, 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…
, 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…
, 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…
, 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…
, 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,…
, 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…
, 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 …
, 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…
, 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…
, 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…
, 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…
, 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…
, 7 min read
1. Statement of the problem. This blog does not offer any newsletter functionality. If a reader is interested to know whether I have posted new content, he must either use an RSS feed or directly visit this site. WordPress offers the possibility of getting notified of new posts automatically. I.e.,…
, 2 min read
1. Satz: Stabilitätskriterium von Routh/Hurwitz, nach Routh, Edward John (1831--1907), Hurwitz, Adolf (1859--1919). Voraussetzungen: Es sei $$ p(z) = a_0z^n + a_1z^{n-1} + \cdots + a_{n-1}z + a_n = a_0 (z - \lambda_1) \ldots (z - \lambda_n) $$ ein beliebiges komplexes Polynom mit…
, 1 min read
Die Formel von Faà di Bruno, Faà di Bruno, Francesco (1825--1888), verallgemeinert die Kettenregel auf die Form für beliebig hohe Ableitungen. 1. Satz: Formel von Faà di Bruno Es hänge $w$ von $u$ ab, $u$ ist hierbei Funktion von $x$. Es sei $D_x^k u$ die $k$-te Ableitung von $u$ nach…
, 6 min read
Aus dem Eindimensionalen sind das Lagrangesche und Schlömilchsche Restglied bekannt. Lagrange, Joseph Louis (1736--1813), Schlömilch, Otto (1823--1901). $$ \eqalignno{ f(x) &= \sum_{k=0}^n {f^{(k)}(a)\over k!}(x-a)^k + {1\over n!}\int_a^x (x-t)^n f^{(n+1)}(t) dt\cr &=…
, 2 min read
Wie differenziert man Determinanten, die von einem Parameter abhängen? 1. Satz: Voraussetzungen: Es seien $a_{ij}(\lambda)$ differenzierbare Funktionen. Es…
, 13 min read
1. Integraldefinition 1. Sei $f$ eine geeignet gewählte holomorphe Funktion. Dann definiert man für eine quadratische Matrix $A$ die Matrixfunktion $f(A)$ zu $$ f(A) := {1\over2\pi i}\int_\Gamma f(\lambda) (I\lambda-A)^{-1} d\lambda. $$ Wegen dem Satz von Cauchy, Cauchy, Augustin Louis…
, 7 min read
Die Eigenwerte einer Matrix hängen stetig von den Komponenten der Matrix ab. Dies soll hier bewiesen werden. Man kann sogar noch weitere Abhängigkeitssätze beweisen, jedoch werden die Begründungen dann länger, siehe das Buch von Gohberg/Lancaster/Rodman (1982), Autoren sind Gohberg, Izrael'…
, 6 min read
1. Die Spur (engl./franz.: trace) einer Matrix $A\in\mathbb{C}^{n\times n}$ ist definiert zu $\def\tr{\mathop{\rm tr}}\tr A=a_{11}+\cdots+a_{nn}$, somit die Summe der Hauptdiagonalelemente. Durch elementare Rechnung zeigt man $\tr AB=\tr BA$, für zwei beliebige Matrizen $A\in\mathbb{C}^{n\times…