Archive for swimming pool

Tour de Paris [of pools]

Posted in Kids, pictures, Running, Travel with tags , , , , , , , on April 25, 2021 by xi'an

As I am prevented from running since the beginning of this year, due to a ligament injury caused by an excess of kilometers run since the beginning of the (first) lockdown, I have started swimming most days I can find a free window of time. And an open swimming pool! While Paris and most of the suburban cities near me have a decent offer of (cheap) public pools, it is often a challenge to find one open at a manageable time. Meaning for me mostly in the early morning. The lockdown has obviously reduced opening hours and introduced restricted access, requiring a medical certificate for indoor pools, and I have thus being recently visiting a rather extensive array of pools to fit such constraints, since both nearby pools, at home and at work, are rarely available. Last week, I biked to the most exotic so far, namely a pool made from a barge standing on the Seine River. It is alas not yet outdoor, but not yet crowded either (if small and rather hot). By comparison, the nearer and wider pool at Porte d’Orléans is surprisingly crowded at 7am (but pleasantly colder) and the historical pool on Butte aux Cailles also gets quickly crowded and is missing its outdoor pool (but is close to a fantastic bakery!). Even careful scheduling does not always work as I sometimes find an unexpected closed door, as two weeks ago when Butte aux Cailles had emptied overnight or a few days ago when Joséphine Baker had a disfunctioning pediluvium enough to bar entry. (The outdoor 50m pool in Villejuif I used to go to has just reopened to the general public and is not yet overcrowded, despite milder temperatures.)

folded Normals

Posted in Books, Kids, pictures, R, Running, Statistics with tags , , , , , , , , , , , , on February 25, 2021 by xi'an

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).

Riddle of the lanes

Posted in Books, Kids, R with tags , , , , , on July 13, 2020 by xi'an

An express riddle from the Riddler about reopening pools, where lanes are allowed provided there is no swimmer in the lane or in any of the adjacent lanes. If swimmers pick their lane at random (while they can), what is the average number of occupied lanes?

If there are n lanes and E(n) is the expected number of swimmers, E(n) satisfies a recurrence relation determined by the location of the first swimmer:

E(n)=1+\frac{1}{n}[2E(n-2)+\sum_{i=2}^{n-1}\{E(i-2)+E(n-i-1)\}]

with E(0)=0, E(1)=E(2)=1. The above can be checked with a quick R experiment:

en=0
for(t in 1:T){
   la=rep(u<-0,N)
   while(sum(la)<N){
     i=sample(rep((1:N)[!la],2),1)
     la[max(1,i-1):min(N,i+1)]=1
     u=u+1}
   en=en+u}

running in circles

Posted in Mountains, pictures, Running, Travel with tags , , , , , , , , on May 31, 2020 by xi'an

As lockdown rules concerning outdoor activities were rather restrictive (run alone, away from other people, at most one hour and at most 1km away from home), I used the network of streets around my house to design a 13km circuit that was never replicating more than intersecting previously visited roads. And I ran it every one of the 60 days of the lockdown.

This was a purely urban run on pavement only, but offered nice views of the neighbouring suburbs, with three hills to climb.

 

And hardly anyone in the streets, except for the occasional soul walking her dog. And never a single control of the laisser-passer I had to print every morn.

   

Going by the park and the local swimming pool every day and unrealistically wishing they would open soon…

trailers versus mountaineers?

Posted in Kids, Mountains, Running, Travel with tags , , , , , , , , , , , on August 31, 2019 by xi'an

A slight altercation in a swimming corridor during lunch put me back into this Le Monde paper I read yesterday about (real?!) mountaineers being annoyed at trailers, especially those currently running the Ultra-Trail du Mont Blanc (UTMB). A lady stopped me from going further for not crawling as this was a “crawl only” lane and started a lengthy tirade that I cut short by moving to another lane. I find such debates pretty absurd and rather hypocritical. When the fundamental goal is mostly to reduce the number of people on the trails, in the mountains, or in the pool by creating categories with those in and those out. This seems an unavoidable human trend that happened several times in mountaineering, from the early days when going above a certain limited was prohibited to those when climbing solo, rope-free, mixed style, without a registered guide or certificate, &tc. base-jumping, was or became taboo. It is annoying to see crowds in the mountains, whether on the Everest final sketch or on the UTMB track, for sure, but by nature these are singular events and the next peak is almost surely free. It is also annoying to find other climbers on one’s chosen route as they will certainly cause delays, but this is the nature of the game and the next route may well be free. I thus find pretty annoying that some claim their rights to enjoy mountains are higher or purer than others, whom they accuse of elitism and ill-placed competition, when themselves are far from free of the same defect.

 

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