Konvergenzresultate für feste Schrittweiten

, 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…

Lösung linearer Gleichungssysteme

, 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…

Projektionsmatrix eines Raumes

, 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:…

Turning 60 - Now What?

, 2 min read

I turned 60 this year. I had written a similar post ten years ago: Turning 50 - Now what? What has happened in the last ten years? The last time I wrote: I am married and have three children. All three children show interest in society and technology, and will likely find their way through life.…

Dark Mode on Website

, 6 min read

This blog offered to switch betwen light and dark mode. But this choice was not stored anywhere. So any page you clicked on, you had to choose dark mode again. Now I store this choice in localStorage on the client. While cookies could also be used for storing this choice, they are not needed for…

IGYRC5108-U: IBM Cobol Compiler Terminating

, 1 min read

I stumbled on below error message from the IBM COBOL compiler for mainframe: IGYRC5108-U COBOL COMPILER TERMINATING: UNCORRECTABLE PROGRAM INTERRUPT CONDITION. The COBOL program was not fully compiled but compilation stopped midway. Further messages from the compile run: PROGRAM CHECK,…

Member of 1MB club

, 1 min read

I am now a member of the 1MB club. The members must have websites with size below 1 MB. This new membership is not surprising as I am already a member of the two clubs: Member of 512KB club Member of 250KB club This 1MB club has 781 members as of today. Becoming member there is by using: git…

Performance Comparison of Wendt Website: WordPress vs. Simplified Saaze

, 4 min read

In the previous post Example Theme for Simplified Saaze: Wendt I demonstrated the transition from a website using WordPress to Simplified Saaze. This very blog, which you are reading right now, also uses Simplified Saaze. his post shows how much better performance-wise this transition was. The…

Example Theme for Simplified Saaze: Wendt

, 12 min read

Another theme for Simplified Saaze called "Wendt". You can inspect it here. It offers below features: Responsive with media breaks for large and small screens, and for printing. Top menu with submenus. Two column using CSS grid, "Holy Grail Layout". Multiple blogs: Each…

Converting UNIX Timestamps to Year, Month, Day in COBOL

, 5 min read

1. Task at hand. COBOL programs reads UNIX timestamps as input. Output should be the values of year, month, day, hour, minutes, seconds. In C this is just gmtime(). gmtime accepts time_t and produces struct tm: struct tm *gmtime(const time_t *timep); On mainframe, however, it is sometimes a little…

Installing and Configuring the H2O Web-Server

, 7 min read

1. Task at hand. Install H2O web-server on Arch Linux. H2O is a web-server written by Kazuho Oku et al. It supports: HTTP/1 and HTTP/1.1, HTTP/2, HTTP/3 ("QUIC"), FastCGI, therefore PHP-FPM, Reverse proxy, Builtin mruby, though, that crashes. In benchmarks it ranks at the top…

Location of core files in Arch Linux

, 2 min read

In the old UNIX days the core file was written where the offending program was started. The only prerequisite was that there was no limit imposed. Limits can be checked by $ ulimit -a -t: cpu time (seconds) unlimited -f: file size (blocks) unlimited -d: data seg size…

CSS Naked Day

, 4 min read

9th April is CSS Naked Day. A day where you do not use CSS on your web-site. In 2024 I participate in this day, i.e., I will deactivate the CSS on this blog. From the CSS Naked Day: The idea behind CSS Naked Day is to promote web standards. Plain and simple. This includes proper use of HTML,…

Is Binary Compiled with Frame Pointer Support?

, 2 min read

How can you detect whether a Linux binary was compiled with gcc -fomit-frame-pointer Unfortunately the ELF itself does not contain a flag, which tells you that. But looking at the assembler code can give you the answer. First disassemble the code with objdump -d Check the disassembly for below…

Chinese Hackers #2

, 2 min read

In the year 2020 in the blog post Chinese Hackers I noticed that China tries the most to hack my Linux machines. These attempts look like this: $ lastb a ssh:notty 209.97.163.130 Tue Mar 5 13:07 - 13:07 (00:00) sftpuser ssh:notty 93.123.39.2 Tue Mar 5 13:05 - 13:05 …

Installing IBM COBOL for Linux on Arch Linux #2

, 5 min read

I tried to install IBM COBOL for Linux multiple times. I tried to install it on Arch Linux, which is the Linux I use: Installing IBM COBOL for Linux on Arch Linux in 2021 Testing COBOLworx gcc-cobol #2 in 2023 Initially I succeeded in installing the IBM compiler in 2021. The IBM compiler compared…

Parallelizing the Output of Simplified Saaze

, 6 min read

This blog uses Simplified Saaze as its static site generator. Generating all 561 HTML pages takes 0.25 seconds. The environment used is as in below table. Type Value CPU AMD Ryzen 7 5700G RAM 64 GB OS Arch Linux 6.7.6-arch1-1 #1 SMP PREEMPT_DYNAMIC PHP PHP 8.3.3 (cli) PHP with…

GitHub RSS Atom Feeds

, 1 min read

Ronalds Vilcins, in his article RSS feeds for your Github releases, tags and activity, provides a handy overview of some GitHub RSS feeds. I reproduce them here…

MD4C PHP Extension

, 7 min read

This blog uses MD4C to convert Markdown to HTML. So far I used PHP:FFI to link PHP with the MD4C C library. PHP:FFI is "Foreign Function Interface" in PHP and allows to call C functions from PHP without writing a PHP extension. Using FFI is very easy. Previous profiling measurements with…

Let's Encrypt Certbot Usage with NGINX

, 1 min read

Previously I used lefh to generate and update Let's Encrypt certificates for the Hiawatha webserver. Unfortunately, this PHP script no longer works. Therefore I installed certbot: pacman -S certbot-nginx Updating my domains is like this: certbot --nginx -d…