# A Strange Inequality.

We show how to prove a number theoretic inequality, originating from geometry, using an elementary approach.

# Multiplicity of the Determinant.

This post shows a way to quickly show that the determinant is multiplicative without getting your hands dirty.

# Rigorous Arithmetic in the Arakelov Divisor Class Group of a Number Field.

This post presents a poster of mine presented at the poster session of the 9th Algorithmic Number Theory Symphoisum.

# Inequalities.

This post shows a diagram, listing a lot of inequalities and showing implications between them.

# How to Compute the 5-adic Expansion of 1/2; or: Hensel's Lemma and (Non-Analytic) Newton Iteration.

In this post, we consider the quest of computing the 5-adic expansion of 1/2. We begin with introducing p-adic integers and numbers, and discussing when certain polynomials with coefficients in the integers have zeroes in the p-adic integers. This question is closely related to Hensel's lemma, which can be proven using an algebraic version of Newton's iteration. We use this to compute approximations of rational numbers in the p-adics, and consider which p-adic numers have an eventually periodic expansion.

# Finding Lattice Points, Finite Abelian Groups, and Explaining Algorithms.

We compare the tasks of finding points of a lattice, computing the structure of finite abelian groups and explaining algorithms. We show up relations between these three topics and, as an example, depict the baby-step giant-step algorithm for order computation, as well as Terr's modification of this algorithm.

# Homomorphisms, Tensor Products and Certain Canonical Maps.

A standard topic in linear algebra is the dual space of a vector space, as well as the canonical embedding of a vector space in its double dual. Moreover, transposition of homomorphisms in terms of dual spaces is rather well known. Something less known is that one has a canonical map from the dual of V tensored with W to the space of homomorphisms from V to W. In this abstract nonsense post, we describe these canonical maps, their interplay, and try to determine their images.

# Diagonalizable Matrices.

We consider the property of an n times n matrix of being diagonalizable. Is this property open in the standard topology, or the Zariski topology? The emphasis lies on the real and complex numbers, as well as on arbitrary algebraically closed fields.