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!
Archive for the Kids Category
more, please!
Posted in Books, Kids, R, Statistics with tags Charles Dickens, mathematical puzzle, Oliver Twist, R, The Riddler on February 26, 2021 by xi'anfolded Normals
Posted in Books, Kids, pictures, R, Running, Statistics with tags Annals of Applied Statistics, EM algorithm, folded normal, La Butte aux Cailles, letter to the editor, maximum likelihood estimation, nlm, outdoor swimming, Paris, R, Rfast, swimming pool, wikipedia on February 25, 2021 by xi'anWhile 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”]
Posted in Kids, pictures, Travel with tags air pollution, carbon capture, carbon tax, climate change, CO2, France Inter, polluters, sea, UN Environment, United Nations, whales on February 21, 2021 by xi'anShades of magic [book review]
Posted in Books, Kids with tags book reviews, Harry Potter, London, Neil Gaiman, Oxford, Philip Pullman, young adult books on February 20, 2021 by xi'anAfter 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