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I write, therefore I am

With this variation on a famous statement by the philosopher Descartes, I would like to express that the act of writing about what happens in my life is important to me.

Friday, January 27, 2023


Thursday, January 26, 2023

Museum No Hero

Conny and I went to Museum No Hero where we saw two exhibitions. First we saw the exibition Oog in Oog met de Wereld (Eye to Eye with the World). The works that I found noteworthy (all of them, if I am not mistaken): From the exhibition Verzamelen is kleur bekenen. De wilde collectie van Geert Steinmeijer (Collecting is showing your true colours. The wild collection of Geert Steinmeijer), I found the following works noteworthy.

Afterwards, we walked towards Twickel Castle and around the area. The castle now belongs to a foundation that owns large areas of land around the city Delden.

Tuesday, January 24, 2023

Fairy ring

I found a fairy ring in the back garden of our house. It is actually inside an old doormat.


Sunday, January 22, 2023


Today is the first day of the year 4720, the year of the rabbit according to the Chinese calendar. The spring festival has begun.

Speck of snow

When we went walking this afternoon, there were some speck of snow falling from the sky, non of which stayed on the ground. On Friday, there was some substantial snow in the Southern parts of the country but nothing in our part of the country.

Small area substitution patterns

In the past weeks, I continued working on the program for find substitution patterns for irregular grids of squares and equilateral triangles. Below it shows 53 of the 15407 patterns with a boundary length of 27 that the program found, starting with the pattern with the smallest area. As can be seen, many of these patterns can be split in more than one smaller pattern. I have wondered whether I should exclude these combinations in the counts, but it should be noted that there are restriction on how substiturion patterns can touch each other. The program does check if the outside of the boundary can be filled with squares and triangles. It does this by checking if the coves can be filled. The count of substitution patterns per length of the boundary, starting with a length of 12, is: 1, 0, 1, 1, 4, 3, 12, 15, 44, 75, 200, 411, 1070, 2420, 6304, 15407, 40569. I have not found this sequence in The On-Line Encyclopedia of Integer Sequences®.

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Saturday, January 21, 2023

Underneath the wings of a butterfly

This afternoon, I visited the exhibition Underneath the wings of a butterfly at TETEM art space. I only saw the augmented reality part of the exhibition where you had to walk around the room with a tablet to which headphone were attached. You had to follow a butterfly. Interesting concept. There were a lot of flat photographs in the scenery. I did not wait for the virtual reality part of the exhibition.

Friday, January 20, 2023

Mystery machine code

Yesterday, the source code of The Lisa was released. See: The Lisa: Apple's Most Influential Failure. I looked around the website of Computer History Museum and came across: The Earliest Unix Code: An Anniversary Source Code Release, which is about Unix Book II from the papers of Dennis Ritchie, which contains almost 190 pages of printed source code listings, written in PDP-7 assembly code. It states that page 145-169 contain an unidentified program, perhaps an interpreter for a programming language? B? I did glance at the code, but I wonder if it is an interpreter for the B language. The instruction set is described in PDP-7 Reference Manual. Based on the description, it should be possible to write a small interpretter that could process the assembly listings.


Thursday, January 19, 2023

Avatar: The Way of Water

This evening, Conny and I went to see the movie Avatar: The Way of Water. It is an impressive movie and a good sequal with an open end to further sequals. Good balance between action and drama. Also some interesting additions to the flora and fauna of Pandora, especially, the introduction of the Tulkun, a sentinent race of whale like animals.

Friday, January 13, 2023


Wednesday, January 11, 2023

B93 Anno Nu

I went to see the opening of the exhibition B93 Anno Nu at the artist collective B93. It has been a long time I went there. The last time was on Wednesday, March 4, 2020. The exhibition had works by:


Tuesday, January 10, 2023

Polygon triangulation demo

Today, I developed a demo for a simple polygon triangulation algorithm. I developed it for a presentation I want to give. It implements a sweep line algorithm. The Clipper2 - Polygon Clipping and Offsetting Library for Boolean operations on polygons also makes use of a line sweep algorithm, but the problem is a bit more complicated as there are more kinds of events that one has to deal with.

Monday, January 9, 2023


At 17:36:49, I bought the book Historische atlas NL: Hoe Nederland zichzelf bijeen heeft geraapt written by Martin Berendse and Paul Brood in Dutch and published by Wbooks on Monday, September 2, 2019, ISBN:9789462583177, from bookshop Broekhuis for € 20.00.

