Home Page - Philipp K. Janert on Philipp K. Janert, Ph.D.

Let $G$ be a finite group with $n$ elements, and $H$ a subgroup of $G$ with $m$ elements.

What methods are there to connect an external (USB) drive or memory stick to a Linux box most conveniently?

In my previous post on one-dimensional heat flow, I encountered sums of the form: $$ \sum_{n=0}^\infty \frac{\pm 1}{2n+1} \exp \left( - (2n+1)^2 x \right) $$ A plot (involving the first 1000 terms) is shown below, and looks reasonable enough.

Imagine a rod that is initially at temperature $T_1$ and then brought into an environment with a lower temperature $T_0 < T_1$.

Like many other people, I have struggled with git.

Git has been around for going on 20 years, yet people still continue to write “getting-started” and “common-challenges” tutorials.

How short can a complete, competitive sort algorithm be?

“If you want to go fast, go alone; if you want to go far, go together.”

About a year ago, to put a cap on my struggles with Hugo, I wrote up some thoughts on the whole static-site-generator (SSG) concept.

They use a “real database”.

Building open-source software from source is not necessarily hard: after all, typing make is fairly easy.

Selecting a random element from an array of length n is easy: simply generate a random integer i, with 0 <= i < n, and use the array element at that index position.

Shuffling a collection of items is a surprisingly frequent task in programming: essentially, it comes up whenever a known input must be processed in random order.

The Nelder-Mead-Algorithm (also known as the “Simplex Algorithm” or even as the “Amoeba Algorithm”) is an algorithm for the minimization of non-linear functions in several variables.

When writing programs that do computations, my overwhelming preference is to simply write results to standard output, and to use shell redirection to capture the output in a file.

Having used Hugo for a some years now, while creating a few dozen entries, I have discovered a few “best practices” for organizing the raw (Markdown) content.

Among my favorite features of the Go language is the fact that Go has concurrency and network programming “natively” built in.

QR codes are a two-dimensional equivalent of barcodes: a graphical encoding of information, which in practice means a string of about 4000 alpha-numeric characters (upper-case only) or a little less than 3000 arbitrary bytes.

Sharing files across computers on a local, “informal” (home) network is a recurring desire.

Entirely by chance, while looking over the event calendar of Bike PGH, I came across the Rail 66 Clarion Summerfest 2023 Time Trial.

Imagine a shared resource, such as a compute server.

The (notorious) Dirac delta-function is usually introduced as a function with the following properties: \[ \delta(x) = \begin{cases} 0 & \qquad x \neq 0 \\ \text{“$\infty$”} & \qquad x = 0 \end{cases} \]

Over the holidays, I sat down and wrote a casual turn-based strategy game.

Over the holidays, I had the opportunity to work on a spare time project, and so I sat down and wrote a casual, turn-based strategy game; a variant (you might say: a clone) of the KDE game Konquest.

Finding a realistic (or at least, realistic looking) initial configuration of game objects or simulation particles can be a challenge.

I have started to get interested in Hidden Markov Models (HMM).

This site is generated using Hugo.

The “Newsvendor Problem” is a classic problem in inventory and supply-chain management: how much product to carry in stock in the face of uncertain demand?

In a moment of nostalgia, I picked up my copy of “The Art of UNIX Programming” by Eric S.

Processing command-line arguments in ad-hoc python tools is one of those areas where I tend to just hack it together from scratch — simply because the effort of learning and understanding the relevant library packages not only seems to be more work than it

I recently got interested in algorithms for scaling pixel art images, such as icons or video game sprites.

Containers are not usually associated with GUI applications, but there may be times when one might still want to run such a program inside a container, for example to isolate the application’s dependencies.

In praise of what?

In a previous post, I explored the possibilities of running a GUI application inside a Docker container.

There are problems playing the pysolfc solitaire game on the latest release of Linux Mint 21 (Vanessa).

Containers are not usually associated with GUI applications, but there may be times when one might still want to run such a program inside a container, for example to isolate the application’s dependencies.

The freedesktop project, arguably the most important Linux organization you’ve never heard of, has (among many other noble deeds) done an admirable job clearing up the mess of local cache and config files in one’s home directory.

I occasionally see references to the HDF5 file format, but I have never encountered it in the wild.

George H.

The Altitude Theorem or Geometric Mean Theorem is a result from high-school geometry.

I just wasted one hour and five minutes, dealing with two of these opaque, unexpected, and almost undiagnosable showstopper roadblocks that Hugo will throw your way - much too often, in my opinion.

The Diamond-Square Algorithm is the natural first stop for generating artificial landscapes.

I recently came across a collection of old (1990s) “programming challenges”.

When doing research to get this website up and running, I came across the following two truly inspiring examples:

The most exciting phrase to hear in science, the one that heralds new discoveries, is not “Eureka!”

I learned Unix almost 30 years ago, while attending graduate school in the early 90s, from a now long-obsolete book entitled “Unix for the Impatient”.

Hugo is a static site generator: it takes some plain-text content, marries it to a bunch of HTML templates, and produces a set of complete, static HTML pages that can be served by any generic, stand-alone web server.

I have compiled my various write-ups on the Hugo site generator into a single, consecutive guide.

Analytic number theory is the application of methods from analysis to the study of integers, in particular primes.

I came across an unexpected problem when using Mathjax in a Markdown document (to be used with the Hugo site generator).