Archive for the Running Category

O’Bayes 19: registration and travel support

Posted in pictures, Running, Travel, University life with tags , , , , , , , on February 14, 2019 by xi'an

An update about the O’Bayes 19 conference next June-July:  the early registration period has now opened. And there should be funds for supporting early-career researchers, thanks to Google and CNRS sponsorships, as detailed below:

Early-career researchers less than four years from PhD, are invited to apply for early-career scholarships. If you are a graduate student, postdoctoral researcher or early-career academic and you are giving a poster, you are eligible to apply. Female researchers and underrepresented minorities are especially encouraged to apply. Selected applicants will receive up to £450, which can be used for any combination of fees, travel and accommodation costs, subject to receipts.

The deadline for applying is the 15th of March (which is also the deadline to submit the abstract for the poster) and it has to be done at the registration phase via the dedicated page. Those who have submitted an abstract before this information on scholarships was made available (11 Feb.) and applying for travel support should contact the organisers.

missing digit in a 114 digit number [a Riddler’s riddle]

Posted in R, Running, Statistics with tags , , , , , , , on January 31, 2019 by xi'an

A puzzling riddle from The Riddler (as Le Monde had a painful geometry riddle this week): this number with 114 digits

530,131,801,762,787,739,802,889,792,754,109,70?,139,358,547,710,066,257,652,050,346,294,484,433,323,974,747,960,297,803,292,989,236,183,040,000,000,000

is missing one digit and is a product of some of the integers between 2 and 99. By comparison, 76! and 77! have 112 and 114 digits, respectively. While 99! has 156 digits. Using WolframAlpha on-line prime factor decomposition code, I found that only 6 is a possible solution, as any other integer between 0 and 9 included a large prime number in its prime decomposition:

However, I thought anew about it when swimming the next early morning [my current substitute to morning runs] and reasoned that it was not necessary to call a formal calculator as it is reasonably easy to check that this humongous number has to be divisible by 9=3×3 (for else there are not enough terms left to reach 114 digits, checked by lfactorial()… More precisely, 3³³x33! has 53 digits and 99!/3³³x33! 104 digits, less than 114), which means the sum of all digits is divisible by 9, which leads to 6 as the unique solution.

 

free fall [fake]

Posted in Mountains, pictures, Running, Travel with tags , , , , , , , , , , on January 12, 2019 by xi'an

As I was looking for the location of a picture serving as a background image for Windows 10 log-in page, I came across several versions of the above, supposedly showing a climber failing to grab another climber’s hand and as a result falling. Or “falling” as the image is obviously doctored, most likely by removing the ropes securing both climbers. This is fairly ridiculous, from the top climber hanging by his hand to the bottom one carrying quickdraws on his harness, as in the worst climbing movies… Still, I wish the location of the shot was provided on the website. (As an insider joke, I had a fall when running that was definitely not fake during the Xmas vacations, scraping a fair amount of skin on the gritty sidewalk, but with no apparent lasting damage, although I am barred from running by a tendinitis which started in Warwick last month..!)

a question from McGill about The Bayesian Choice

Posted in Books, pictures, Running, Statistics, Travel, University life with tags , , , , , , , on December 26, 2018 by xi'an

I received an email from a group of McGill students working on Bayesian statistics and using The Bayesian Choice (although the exercise pictured below is not in the book, the closest being exercise 1.53 inspired from Raiffa and Shlaiffer, 1961, and exercise 5.10 as mentioned in the email):

There was a question that some of us cannot seem to decide what is the correct answer. Here are the issues,

Some people believe that the answer to both is ½, while others believe it is 1. The reasoning for ½ is that since Beta is a continuous distribution, we never could have θ exactly equal to ½. Thus regardless of α, the probability that θ=½ in that case is 0. Hence it is ½. I found a related stack exchange question that seems to indicate this as well.

The other side is that by Markov property and mean of Beta(a,a), as α goes to infinity , we will approach ½ with probability 1. And hence the limit as α goes to infinity for both (a) and (b) is 1. I think this also could make sense in another context, as if you use the Bayes factor representation. This is similar I believe to the questions in the Bayesian Choice, 5.10, and 5.11.

As it happens, the answer is ½ in the first case (a) because π(H⁰) is ½ regardless of α and 1 in the second case (b) because the evidence against H⁰ goes to zero as α goes to zero (watch out!), along with the mass of the prior on any compact of (0,1) since Γ(2α)/Γ(α)². (The limit does not correspond to a proper prior and hence is somewhat meaningless.) However, when α goes to infinity, the evidence against H⁰ goes to infinity and the posterior probability of ½ goes to zero, despite the prior under the alternative being more and more concentrated around ½!

waiting for the red lights to change

Posted in pictures, Running, Travel with tags , , , , , on December 22, 2018 by xi'an

mare e monti [climbing up Rumpe Cuou]

Posted in Mountains, pictures, Running, Travel with tags , , , , , , , , , , , on December 18, 2018 by xi'an

While at CIRM for Bayes for Good and Big Bayes workshops, I went again climbing with Nicolas, a guide from Cassis. As we had picked a day when the mistral (a local Northeasterner) was high and made climbing unpleasant and freezing, Nicolas picked a domain on the `other’ side, that was completely protected and started from the sea and went up in the sun, the wind only hitting us at the top, after six pitches, most of which I managed to lead.

We proceeded fast enough to get down for a second route, just as pleasant, finishing at the top as the Sun was setting down behind the islands below us. A well-chosen set of levels (5b, 5c) and rock-types like slab for my level and a nice conslusion to three climbing outings within a month. (Note that most pictures of our route are not mine as my camera battery went down before we even started.)

Venus at dawn

Posted in pictures, Running, Travel with tags , , , , , , , on December 14, 2018 by xi'an