Diagonal of Squared Jacobian

25th July 2021

Assume \(f\) is a \(m\)-vector valued function in \(n\)-variables, i.e., \(f:U\subseteq\mathbb{R}^n\to\mathbb{R}^m\). The Jacobian is given by $$ J = \begin{pmatrix} f_{x_1}^{(1)} & \cdots & f_{x_n}^{(1)} \\ \vdots & \ddots & \vdots \\ f_{x_1}^{(m)} & \cdots &…

Hashnode Markdown Bulk Import Is Troublesome

24th July 2021

1. I have written more than 300 blog posts, see sitemap. I wanted to import them into Hashnode. As all these posts were already in Markdown format, it was obvious to use the "bulk import" feature in Hashnode. The Hashnode bulk import reads a zip-file. This zip-file contains individual…

Performance Comparison C vs. Java vs. Javascript vs. LuaJIT vs. PyPy vs. PHP vs. Python vs. Perl

13th July 2021

1. Introduction. I always wanted to benchmark PHP, to confirm myself that choosing PHP as a static site generator is not a dead-end, compared, for example, against node.js. PHP 7 has already made huge performance advancements. See PHP 7: Features and Performance Comparison: Drupal - Compared to…

Calling MD4C from PHP via FFI

11th July 2021

1. Problem statement. When using one of the static site generators an important part of all of them is to convert Markdown to HTML. In my case I use Saaze, and I measured roughly 60% of the overall runtime is used for converting Markdown to HTML. I have written on Saaze here and here. When…

Brave Browser SIGSEGV Crash

29th June 2021

Today I saw a SIGSEGV error when fetching data from Twitter: After reloading the page the error was gone. I hadn't seen this kind of error before. Version used: Brave 1.25.73, Chromium: 91.0.4472.106 (Official Build) (64-bit). Revision…

Deletion Troublesome in Hashnode.com

27th June 2021

Before I moved away my blog from WordPress.com to this place, I checked whether another provider would fit my needs. See for example surge.sh, vercel.app, or netlify.app. I also looked at Hashnode.com. I liked Hashnode as it provides Markdown as input. I later learned that Hashnode also provided…

WordPress.com Bulk Update

21st June 2021

I wanted to redirect Google search results from WordPress.com to this blog. Ideally, one would add a "canonical link" in the head-tag of the HTML code. See for example stitcher.io: 07 — Be Searchable: <head> . . . <link rel="canonical"…

Ampersands in Markdown URLs

13th June 2021

In this blog I reference web-page- or image-URLs, which contain ampersands ("&"). For example, https://www.amazon.com/s?k=Richard+Stevens&ref=nb_sb_noss. Unfortunately, Markdown as specified by John Gruber does not allow this. This can be checked with John Gruber's…

Using NUC as WLAN Router

5th June 2021

I had already written about setting up an Odroid as IP router: Using Odroid as IP router. Today I powered down my second Odroid, which I had previously used as WLAN router. There was nothing wrong with the Odroid. It just drew 7W and the NUC was already running next to the Odroid. So there was no…

Matomo with Hiawatha

3rd June 2021

For this blog I use the Hiawatha web-server. I wanted to employ a web-analysis tool. For this I chose Matomo. Matomo was called Piwik previously. I already use GoAccess on which I have written in Using GoAccess with Hiawatha Web-Server. To use Matomo with Hiawatha I had to do the following: Unzip…

Generate RSS from Markdown

30th May 2021

For this blog I wanted an RSS feed. Saaze by default does not provide this functionality. Saaze is supposed to be "stupidly simple" by design, which I consider a plus. Luckily, generating an RSS feed is simple. It contains a header with some fixed XML. Then each post, is printed as so…

Configure Lighttpd With PHP and HTTPS

29th May 2021

I use the Hiawatha web-server on my servers. For example, this blog runs on Hiawatha. Recently I needed a web-server on Red Hat Enterprise. Unfortunately, Red Hat does not provide Hiawatha directly on its Satellite program, but Lighttpd was there. I also wanted to use PHP and the connection should…

Speed-Tests With Pingdom.com

23rd May 2021

As I have moved my blog from WordPress to eklausmeier.goip.de, I wanted to know if I am really getting better response times across the globe. WordPress always felt slow. Below measurements will confirm this. Pingdom.com is a monitoring and performance measurement website. See Wiki article. Let's…

Using GoAccess with Hiawatha Web-Server

22nd May 2021

GoAccess is a remarkable analyzer for your log-files written by the web-server. For example, GoAccess can read and analyze the log-files from Apache web-server. In the same vein, after some configuration, it can also read and analyze the log-files from Hiawatha web-server. The Hiawatha web-server…

Moved Blog To eklausmeier.goip.de

18th May 2021

The blog eklausmeier.wordpress.com is no longer maintained. I moved to eklausmeier.goip.de, i.e., this one. During migration I corrected a couple of minor typos and dead links. Main reasons for the move: This new WordPress editor put the last nail in the coffin, existing content is garbled once…

