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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.

Monday, August 3, 2020

Marke stones

Conny and I made a biking trip of about 32Km along some marke stones on the South and West borders of the Enschede township. These are the marke stones/poles we visited:
  • At 10:50, the Leppinkpaal
  • At 11:00, the Kattenstaartpaal
  • At 11:56, the Grevenpaal
  • At 12:52, the Hogeveldpaal
  • At 13:11, the Belderspaal
  • At 14:07, the Zandboerpaal
We searched for the Fabelhuttesteen, but did not find it, not knowing the exact location. At home we discovered that we must af approached it within less than 10 meters.

Sunday, August 2, 2020

Round Goki puzzle

I have written a program to analyze the round Goki puzzle that I bought last Wednesday. The program can be used to generate an Exact Cover, to compress the resulting solutions and has some options to analyze the results. There are but a limited number of ways the pieces around the central round piece can be placed not taking into account rotations and mirroring. If we furthermore ignore the colouring of the pieces, but only look to the layout, there are 1,789,051 unique solutions. This is much more than I had expected when I bought the puzzle. To structure the solutions, one can look at the number of possible outer contours when adding pieces from the center. I have sorted the pieces from the center to the outside, first by the first circular layer they occur in, next on the number of circular layers they cover, and next on the number of radial sectors they cover. Below the list of number of countours by selected number of pieces (where all pieces with the same shape but a different colour are counted as one): 1, 2, 5, 5, 28, 13, 13, 26, 12, 30, 55, 55, 588, 1202, 402, 236, 20, 4, 1, and 1 (obviously). I also looked at the correlation between the positions of inner and outer pieces with respect their occurences in the solutions, and it seems there are no strong correlations.

Wednesday, July 29, 2020

Drents Museum

Conny and I went to the Drenthe province. We first went to Drents Museum in Assen, the capital of Drenthe. There we saw several exhibitions. First the exhibition Barbizon of the North: The Discovery of the Drenthe Landscape 1850-1950. I found the following works notable:
  • Jan van Ravenswaay, Landscape with cattle.
  • Jan van Ravenswaay. View of Assen from Beilerstraat.
  • George Loures Kiers. View of the Vaart in Assen.
  • George Loures Kiers. View of the Brink in Assen.
  • Egbert van Drielst, Drents Landscape, 1807.
  • Albarta Ten Oever, Coach Passangers in Schipholt, 1806.
  • Egbert van Drielst, View of Eext Village, 1810.
  • Cornelis Bijlard, View of a tree and Bushes, 1836.
  • Andreas Gerrit Jacobsen Roelofs, Little shed in Weerdingen, 1859.
  • Willem Roelofs, The Dolmen of Tynaarlo, 1861.
  • Alexander Mollinger, The Dolmen of Tynaarlo, 1861.
  • Hendrik Dirk Kruseman van Elten, Hunnebed, 1982.
  • Johan Driedé, Dolman at Eext, 1927,
  • Johan Driedé, Dolman at Eext, 1927,
  • Johan Dijkstra, Dolman at Loon, undated.
  • Vincent van Gogh, The Peat Barge, 1883.
  • Taco Mesdag, Landscape with Stacks of Peat and Three Women, undated.
  • Reinhart Dozy, The OranjeKanaal, circa 1933.
  • Reinhart Dozy, Village Celebration in Elp
  • André Idserda, Church in Dwingelo, circa 1920.
  • Geesje Mesdag-Van Calcar, View of the church de Vries, undated.
  • Julius van de Sande Bakhuyzen, Landscape near Rolde, circa 1895.
  • Anton van Rappard, Landscape near Rolde, 1882.
  • Arie van der Boon, Fram in Rolde, undated.
  • Louis Albert Roessingh, Windmill in Elp, undated.
  • László Paál, Landscape near Beilen, 1871.
  • Saskia Boelsums, Erica, 2019.
  • Siemen Dijkstra, Morgenland - Rondveen Dwingelo, 1998.
  • Berend Groen, Streamscape near Taarlo, 1998.
  • Berend Groen. Old cementry near Loon, 1983.
  • Reinder Homan, Tritypchi: Drenthe Aa River, 1995-1996.
  • George Hendrik Breitner, Peasant Ploughing in Drenthe, 1885.
  • Willem Hamel, Landscape with a Woman and a Goat, undated.
  • Jozef Israës, The Drenthe Madonna, 1893.
  • Max Liebermann, Preparatory Study for the Bleaching Ground in Zweerloo, 1882.
  • Max Liebermann, Child under Trees (preliminary study for children playing), 1882.
  • Julius van de Sande Bakhuyzen, Cow Herder Resting on the Bank of a Stream Bordered by Tree, undated.
  • Arnold Marc Gorter, Country Road in Drenthe, circa 1900.
  • Jan Meine Jansen, The Kamperzand Heath, 1934.
  • Hendrik Willem Mesdag, Landscape near Vries with Peasant Ploughing, 1877.
  • Alphonse Stengelin, Rising Moon, circa 1879.