Sunday, January 8, 2023

Substitution patterns

I wrote the program irst_sub.cpp to find substitution patterns for irregular grids of squares and equilateral triangles. The program implements the ideas I expressed last week, which generates all boundaries that can be filled with at least two alternating patters. I wrote some code to visualize the solutions. While studying, I found another alternative coupling. It looks similar like one of the two I found before. It is shown below:

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Saturday, January 7, 2023

The life of a software engineer

I came across the interesting blog Things they didn't teach you about Software Engineering, which I think described the reality of software engineering quite well. In the past years, I discovered that my greatest struggle with software engineering is my deep rooted sense of insecurity. Software engineering is a rather demanding task. I think it is one of the more creative types of engineering, where the product of the engineering is not the design for a system, but where the product is the system itself in the form of code. Furthermore, there are usually many different solutions for a problem and many different ways to express those solutions in code. With software engineering there are often also many single points of failure. You have to live with the reality of bugs that can express themselves in the most unexpected ways. Professional software engineering is usually done in teams where you have to work together with others on a single code base and where it is common that your colleagues review you code or at least come across it when they have to implement some feature or fix a bug. I often find myself worrying a lot whether the solution I have chosen is the right one or whether I have tested it enough. It is a common experience that you think you have tested all cases just to discover that you missed some. Either you learn to hide your insecurities or they drive you on a road to soul searching, possibly resulting in various forms of burn-outs, in alienation from your family and friends outside of you work circle, in changing your world view and/or in losing your faith. But which might in the end result in a form of enlightenment.

Kunst en Koffie

At Concordia, I saw the exhibition Kunst en Koffie with art works (mainly prints) from their art lending collection. There was also a price list for items that you could buy. Some of the works that I found most interesting, drawings or paintings from houses on a water front, where not in the price list.

Tuesday, January 3, 2023

Boundary of subsitution patterns

I have been thinking about boundaries of subsitution patterns for irregular grids of squares and equilateral triangle. If there are two irregular grids that are the same except for some changes in a closed area such that there is a single boundary where on the inside the grids are different while on the outside is the same, then this boundary has certain properties. The corners on the inside of this boundary cannot be smaller than 150°, because otherwise it is not possible to fill it in more than one way and is it thus not possible that it is on the inside of an area that can be filled in more than one way. For a corner with an angle of 150° one of the sides is touched by a triangle and the other by a square. For a corner with an angle of 180° in one alternative both sides have are touched by a triangle while in the other they are touched by a square. For a corner with an angle of 210° the same holds as with an angle of 150°. For corners with angles of 240° and 300° it is possible that in the alternatives the sides are touched by the same shape or by different shapes. Corners with an angle of 330° is not possible, because the corner on the outside is too small to fit anything. There are some more restrictions on angles of consecutive corners due to the shapes on the outside. I think it is possible to write a program that generates all possible boundaries, with increasing area, and see if they can be filled with at least two different patterns, such that the shapes on the inside are different. This could start with assigning different assignments of triangles and squares on the inside of the boundary and see if with this assignment the area on the inside can be filled.

Algol 68

I read some post on Hacker News about Algol 68 Genie. That reminded me that in my first year at the university we had to write programs in Algol 68. I also (vaguely) remember some story that the compiler that had some bug that caused it malfunction on some programs during a few months of the year and that instructors told students to wait a month and try again. This was probably not the Algol 68 compiler developed by the Dutch branch of Control Data Corporation and released in 1974. According to A Shorter History of Algol68 in which it says: "Zoethout ea, CDC Netherlands 1974. Full implementation, used mainly in teaching in Germany and the Netherlands on CDC mainframes". The report describing the compiler is: Algol 68, Version I, Reference Manual. The document describing the development of this compiler An early implementation of revised algol 68 makes mentions of the CDC 6000 series. According to the document Informatica aan de THT, fase 01, 1974 - 1981, this compiler was used at the university (then still called 'Technische Hogeschool Twente'), but I remember that we worked on a DEC 10 mainframe that was installed in 1975. The report A History of Algol 68 mentions Algol 68C, a portable compiler that also made available for the DEC-20 mainframes. Also A brief history of Algol 68 Genie makes mentions of the Algol 68C compiler on the DECsystems 10. I have a book by Cornelis H.A. Koster, Th.A. Zoethout, and H. Meijer, Systematisch programmeren in Algol 68, published in 1978, about systematic programming in Algol 68.

Sunday, January 1, 2023

15.7° Celsius

At the start of the night, the temperature at Twenthe Airport has gone up to 15.7° Celsius, which breaks last years record of 13.5° on this date.

Saturday, December 31, 2022

16.2° Celsius

Just like last year, we will end the year with another weather record. The temperature at Twenthe Airport has gone up to 16.2° Celsius, which breaks the last years record of 13.8° and is also a bit higher than the predicted maximum temperature of 15.9°. Last night the temperature did not drop below 11.1°, which is not really a record, because last year the temperature did not drop below 13.0° during the night, but nevertheless this is still above the average highest temperature for this time of the year.

