## Notes on “Haskell Programming – from first principles”

From November, 13th 2017 to June, 9th 2018, a friend and I were working our way through the 1285 pages of “Haskell Programming – from first principles” by Christopher Allen and Julie Moronuki. That’s more than six pages per day! While reading and discussing, I took a few notes here and there, which I want to publish in this post. Some of the sentences are directly taken from the book, which I highly recommend to anyone who wants to learn Haskell, by the way. Continue reading Notes on “Haskell Programming – from first principles”

## LaTeX Plot Snippets

The LaTeX package tikz contains a set of commands that can render vector based graphs and plots. This post contains several examples which are intended to be used as a cut-and-paste boilerplate. Each sample comes with a screenshot and a snippet that contains the relevant parts of the LaTeX source code. The entire source code can be examined by clicking onto the individual images. Continue reading LaTeX Plot Snippets

## Graph Theory Overview

In the field of computer science, a graph is an abstract data type that is widely used to represent connections and relationships. This post gives an overview about a selection of definitions, terms, and algorithms, which are related to graphs. The content was put together during preparation for a theoretical computer science test at Cooperative State University Baden-Württemberg and is mostly taken from either Wikipedia or lecture notes. Continue reading Graph Theory Overview

## Least Squares Derivation

The least squares optimization problem searches for a vector, that minimizes the euclidean norm in the following statement as much as possible: $$x_\text{opt}=\arg\min_x\frac{1}{2}\left\lVert Ax-y\right\rVert^2_2\,.$$This article explains how $x_\text{opt}=(A^\top A)^{-1}A^\top y$, the solution to the problem, can be derived and how it can be used for regression problems. Continue reading Least Squares Derivation

## Cubic Spline Interpolation

Cubic spline interpolation is a mathematical method commonly used to construct new points within the boundaries of a set of known points. These new points are function values of an interpolation function (referred to as spline), which itself consists of multiple cubic piecewise polynomials. This article explains how the computation works mathematically.

After an introduction, it defines the properties of a cubic spline, then it lists different boundary conditions (including visualizations), and provides a sample calculation. Furthermore, it acts as a reference for the mathematical background of the cubic spline interpolation tool on tools.timodenk.com which is introduced at the end of the article. Continue reading Cubic Spline Interpolation

## Guess Solutions of Polynomials

For a given polynomial of $n$th degree

$$P_n(x)=\sum_{i=0}^n a_ix^i = a_nx^n+a_{n-1}x^{n-1}+…+a_1x+a_0$$

you can guess rational solutions $x$ for the corresponding problem $P_n(x)=0$ by applying the following two rules:

1. $$x=\frac{p}{q}\text{, with } p \in \mathbb{Z} \land q \in \mathbb{N}\land p\mid a_0 \land q\mid a_n$$
2. $$\lvert x\rvert\le2\cdot \max\left\lbrace \sqrt[k]{\frac{\lvert a_{n-k}\rvert}{\lvert a_n\rvert}}, k=1, …, n\right\rbrace$$

## Trigonometric Functions Formulary

This formulary has been created during the online onboarding process at Baden-Wuerttemberg Cooperative State University (DHBW). It is suitable for the related online tests and might be helpful for other people, seeking for formulas in this field of mathematics.

##### Basics

$$\begin{array}{l} \tan x = \frac{{\sin x}}{{\cos x}}\\ \cot x = {\tan ^{ – 1}}x = \frac{{\cos x}}{{\sin x}} \end{array}$$ Continue reading Trigonometric Functions Formulary