dependable AI/ML [France is AI]

the future of conferences

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

Bayesian regression trees [seminar]

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]