PHP extension seg-faulting

29th March 2021

Task at hand: Call Cobol (=GnuCOBOL) from PHP. I used FFI for this: <?php $cbl = FFI::cdef("int phpsqrt(void); void cob_init_nomain(int,char**); int cob_tidy(void);", "/srv/http/phpsqrt.so"); $ffj0 = FFI::cdef("double j0(double);",…

Add Disjoint IP Addresses To SSHGuard Blacklist

15th March 2021

Problem at hand: There are multiple machines running SSHGuard. Each of these machines accumulates different sets of blacklists. Task: Add disjoint IP addresses from one machine to another machine's blacklist. 1. Copy from "master" machine: scp -p master:/var/db/sshguard/blacklist.db…

Lesser Known Static Site Generators

7th March 2021

Well known static site generators are Hugo (written in Go), Pelican (written in Python), Grav (written in PHP), or Eleventy (written in JavaScript). For a list of static site generators see Jamstack (322 generators listed) or Static Site Generators (460 generators listed). The following three…

Testing J-Pilot feature-gtk3 branch

2nd March 2021

J-Pilot 1.8 still relies on GTK+ 2, which is heading towards planned deprecation. The entire work to migrate to GTK+ 3 is done by volunteers, Judd Montgomery and David Malia. This post is about testing this new experimental branch feature-gtk3 from GitHub. Installing this branch is…

Analysis And Usage of SSHGuard

28th February 2021

To ban annoying ssh access to your Linux box you can use fail2ban. Or, alternatively, you can use SSHGuard. SSHGuard's installed size is 1.3 MB on Arch Linux. Its source code, including all C-files, headers, manuals, configuration, and makefiles is 8 KLines. In contrast, for fail2ban just the…

ssh as SOCKS server

21st February 2021

Assume three computers A, B, and C. A can connect to B via ssh, but A cannot connect to C, but B can connect to C. A -> B -> C On A open ssh as SOCKS-server with ssh -N -D 9020 user@B Now on A one can use brave --proxy-server="socks5://localhost:9020" The browser will then show…

Poisson Log-Normal Distributed Random Numbers

9th February 2021

Task at hand: Generate random numbers which follow a lognormal distribution, but this drawing is governed by a Poisson distribution. I.e., the Poisson distribution governs how many lognormal random values are drawn. Input to the program are \(\lambda\) of the Poisson distribution, modal value and…

Performance comparison Ryzen vs. Intel vs. Bulldozer vs. ARM

1st February 2021

For comparing different machines I invert the Hilbert matrix $$ H = \left(\begin{array}{ccccc} 1 & {1\over2} & {1\over3} & \cdots & {1\over n} \\ {1\over2} & {1\over3} & {1\over4} & \cdots & {1\over n+1} \\ {1\over3} &…

dumpe2fs: When was my hard-drive first formatted?

23rd January 2021

I repeatedly forget to remember when my hard-drive or SSD was first formatted. Command for this is dumpe2fs. This command is part of package e2fsprogs. Example: # dumpe2fs -h /dev/sda1 dumpe2fs 1.45.6 (20-Mar-2020) Filesystem volume name: <none> Last mounted on: /boot Filesystem…

Unitymedia und SIP VoIP

16th January 2021

Folgendes schrieb ich an die Firma Unitymedia, jetzt Vodafone: Ich möchte gerne meine Rufnummer XXX über meine YYY Telefonanlage via VoIP betreiben. Ich verwende den von Ihnen bereitgestellten Router "Vodafone Station". Meine Kundennummer lautet ZZZ. Ich benötige nun folgende sieben…

Compiling Java source to binary (native)

19th December 2020

With GraalVM you can now fully compile a Java file to a native binary. This is also called AOT, ahead-of-time compilation. Compilation is very slow, and resulting binary is huge as it must contain all code which might be referenced. In contrast the class file usually is quite small. Though, it is…

Windows 10 very slow after reboot

13th November 2020

I repeatedly noticed that my Microsoft Windows 10 laptop is noticeably slow when restarted. This time I rebooted the laptop and just watched what happened in task manager. Below are the results. Waiting for more than 10 minutes doing nothing: one third of the machine is loaded with managing its…

Statistics of this Blog: Crossed 110.000 Views

7th October 2020

This blog was viewed more than 110.000 times since its inception and had more than 84.500 visitors. The averages per month are: The most popular posts this year are: The most popular posts over all years are: Distribution of countries accessing this blog over last 365 days, USA is number one,…

Configure boot settings in UEFI

29th August 2020

Main source for trouble-shooting is Arch-Wiki UEFI. It describes the commands: bcfg within UEFI shell Linux command efibootmgr 1. Highly recommended to install the UEFI-shell, which is in package edk2-shell. On Asrock copy cp -p /usr/share/edk2-shell/x64/Shell_Full.efi /boot/shellx64.efi So name…

SSD Speed on Dell XPS 13 9350 with Samsung EVO 970 Plus

9th August 2020

In continuation of blog-post SSD Speed on Dell XPS 13 9350, here are performance measurements for a Samsung EVO 970 Plus in Dell XPS 13. Caveat from Dell xps 13 9350 and Samsung 970 evo M.2 nvme Compatability?: However, be aware that although the XPS 13 9350 uses a PCIe x4 configuration for its…

← Older       Newer →