## Archive for the Kids Category

## a rush to grade

Posted in Kids, pictures, Statistics, University life with tags biking, correction, COVID-19, cycle path, France, grading, inverse Gaussian distribution, lockdown, midterms, pandemic, Paris on October 29, 2020 by xi'an## artificial EM

Posted in Books, Kids, R, Statistics, University life with tags cross validated, EM algorithm, fixed point, joint distribution, maximum likelihood estimation, something is wrong on the Internet, wikipedia on October 28, 2020 by xi'an**W**hen addressing an X validated question on the use of the EM algorithm when estimating a Normal mean, my first comment was that it was inappropriate since there is no missing data structure to anchor by (right preposition?). However I then reflected upon the infinite number of ways to demarginalise the normal density into a joint density

∫ f(x,z;μ)dz = φ(x–μ)

from the (slice sampler) call to an indicator function for f(x,z;μ) to a joint Normal distribution with an arbitrary correlation. While the joint Normal representation produces a sequence converging to the MLE, the slice representation utterly fails as the indicator functions make any starting value of μ a fixed point for EM.

Incidentally, when quoting from Wikipedia on the purpose of the EM algorithm, the following passage

Finding a maximum likelihood solution typically requires taking the derivatives of the likelihood function with respect to all the unknown values, the parameters and the latent variables, and simultaneously solving the resulting equations.

struck me as confusing and possibly wrong since it seems to suggest to seek a maximum in *both* the parameter and the latent variables. Which does not produce the same value as the observed likelihood maximisation.

## help for Cox’s Bazar

Posted in Kids, pictures, Travel with tags Bangladesh, Cox's Bazar, donation, hunger, refugees, Rohingyas, UN, United Nations Population Fund on October 25, 2020 by xi'an## Nous continuerons, Professeur.

Posted in Kids, pictures with tags Emmanuel Macron, France, French history, high school, La Sorbonne, Panthéon, Paris, religions, teaching on October 24, 2020 by xi'an

“Nous continuerons, Professeur. Avec tous les instituteurs et professeurs de France, nous enseignerons l’histoire, ses gloires comme ses vicissitudes. Nous ferons découvrir la littérature, la musique, toutes les œuvres de l’âme et de l’esprit. Nous aimerons de toutes nos forces le débat, les arguments raisonnables, les persuasions aimables. Nous aimerons la science et ses controverses. Comme vous, nous cultiverons la tolérance. Comme vous, nous chercherons à comprendre, sans relâche, et à comprendre encore davantage cela qu’on voudrait éloigner de nous. Nous apprendrons l’humour, la distance. Nous rappellerons que nos libertés ne tiennent que par la fin de la haine et de la violence, par le respect de l’autre.”Emmanuel Macron, 21 October 2020