Ruben’s blog

The finite element method

The finite element method is an elegant mathematical method to numerically solve partial differential equations. In this article, I give a short introduction.

The singular value decomposition

The singular value decomposition is a matrix decomposition with many applications, one of them being principal component analysis. In this article I use the spectral theorem for Hermitian matrices to easily prove the existence of the singular value decomposition.

Cardano's formula

Cardano's formula is an analogue of the quadratic formula for polynomials of degree three. One can find many proofs of the formula online, but most of them are not very instructive. In this article I present that the formula can be derived by completing the cube (as an analogy to completing the square).

The spectral theorem for Hermitian matrices

This article proves some pleasing properties of Hermitian matrices, and uses them to prove that Hermitian matrices can be diagonalized in a specific form.

A simpler form of the quadratic formula

Most of us had to learn the quadratic formula in high school. In this article I argue that a technique called `completing the square´ is more useful and should be used instead.

Euler's formula for connected planar graphs

Euler's formula for connected planar graphs shows a pleasing relation between the number of vertices, edges, and faces in a planar graph. In this article I show how to derive the formula.

The Euler-Lagrange equation

The Euler-Lagrange equation is an import equation which is useful when you try to find a extrema of functionals, which are mappings from functions to the real numbers. In this article I show a derivation and some applications.