## it was the spring of hope, it was the winter of despair

Posted in Kids, Travel with tags , , , , , , , , , , , on January 16, 2021 by xi'an

## shortened iterations [code golf]

Posted in Kids, pictures, Statistics, Travel with tags , , , , , , , , on October 29, 2019 by xi'an

A codegolf lazy morning exercise towards finding the sequence of integers that starts with an arbitrary value n and gets updated by blocks of four as

$a_{4k+1} = a_{4k} \cdot(4k+1)\\ a_{4k+2} = a_{4k+1} + (4k+2)\\ a_{4k+3} = a_{4k+2} - (4k+3)\\ a_{4k+4} = a_{4k+3} / (4k+4)$

until the last term is not an integer. While the update can be easily implemented with the appropriate stopping rule, a simple congruence analysis shows that, depending on n, the sequence is 4, 8 or 12 values long when

$n\not\equiv 1(4)\\ n\equiv 1(4)\ \text{and}\ 3(n-1)+4\not\equiv 0(32)\\ 3(n-1)+4\equiv 0(32)$

respectively. But sadly the more interesting fixed length solution

~=rep #redefine function
b=(scan()-1)*c(32~4,8,40~4,1,9~3)/32+c(1,1,3,0~3,6,-c(8,1,9,-71,17)/8)
b[!b%%1] #keep integers only


ends up being longer than the more basic one:

a=scan()
while(!a[T]%%1)a=c(a,d<-a[T]*T,d+T+1,e<-d-1,e/((T<-T+4)-1))
a[-T]


where Robin’s suggestion of using T rather than length is very cool as T has double meaning, first TRUE (and 1) then the length of a…

## Nature tidbits

Posted in Books, Statistics, University life with tags , , , , , , , , , , , on September 18, 2018 by xi'an

“Louis Chen was technically meant to retire in 2005. The mathematician at the National University of Singapore was turning 65, the university’s official retirement age. But he was only five years into his tenure as director of the university’s new Institute for Mathematical Sciences, and the university wanted him to stay on. So he remained for seven more years, stepping down in 2012. Over the next 18 months, he travelled and had knee surgery, before returning in summer 2014 to teach graduate courses for a year.”

And [yet] another piece on the biases of AIs. Reproducing earlier papers discussed here, with one obvious reason being that the learning corpus is not representative of the whole population, maybe survey sampling should become compulsory in machine learning training degrees. And yet another piece on why protectionism is (also) bad for the environment.

## un lagarto en las Cataratas del Iguazú [guest jatp]

Posted in Kids, pictures, Travel with tags , , , , , on January 10, 2017 by xi'an

## Statistics may be harmful to your freedom

Posted in Statistics with tags , , , , , on January 29, 2013 by xi'an

On Wednesday, I was reading the freshly delivered Significance and esp. the several papers therein about statisticians being indicted, fired, or otherwise sued for doing statistics. I mentioned a while ago the possible interpretations of L’Aquila verdict (where I do not know whether any of the six scientists is a statistician), but did not know about Graciela Bevacqua‘s hardship in the Argentinian National Statistics Institute, nor about David Nutt being sacked from the Advisory Council on the Misuse of Drugs, nor about Peter Wilmshurst being sued by NMT (a US medical device corporation) for expressing concern about a clinical trial they conducted. What is most frightening in those stories is that those persons ended up facing those hardships without any support from their respective institutions (quite the opposite in two cases!). And then, on the way home, I further read that the former head of the Greek National Statistics Institute (Elstat) was fired and indicted for over-estimating the Greek deficit, after resisting official pressure to lower it down…  Tough job!