Marcel Popescu

Probabilities are hard. As an example, there's a known puzzle: a family has two children; if one of them is a girl, what is the probability that the other one is also a girl? The answer, un-intuitively, is not 1/2 but 1/3. There are various explanations but – as with the Monty Python puzzle years ago – I wanted to write code to check it out, so I wrote the following using LinqPad: void Main() { var rnd = new Random(); // Generate a random set of families with two children; true means girl, false means boy var all = Enumerable.Range(1, 10000).Select(_ => new Pair(rnd.Next(2) == 0, rnd.Next(2) == 0)).ToList(); // Extract only the families with at least one girl var oneGirl = all.Where(it => it.First || it.Second).ToList(); // Out of those families, how many have two girls? The result should be 1/3rd var otherGirl = oneGirl.Where(it => it.First && it.Second).ToList(); Console.Wri...

I just discovered a surprisingly simple (and obvious in hindsight) algorithm for calculating the week index of a given date. For example, April 15th is in the 3rd week (or the 3rd Tuesday of the month). I was going to do the usual thing and just Google for it but then I realized that the solution is extremely simple: private static int GetWeekPosition(DateTime date) { // the position of the given date is how many times I can subtract 7 days (go back one week) and still be in the same month // in other words, it's the integer part of (day / 7) return date.Day / 7; } (I am returning a base-zero result, but you can of course add 1 if you need it.) I realize this is not the answer to the Universe or anything but I thought it's interesting.

I've long used the expression "real science, so called because it can only be found in books and movies". From a talk at Pycon 2014 : The ideals reality of science: The pursuit of verifiable answers highly cited papers for your c.v. The validation of our results by reproduction convincing referees who did not see your code or data An altruistic, collective enterprise A race to outrun your colleagues in front of the giant bear of grant funding H.T to Daniel Lemire .