## Archive for Vienna

## 1:59:40!

Posted in pictures, Running, Travel with tags Austria, Eliud Kipchoge, Kenya, marathon, pacemakers, sub-two-hours marathon, unofficial record, Vienna, Wien, Wiener Prater on October 12, 2019 by xi'an## from here to infinity

Posted in Books, Statistics, Travel with tags Bayesian inference, classification, Clermont-Ferrand, clustering, Dirichlet process mixture, From Here to Infinity, hyperparameter, Ian Stewart, label switching, mixtures of distributions, prior distributions, sparse finite mixtures, University of Warwick, Vienna on September 30, 2019 by xi'an

“Introducing a sparsity prior avoids overfitting the number of clusters not only for finite mixtures, but also (somewhat unexpectedly) for Dirichlet process mixtures which are known to overfit the number of clusters.”

**O**n my way back from Clermont-Ferrand, in an old train that reminded me of my previous ride on that line that took place in… 1975!, I read a fairly interesting paper published in Advances in Data Analysis and Classification by [my Viennese friends] Sylvia Früwirth-Schnatter and Gertrud Malsiner-Walli, where they describe how sparse finite mixtures and Dirichlet process mixtures can achieve similar results when clustering a given dataset. Provided the hyperparameters in both approaches are calibrated accordingly. In both cases these hyperparameters (scale of the Dirichlet process mixture versus scale of the Dirichlet prior on the weights) are endowed with Gamma priors, both depending on the number of components in the finite mixture. Another interesting feature of the paper is to witness how close the related MCMC algorithms are when exploiting the stick-breaking representation of the Dirichlet process mixture. With a resolution of the label switching difficulties via a point process representation and k-mean clustering in the parameter space. *[The title of the paper is inspired from Ian Stewart’s book.]*

## logicomix redux

Posted in Books, Kids, pictures, University life with tags 50 years, Bertrand Russell, book reviews, Christos Papadimitrou, comics, commemoration, France, logicomix, Ludwig Wittgenstein, Paris, Principia, self-referential books, Université Paris Dauphine, Vienna on May 31, 2019 by xi'an*I* had not made the link until the last speaker of the 50 years of Dauphine commemoration was introduced that he was one of the authors of Logicomix. He spoke of the mathematical modeling of neurons and brain activity, rather than comics, but at a very low level that he called cartoonesque. It is a rare event that cartoon characters can be met in the flesh!

## Der Kunst ihre Freiheit [and the scare of the nude]

Posted in Books, pictures, Travel with tags #DerKunstihreFreiheit, #ToArtItsFreedom in English, advertising, censorship, Egon Schiele, Facebook, London, London Tube, modernism, nude, poster, Vienna, Wien, Wiener Moderne 2018 on February 17, 2018 by xi'an**A** poster campaign advertising for several exhibits of modernist painters in Vienna, including major paintings by Egon Schiele, has met with astonishing censoring from the transport companies posting these advertisements. (And by Facebook, which AIs are visibly too artificial and none too intelligent to [fail to] recognise well-known works of art.) Not very surprising, given the well-known conservatism of advertising units in transportation companies, but nonetheless appalling, especially when putting these posters against the truly indecent ones advertising for, e.g., gas guzzling machines and junk food.

## Nature snapshots [and snide shots]

Posted in Books, pictures, Statistics, Travel, University life with tags Bayesian inference, Boltzmann machines, corrigendum, machine learning, Nature, neural network, principal components, quantum computers, quantum comuting, statues, typewriter, Vienna on October 12, 2017 by xi'an**A** very rich issue of Nature I received [late] just before leaving for Warwick with a series of reviews on quantum computing, presenting machine learning as the most like immediate application of this new type of computing. Also including irate letters and an embarassed correction of an editorial published the week before reflecting on the need (or lack thereof) to remove or augment statues of scientists whose methods were unethical, even when eventually producing long lasting advances. (Like the 19th Century gynecologist J. Marion Sims experimenting on female slaves.) And a review of a book on the fascinating topic of Chinese typewriters. And this picture above of a flooded playground that looks like a piece of abstract art thanks to the muddy background.

“Quantum mechanics is well known to produce atypical patterns in data. Classical machine learning methods such as deep neural networks frequently have the feature that they can both recognize statistical patterns in data and produce data that possess the same statistical patterns: they recognize the patterns that they produce. This observation suggests the following hope. If small quantum information processors can produce statistical patterns that are computationally difficult for a classical computer to produce, then perhaps they can also recognize patterns that are equally difficult to recognize classically.”Jacob Biamonte et al., Nature, 14 Sept 2017

One of the review papers on quantum computing is about quantum machine learning. Although like Jon Snow I know nothing about this, I find it rather dull as it spends most of its space on explaining existing methods like PCA and support vector machines. Rather than exploring potential paradigm shifts offered by the exotic nature of quantum computing. Like moving to Bayesian logic that mimics a whole posterior rather than produces estimates or model probabilities. And away from linear representations. (The paper mentions a O(√N) speedup for Bayesian inference in a table, but does not tell more, which may thus be only about MAP estimators for all I know.) I also disagree with the brave new World tone of the above quote or misunderstand its meaning. Since atypical and statistical cannot but clash, “universal deep quantum learners may recognize and classify patterns that classical computers cannot” does not have a proper meaning. The paper contains a vignette about quantum Boltzman machines that finds a minimum entropy approximation to a four state distribution, with comments that seem to indicate an ability to simulate from this system.