Tigray emergency

NeurIPS without visa

I came by chance upon this 2018 entry in Synced that NeurIPS now takes place in Canada between Montréal and Vancouver primarily because visas to Canada are easier to get than visas to the USA, even though some researchers still get difficulties in securing theirs. Especially researchers from some African countries, which is exposed  in the article as one of the reasons the next ICLR takes place in Addis Ababa. Which I wish I could attend! In the meanwhile, I will be taking part in an ABC workshop in Vancouver, December 08, prior to NeurIPS 2019, before visiting the Department of Statistics at UBC the day after. (My previous visit there was in 1990, I believe!) Incidentally but interestingly, the lottery entries for NeurIPS 2019 are open till September 25, to the public (those not contributing to the conference or any of its affiliated groups). This is certainly better than having bots buying all entries within 12 minutes of the opening time!

More globally, this entry makes me wonder how learned societies could invest in ensuring locations for their (international) meetings allow for a maximum inclusion in terms of these visa difficulties, but also ensuring freedom and safety for all members. Which may prove a de facto impossibility. For instance, Ethiopia has a rather poor record in terms of human rights and, in particular, homosexuality is criminalised there. An alternative would be to hold the conferences in parallel locations chosen to multiply the chances for this inclusion, but this could prove counter-productive [for inclusion] by creating groups that would never ever meet. An insolvable conundrum?

an independent sampler that maximizes the acceptance rate of the MH algorithm

An ICLR 2019 paper by Neklyudov, Egorov and Vetrov on an optimal choice of the proposal in an independent Metropolis algorithm I discovered via an X validated question. Namely whether or not the expected Metropolis-Hastings acceptance ratio is always one (which it is not when the support of the proposal is restricted). The paper mentions the domination of the Accept-Reject algorithm by the associated independent Metropolis-Hastings algorithm, which has actually been stated in our Monte Carlo Statistical Methods (1999, Lemma 6.3.2) and may prove even older. The authors also note that the expected acceptance probability is equal to one minus the total variation distance between the joint defined as target x Metropolis-Hastings proposal distribution and its time-reversed version. Which seems to suffer from the same difficulty as the one mentioned in the X validated question. Namely that it only holds when the support of the Metropolis-Hastings proposal is at least the support of the target (or else when the support of the joint defined as target x Metropolis-Hastings proposal distribution is somewhat symmetric. Replacing total variation with Kullback-Leibler then leads to a manageable optimisation target if the proposal is a parameterised independent distribution. With a GAN version when the proposal is not explicitly available. I find it rather strange that one still seeks independent proposals for running Metropolis-Hastings algorithms as the result will depend on the family of proposals considered and as performances will deteriorate with dimension (the authors mention a 10% acceptance rate, which sounds quite low). [As an aside, ICLR 2020 will take part in Addis Abeba next April.]

Toukoul, Brussels

While in Brussels this week, I realised I was staying near a well-rated Ethiopian restaurant called Toukoul (from the name of a, Ethiopian hut) and went there early enough to secure a table before it got full. For plenty of good reasons as the food is terrific, with enough spice for the taste

to linger in the mouth long after the dish is gone. (Contrary to the few other Ethiopian restaurants I tested and tasted in the past months.) And plenty of injera available on the table. And a highly friendly service. A place to remember for future trips to Brussels. Definitely!