Friday, December 30, 2022

Rijksmuseum Twenthe

This morning, Conny and I visited Rijksmuseum Twenthe. We went there to see The Standard Bearer by Rembrandt, which our government bought for €175 million from the Rothschild family earlier this year and that has been on tour through museums in the Netherlands. This month it was on display here in Enschede.

In the room where The Standart Bearer was on display, there were a number of works by Nour-Eddine Jarram on display, which were inspirted by the painting. (See also Rembrandt meets Nour.) The ones I found notable:

We walked through the museum and seeing the same exhibitions as when we visited the musuem in November. I found the following works notable:


Thursday, December 29, 2022

Shots of Dune 2021

For my page on Dune 2021 film, I was searching for a list of all shots. I found two images with all the shots: 1938 shots of Dune 2021 enjoy! 8K edition and DUNE - all 2331 individual shots. I discovered it is not easy to display just a part of an image using HTML and CSS. It is relatively easy with JavaScript. I wrote some JavaScript with which the shots from the two images can be compared. You have to provide the URLs for the images, preferable after you have downloaded them, because they are rather large. Pressing the bottom 'next' button causes both shots incremented and the numbers added to the output field. I discovered that they do not really match. So, the actual number of shots might be higher than 2331.

URL for 1939 shots:

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URL for 2331 shots:

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Tuesday, December 27, 2022


Sunday, December 25, 2022

Advance of Code

I woke up early this morning and shortly after six in the morning, I went downstairs to get my laptop. The Advent of Code puzzle was not so complicated for someone who has had an interest in parsing for a long time. I finished it in a little more than half an hour and then spend some time writing some notes about how I arrived at my solution. I was the 1407th person to finish this years Advent of Code.


Saturday, December 24, 2022

Theo van Doesburg

I paged through the book Theo van Doesburg: oeuvre catalogus about the works of Theo van Doesburg. I noticed that a number of his pattern resembled Street Tile Patterns in the sense that they do not contain point where four tiles touch but only T-like crossings. The patterns I found are: I searched if the manifestos mentioned in the book 100 Artists' Manifestos to which he contributed could also be found amongh his writing mentioned in the book, but did not find them.

Tuesday, December 20, 2022


Monday, December 19, 2022


Sunday, December 18, 2022

Advent of Code

Todays puzzle of Advent of Code was relatively easy compare to those of the last two days, which both took me some considerable amount of time. This year, I did not attempt to solve the puzzles as fast as possible. Several times, I have come up with good ideas while being away from the screen, like yesterday evening, when I came up with the solution for the second part of the puzzle while bring Andy back to his place, about a half hour drive in one way direction. Today, I also made some small improvements to MarkDownC and I discovered that using '&&' on the command line causes the following program only to be executed when the previous did not return an error. Now I am using the following command line to process a single MarkDown file for a day:
MarkDownC Day18.md >p.c; gcc -Wall -g p.c -o p && ./p
This will run the MarkDownC on the input file Day18.md into the file p.c. If MarkDownC found a parsing error, that error will be written in a unterminated comment. The C compiler will report this and show the line telling where the error is. When the C compiler finds errors in the program it will return with an error status. And finally, when there is no error, the program will be executed.

Sol_HSA has some interesting animations for the puzzles.

The snow that fell Friday morning, has not melted away yet. This night the temperature at Twenthe Airport dropped to -9.4° Celcius. The coldest temperature on record for this day is -11.9° Celcius.

Alternative couplings

This afternoon, I went through some combinations of regular grids of squares and equilateral triangle and I found two interesting patterns which connect four elementary triangles without containing those themselves. They are shown below. The elementary triangles are marked with yellow. Some black triangles are shown to display the fixed border. Also the top and bottom (center) points are fixed.

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I am also thinking about a program which systematically searches combination of regular patters for additional patterns.

Saturday, December 17, 2022


Friday, December 16, 2022


In the morning, there was about 2cm of snow. It has been rather cold the last days, so it is not surprising that it is not wet snow. The snow stayed during the day, because the temperature, according to the weather station at Twenthe Airport, did not get above 0° Celcius.

Thursday, December 15, 2022

Enschede Lights Up

Conny and I went into the city to have a dinner at an Indonesian restaurant. After this we walked to Tourist Info Enschede for a guide for the Enschede Lights Up event. We also were given two glow sticks. We saw the following light works: We also visited bookshop Broekhuis about half way to warm up a bit, because the temperature was about -3° Celsius.

Christmas LEDs

This afternoon, I reprogrammed the the LED strip for Ugly Christmas Sweater Day tomorrow with the ChristmasLEDS.ino program, which shows red and green colours with some white flashes.

Wednesday, December 14, 2022


January 2023
December 2022
November 2022
October 2022
September 2022
August 2022
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The Art of Programming
eXtreme Programming


Hamilton cycles
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Califlower fractal




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