inotify-tools: inotifywait

I wanted to see what files and when J-Pilot accesses its pdb and pc3 files. In my case strace produces much more output than actually needed. But inotifywait shows what and when files are accessed.

inotifywait -m .jpilot/

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OpenGL Program: Earth with Moon Rotating around Sun

My other son had a practical training at Fraunhofer IGD. He wrote an OpenGL/C++ program in Windows where one views the earth rotating around the sun, thereby with its rotating moon, see picture below.



I ported this program to Gtk/Linux. You’ll find the code in openglSunEM.c. The link between Gtk and OpenGL is realized by GtkGlExt. On Ubuntu you have to install libgtkglext1-dev.

openglSunEM can either be called with or without textures using command line flag “-t”. Typing ESC stops the program.

The main geometric transformation is handled in drawGLScene(): draw sun, draw earth, draw moon (which rotates around the earth, which in turn rotates around the sun). The speed of rotation can be increased or decreased with the arrow keys (GDK_KEY_Up, GDK_KEY_Down), one can zoom in or out (GDK_KEY_I, GDK_KEY_O).

The whole animation can be rotated like an arcball, its implementation being in ArcBall2.c.

On Differential Forms

A couple of years ago I went through Otto Forster’s Analysis 3 book for self study of differential forms. I thought the presentation could be leaned more towards matrices and determinants, which since Bourbaki’s time got a difficult stand in mathematics.

Here is the document: On Differential Forms.

Once I struggle through QuickLaTex I will try to embed it directly in WordPress.

Number of Combinations for German Tax Id

I was asked by a colleague of mine how many combinations are possible for the German tax id. The German tax id is built entirely from eleven digits. Its specification is given in Pruefziffernberechnung, see Steueridentifikationsnummer in the German Wikipedia. Every person reported to live in Germany is assigned one tax id, even babies and children. 20 years after the death of a person the number can be recycled.

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