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# Category Archives: Mathematics Within the Last 100 Years

## How do I Solve this Equation? Look at the Symmetries! – The Idea behind Galois Theory

Originating author is Timo Leuders. Introduction There are some questions that accompany the development of mathematics through cultures and ages. One of these questions is how to find an unknown quantity of which one knows some relations such as – … Continue reading

## Trading in a Town

Originating authors are Alberto A. Pintoa (University of Porto, cLIAAD-INESC Porto LA) and Telmo Parreira (University of Minho, cLIAAD-INESC Porto LA). Have you ever been frustrated by the lack of choices when you go to buy something? Why do producers … Continue reading

## How Google works: Markov chains and eigenvalues

Originating author is Christiane Rousseau. From its very beginning, Google became “the” search engine. This comes from the supremacy of its ranking algorithm: the PageRank algorithm. Indeed, with the enormous quantity of pages on the World-Wide-Web, many searches end up … Continue reading

## Dimension

Originating author is Christiane Rousseau. How do we measure the size of a geometric object? For subsets of the plane we often use perimeter, length, area, diameter, etc. These are not sufficient to describe fractals. The fractal objects are very … Continue reading

## Fair voting: the quest for gold

Originating authors are Gabriel Rosenberg and Mark Iwen. It is a little known fact that two gold medals were awarded for the same pairs figure skating competition in the 2002 Winter Olympics. These two medals were ultimately a result of … Continue reading

## Goodstein Sequences: The Power of a Detour via Infinity

Originating authors are Michèle Artigue, Ferdinando Arzarello and Susanna Epp. Studying the evolution of a natural phenomenon often leads to studying numerical sequences , especially their long-term behavior and whether they eventually converge. Polynomial, exponential, and logarithmic sequences are frequently … Continue reading

## Matrices and Digital Images

Originating authors are Dirce Uesu Pesco and Humberto José Bortolossi. The images you see on internet pages and the photos you take with your mobile phone are examples of digital images. It is possible to represent this kind of image … Continue reading

## Banach’s microscope to find a fixed point

Originating author is Christiane Rousseau. In this vignette, we will show how we start from a small game to discover one of the most powerful theorems of mathematics, namely the Banach fixed point theorem. This theorem has fantastic applications inside … Continue reading

## What is the way of packing oranges? — Kepler’s conjecture on the packing of spheres

Originating author is Christiane Rousseau. What is the densest packing of spheres? Kepler conjectured that it was the one you observe with oranges at the fruit shop, and which is called the face-centered cubic lattice (Figure 1). At the International … Continue reading

## Higher Dimensions

Originating authors are Markus Ruppert and Hans-Georg Weigand. 1. Looking for the next dimension Does our world really have more than three dimensions? If so, do objects in higher dimension have a relation to the world around us? Is it … Continue reading