller and Hal Daumé, as first chairs for diversity and inclusion at N[eur]IPS. Where they discuss the actions taken since the previous NIPS 2017 meeting to address the lack of inclusiveness and the harassment cases exposed there, first by Kristian Lum, Lead Statistician at the Human Rights Data Analysis Group (HRDAG), whose blog denunciation set the wheels turning towards a safer and better environment (in stats as well as machine-learning). This included the [last minute] move towards renaming the conference as NeuroIPS to avoid sexual puns on the former acronym (which as a non-native speaker I missed until it was pointed out to me!). Judging from the feedback it seems that the wheels have indeed turned a significant amount and hopefully will continue its progress.

þe Norse farce beamer style

Posted in Statistics with tags , , , , , , , , , on November 30, 2018 by xi'an

Bayesian regression trees [seminar]

Posted in pictures, Statistics, University life with tags , , , , , , , , , , on January 26, 2018 by xi'an
During her visit to Paris, Veronika Rockovà (Chicago Booth) will give a talk in ENSAE-CREST on the Saclay Plateau at 2pm. Here is the abstract
Posterior Concentration for Bayesian Regression Trees and Ensembles
(joint with Stephanie van der Pas)Since their inception in the 1980’s, regression trees have been one of the more widely used non-parametric prediction methods. Tree-structured methods yield a histogram reconstruction of the regression surface, where the bins correspond to terminal nodes of recursive partitioning. Trees are powerful, yet  susceptible to over-fitting.  Strategies against overfitting have traditionally relied on  pruning  greedily grown trees. The Bayesian framework offers an alternative remedy against overfitting through priors. Roughly speaking, a good prior  charges smaller trees where overfitting does not occur. While the consistency of random histograms, trees and their ensembles  has been studied quite extensively, the theoretical understanding of the Bayesian counterparts has  been  missing. In this paper, we take a step towards understanding why/when do Bayesian trees and their ensembles not overfit. To address this question, we study the speed at which the posterior concentrates around the true smooth regression function. We propose a spike-and-tree variant of the popular Bayesian CART prior and establish new theoretical results showing that  regression trees (and their ensembles) (a) are capable of recovering smooth regression surfaces, achieving optimal rates up to a log factor, (b) can adapt to the unknown level of smoothness and (c) can perform effective dimension reduction when p>n. These results  provide a piece of missing theoretical evidence explaining why Bayesian trees (and additive variants thereof) have worked so well in practice.

talk in Linz [first slide]

Posted in Mountains, pictures, Running, University life with tags , , , , , , , , , on September 17, 2014 by xi'an

slideshare m’a tuer…

Posted in Books, Kids, Statistics, University life with tags , , , , , on November 16, 2011 by xi'an

This afternoon, I completely botched my talk at the workshop “Méthodes de Monte Carlo pour les problèmes inverses bayésiens en traitement des signaux et des images” thanks to a weird mishap on slideshare. As Og’s readers are aware,  I am a big fan of slideshare as a public depository for my slides. However, when I uploaded my talk this morning, “something” happens with the pdf file in that, while I was seeing a regular talk on my own computer (using acroread Paris.pdf), the output of the file on slideshare was missing integrals, sum and products! This was most embarrassing for me and most  inconvenient for the audience as I had to explain over and over the meaning of the missing symbols… I could have stopped the talk and gathered the pdf file from my laptop, of course, but this was the last session of a busy day, I was not sure the original was all-right ,and I had no USB key nor power plug with me… The audience was much sympathetic than I would have been myself. Apologies to all! The most bizarre thing is that I have been trying to reproduce the phenomenon since then, but to no avail. Every version I have downloaded from this afternoon onwards contains the right symbols (on my screen). Maybe it was due to the resolution of the local computer I was using for my presentation as it could not produce a full screen output… Anyway, an embarrassment I could have done without! (The title of this post is inspired from a famous crime story in southern France where the victim supposedly wrote “Omar m’a tuer” on a wall with her blood, committing a very unlikely grammatical mistake… This erroneous sentence became almost immediately part of the urban culture. I once got a “Robert m’a tuer…” as a course evaluation the only year I gave a course on classical testing!!! A movie on the crime came out recently.)