, 1 min read
Task at hand: Read two or more files at the same time in Perl. Solution: #!/bin/perl -W # Reading from multiple files simultaenously use strict; my ($f1,$f2); open(F1,"< $ARGV[0]") || die("Cannot open $ARGV[0]"); open(F2,"< $ARGV[1]") || die("Cannot open…
, 5 min read
pico.sh is a similar blogging platform like Bearblog. In contrast to Bearblog the upload of Markdown content is done using ssh/scp/sftp. I wrote about hosting static sites on various platforms: Hosting Static Content with surge.sh Hosting Static Content with now.sh, now.sh renamed themself to…
, 4 min read
Task at hand: You have generated static HTML files with a static site generator. You want to check, whether the links in all your files are pointing to valid URLs, and you want all your images and PDFs be present. There is a utility written in the Go programming language called htmltest. I first…
, 1 min read
Process substitution is available in ksh, bash, and zsh. More examples can be found here: Process Substitution. Process substitution uses /dev/fd/<n> files to send the results of the process(es) within parentheses to another process. Piping the output of one program to the input of another…
, 2 min read
Today, 14-Oct-2024, starting at 16:23 (CET), internet provided by Vodafone was unavailable. At 20:51 internet was available again. So for almost five hours I had no internet and the blog went dark. Luckily, the IP address stayed the same, so I had no delay in DNS. DOCSIS signal noise ratio is now…
, 2 min read
I wrote about hosting static sites on various platforms: Hosting Static Content with surge.sh Hosting Static Content with now.sh, now.sh renamed themself to vercel.app Hosting Static Content with netlify.app Hosting Static Content with Cloudflare Hosting Static Content with Neocities Hosting…
, 7 min read
Our solar system is not stable when considerung time ranges of several Gigayears. These are the results of simulations done by Laskar and Gastineau. 1. Nomenclature Notions for ellipses, see below figure: center M semi-minor axis b semi-major axis a (linear) eccentricity e, numerical eccentricity…
, 2 min read
XHProf is a PHP profiler. I had written on XHProf here: Profiling PHP Programs Profiling PHP Programs #2 XHProf was originally written by Facebook engineers. Even though it severely slows down your PHP program during execution, it is nevertheless a valuable tool to get an understanding, where…
, 36 min read
Authors: Roman Edenhofer and Simon Apers Université Paris Cité, CNRS, IRIF, Paris, France Abstract 1. Introduction and summary Counting few paths Unambiguity, Fewness and a language in $\mathsf{BQL}$ (maybe) not in $\mathsf{BPL}$ Conclusion and open questions 2. Space-bounded computation 2.1…
, 6 min read
SSHGuard is a software to block unwanted SSH login attempts. SSHGuard has a very remarkable architecture: it has a set of independent programs doing parsing, block-indication, and actual blocking. I wrote about this in Analysis And Usage of SSHGuard. SSHGuard 2.4.3 is about 100kLines of C and shell…
, 2 min read
1. The post Hosting Static Content with GitLab was mentioned on Hacker News and this site experienced a heavy increase in accesses. Neither PHP, nor NGINX, nor the ISP experienced any problems. Nevertheless, I had never before seen such a stark rise in accesses to this website with real…
, 15 min read
1. Notation 2. Example Runge-Kutta methods 3. Local discretization error 4. Order condition 5. Power series expansion for global error 6. Cauchy product formula 7. Recursive calculation of the order condition Below text is based on the results in Peter Albrecht: "A New Theoretical Approach…
, 2 min read
I wrote about hosting static sites on various platforms: Hosting Static Content with surge.sh Hosting Static Content with now.sh, now.sh renamed themself to vercel.app Hosting Static Content with netlify.app Hosting Static Content with Cloudflare Hosting Static Content with Neocities Hosting…
, 2 min read
I wrote about hosting static sites on various platforms: Hosting Static Content with surge.sh Hosting Static Content with now.sh, now.sh renamed themself to vercel.app Hosting Static Content with netlify.app Hosting Static Content with Cloudflare Hosting Static Content with Neocities GitLab…
, 58 min read
1. Konsistenz, Konsistenzordnung und Fehlerkonstanten 2. Die Anwendung linearer Mehrschrittverfahren bei DAE 3. Mehrere Charakterisierungen der Konsistenzordnung 4. Die erste Dahlquist-Barriere 5. Die zweite Dahlquist-Barriere 6. Annullierte Dominanz und Totalannullation 7. Das $n$-dimensionale…
, 17 min read
1. Semistabilitätsfunktionale in Matrixdarstellung 2. Bemerkungen zum Spijkerschen Stabilitätsfunktional 1. Semistabilitätsfunktionale in Matrixdarstellung Mit Ausnahme der Booleschen Algebra wird keine Theorie in der Mathematik universeller benutzt als die lineare Algeba. Es gibt kaum eine…
, 19 min read
1. Das modifizierte Newton-Verfahren und Spezialisierungen 2. Die Divergenzsätze von Hughes Hallett 3. Die Experimente von Byrne/Hindmarsh/Jackson/Brown Einer der ganz zentralen Bestandteile eines Programmes, basierend auf Verfahren mit impliziten Stufen, ist die Auflösung der…
, 58 min read
1. Einführung und grundlegende Begriffe 2. Die Lemmata von Gronwall 3. Notation und Darstellungssatz für Differenzengleichungen 4. Stabilitätsfunktionale für feste Schrittweiten 5. Projektorstabilitätsfunktionale 6. Nichtäquidistante Gitter 7. Die Eigenwerte gewisser tridiagonaler…
, 23 min read
1. Konditionszahlen von Matrizen 2. Elementare Zeilen- und Spaltenoperationen 3. Die $LU$-Zerlegung 4. Die Gauß-Elimination Bei jedem Iterationsschritt eines Newton-Raphson-Verfahrens, bzw. bei jeder Aktualisierung der Iterationsmatrix beim Newton-Kantorovich Iterationsverfahren, fällt die…
, 6 min read
1. Projektor Sei eine lineare Mannigfaltigkeit ${\cal M}\subseteq\mathbb{C}^n$ aufgespannt durch die $s$ linear unabhängigen Vektoren $a_1,\ldots,a_s\in\mathbb{C}^n$. Sei $A=(a_1,\ldots,a_s)\in\mathbb{C}^{n\times s}$. Es gilt $$ % Mehrfache Indizes für Minoren: % #1: Anzahl der Indizes, #2:…