Welcome

This is my home in the virtual world, where I write about things that I want to share. The freely available software that I've written as well as some of the photographs I've taken over the years can also be found here. Please use the navigation links on the right if you are looking for something.

Recent articles

1. Resonance frequency of a composite tube

   Based on a question I ran into at work, I wanted to explore the influence of parameters like cross-section, wall thickness and laminate lay-up on the resonance frequency of a carbon fiber composite tube.

   The goal of this exercise is to determine which of the parameters are dominant.

2. Using sed

   As I’ve written about before (see engineering), I often use CalculiX for structural mechanics calculations of products made from composites. These often involve calculating lots of different combinations of materials, lay-ups and load cases. For convenience and for them being self-contained, each variant is usually in a different directory.

   So when I find an improvement to e.g. a pre.fbd, Makefile or job.inp, I want modify all of the other instances as well. This is where sed (which stands for “stream editor”) comes into play.

3. Zero DSR power consumption

   Based on the data from the dashboard I’ve created a graph of the power consumption for a 2020 Zero DSR.

   As far as possible, this was measured on a level road at constant speed, on a good road surface and without much wind. The power is the product of the speed in km/h and the energy usage in Wh/km.

4. Use pygmentize as a colorized cat

   The less command uses a programmable filter with which you can colorize its output. In this article an alias to do the same for cat is shown.

5. Gnumeric build fix for FreeBSD

   Problem

   Trying to update gnumeric to version 1.12.50_1, the following errors occurred during installation:

   pkg-static: Unable to …

6. Patching CalculiX Graphics to fix flipped screen hardcopy

   Since some time, I’ve had the problem that generating hardcopy images from cgx doesn’t work properly; the pictures are inverted vertically.

   At first, I thought this might have been a change in cgx. But comparing the source code for cgx.c for 2.16 up to and including 2.19, I don’t see anything that would explain it.

7. Examining an OpenSSH ECDSA public key

   Intrigued by this question, I investigated the structure of an OpenSSH ECDSA public key.

8. Python & standard output redirection on ms-windows

   Redirecting standard output of the Python script on ms-windows can cause strange crashes because of encoding differences.

9. Profiling Python scripts (5): ent_without_numpy

   This is the fifth in a series of articles that covers analyzing and improving performance bottlenecks in Python scripts. The program ent_without_numpy.py is a lot slower than the version that uses numpy. The performance of ent_without_numpy.py is the topic of this article.

10. Profiling Python scripts (4): vecops.indexate

    This is the fourth in a series of articles that covers analyzing and improving performance bottlenecks in Python scripts. The performance of stl2ps is the topic of this article.