Introduction The cross validation is a common technique to calibrate the binwidth histogram. They are the simplest and, sometimes, the most effective tool to describe the density of some dataset.

Smallest multiple 2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder. What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?

Largest palindrome1 product A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 x 99.

Largest prime factor The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143 ?

Even Fibonacci numbers Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, … By considering the terms in the Fibonacci sequence whose values do not exceed four …

Motivation I remember one lecture about linear models in the University of Costa Rica. He said before to present some classic method “This only works if you have more data than variables”. In this moment, it seems very reasonable and I could not imagine any real case with more variables ($p$) than data ($n$).

Let’s help them out to go to the competition The guys from the Mathematics Olympics Team are in a fundraiser. Now is to assist to the V Ibero-American Inter-universitary Math Competition (CIIM because of its initials in Spanish). The competition will be in Armenia, Colombia the 15th to the 20th October, 2013. If want …

The monthly section “Talento destacado del mes” from the TICOTAL network (Red de Talento Costarricense en el Extranjero, in Spanish) made me an interview about my experience as Ph.D student in France. I talked about the process at the University of Costa Rica (UCR) to get the international scholarship which is a strange story. Back …

The other day I was bounding some inequalities for my thesis. I had that some functions were Holder, but I haven’t the explicit derivatives of my functions. I spent one hour or so thinking if I could bound correctly my expression without having the derivatives. The answer is yes, and I will show how. Hölder …

This week I gave a talk about the advantages of using Git with $ \LaTeX$ files. This talk was presented in the Mathematics Colloquiums organized by the department of mathematics of the University of Costa Rica .