more, please!

As The Riddler proposed for several weeks in a row a CrossProduct™ puzzle where 3 x n one-digit integers have to be deduced from their rowwise and columnwise products, I attempted writing an R solver by applying a few basic rules repeatedly, which worked for the first two puzzles, if not for the earlier one I solved by paper & pen (mostly) a few weeks ago, and again worked for the final one. The rules I used were to spot unique entries, forced entries by saturation, and forced digits (from the prime factor decomposition) again by saturation. Any further rule to add to the solver? (The R code is currently rather ugly!) Please, some more!

folded Normals

While having breakfast (after an early morn swim at the vintage La Butte aux Cailles pool, which let me in free!), I noticed a letter to the Editor in the Annals of Applied Statistics, which I was unaware existed. (The concept, not this specific letter!) The point of the letter was to indicate that finding the MLE for the mean and variance of a folded normal distribution was feasible without resorting to the EM algorithm. Since the folded normal distribution is a special case of mixture (with fixed weights), using EM is indeed quite natural, but the author, Iain MacDonald, remarked that an optimiser such as R nlm() could be called instead. The few lines of relevant R code were even included. While this is a correct if minor remark, I am a wee bit surprised at seeing it included in the journal, the more because the authors of the original paper using the EM approach were given the opportunity to respond, noticing EM is much faster than nlm in the cases they tested, and Iain MacDonald had a further rejoinder! The more because the Wikipedia page mentioned the use of optimisers much earlier (and pointed out at the R package Rfast as producing MLEs for the distribution).

what the whale?! [“whales eat carbon, not fish”]

Shades of magic [book review]

After seeing the books in a Denver bookstore (in the summer of 2019), I eventually came to try one, then the others. Even though the setting is somewhat simplistic, or may intended for young adults, with ideas also found in earlier novels, it makes for a pleasant read. The underlying concept is having several Londons set in different universes and connected by magic for the happy few able to travel between them. One of them is “our” Victorian London. Labelled as Grey London. Then there are White, Red, and Black Londons… With some pivotal pubs existing in all (?) of them. This reminded me very much of Neverwhere, one of the few Gaimans I deeply appreciated. Or of Pullman’s Oxfords. The first volume sets the scene, with two main characters, (Grey) Lila and (Red) Kell, whose paths will come to cross, some villains in the least privileged London, and some sudden existential threat on Red London. The latest being the least convincing part of the plot as lacking subtlety. The second volume mostly takes place in Red London and the first part sounds a wee bit like the female part of Red seas under red skys. That is, a smart thief at sea. And a smarter captain. With on top of it a magic competition where all main characters cross path. Again a poor part of the plot as the competition feels like Harry Potter’s Goblet of Fire, while a new danger is building up to bring the fodder for the third volume. Not completely uninteresting (I read most of it over Xmas day, by a log fire), but somewhat two-dimensional (with a surprising lack of moral reticence to kill people, most surprising for a YA series). The third volume, A conjuring of light,  is a bit more predictable, including the deaths of some major characters (one or two more would have helped). And the ending could have been less all-inclusive and rosy!,  but this was an enjoyable conclusion nonetheless.

Mars attack [live]