From the exhibition Saskia Boelsums. I found the following works notable:

  • Landscape #07, 2016/2017.
  • Landscape #04, 2016/2017.
  • Landscape #22, 2016/2017.
  • Landscape #62, Bargerveen, 2018/2019.
  • Landscape #50, Drenthe, 2018/2019.
  • Landscape #11, Ameland, 2016/2017.
  • Landscape #26, IJsselmeer, 2016/2017.
  • Landscape flowers #07, Börkener Paradies, 2016/2017.
  • Landscape #35, Bergerveen, 2016/2017.

From the exhibition David Schnell - Saison, I found the followin works notable:

  • Stanze, 2018
  • Niemandsland, 2017.
  • Pascal, 2019.
  • Kanal, 2019.

While walking through the rest of the museum, I also saw two works bij Jan Sluijters: Baadsters in zee, 1995, and Damesportret. We also the exhibition Wout Muller. At 13:39, I bought a round Goki puzzle and four cards with works on display at the museum shop.

LOFAR superterp

In the afternoon, we visted the superterp of LOFAR. We only saw it from a distance. I parked the car at the end of the road Achterste Velddijk and walked along this road where we encountered the CS032 base station. We turned right on Beeksdijk. Along this road there are two square pillars with some information about LOFAR. We walked along base station CS001 and took the small path through the fields. When coming close to base station CS011, we saw large flocks of goose take-off, probably scared by our presence. We also found some mint plant, probably mentha aquatica. We crossed a bridge and walked till the next turn in the path, which is the closest you can get to the superterp. But there was not much to see due to lots of reed plants on this side of the superterp. Had we continued, we could have walked 'through' base station CS017, but we returned the same route we had come there. We collected some of the mint on the way back. Conny took many pictures. When seeing these pictures, I was a little suprised by the many contrasts between the pictures she took.

Tuesday, July 28, 2020


At 15:12, I bought the book De koningen van weleer written by Willem Gijsen in Dutch and published by Meulenhoff in 1981, ISBN:9789029010153, from charity shop Het Goed for € 0.75.

Sunday, July 26, 2020

Wigbold route

Conny and I, followed a walking route (description in Dutch) along historic places in Enschede following the six wigbold markers, that marked the area outside of the city of Enschede to which the city laws applied. Originally, these were marked with field boulders. It is not known on which dates these boulders were placed, most likely after Enschede received city rights around 1300, which were confirmed in 1325 by Bishop Jan III van Diest and henceforth allowed Enschede to protect itself with a wall. In 1818, it was decided that the six stones would mark the border between the city of Enschede and the county of Lonneker that surrounded it. In 1826 the boulders were replaced with Bentheimer stone posts. In 1934, Enschede and Lonneker were joined and the border poles lost their function. The six stones that are now placed near the original locations (but one is on the original location) are replicas.

In the route also two old graveyards were included. Both graveyards were outside of the city borders when opened, but are now well inside the city borders. Both have been closed for almost a century, Both contain graves of from important families of the textile industry that dominated Enschede. Both graveyards fell into disrepair and some effort has been put into restoring them. At the entrance of the the 'boeren' (Dutch for farmers) graveyard, there is a sign signaling that alcohol and drug use is forbidden and that group formation prohibited, but is seems that both are still taking place. In that graveyard we also found a rather modern looking memorial stone for Tommy Tattersall, who at the age of 17 died in 1887 after being kicked in his stomach during a soccer game. Thomas "Tommy" Tattersall and his brother Stephen came to the Netherlands with their parents in 1876. The family was included in the Enschede upperclass, where they explained British soccer to their Dutch peers. His father owned a factory supplying machines to the textile industry. Saturday, three weeks ago, the memorial stone was revealed again after it was being clean-up and recovered from some location outside of the graveyard. The memorial has the form of a broken tree. We found some other examples of this symbol on the other graveyard. We also found several graves with an ouroboros and two crossed, upside-down torches on it.

Tuesday, July 21, 2020

From 543 to 987

Today, it was reported that the number of COVID-19 infections in the Netherlands almost doubled from 543 to 987. On a radio show, Ab Osterhaus pleaded for more testing and contact research. He says that we, the Dutch government, do not have a consistent policy to eliminate the virus. He feels the discussion is too much about the hospital capacity and that we accept that the virus remains in the country. He argues that it is very difficult to change the behaviour of people and that the government should focus on testing and contact research to avoid the situation where another lock-down has to be enforced, which will have serious repercussions on the economy.

CampZone 2020 "Ærpane" badge

I received CampZone 2020 "Ærpane" badge. Assembling was rather easy with the instructions. (I think, it would be better to first plug in the small loudspreakers and then put them in such that the wires are straight. I felt it was easier to first plug in the flat cable before connecting the two printed circuit boards.) It took me a long time to access the badge through the website. I installed the Brave web browser and added a rule for the USB drive. It only worked after a reboot.


Friday, July 17, 2020


There are some flowers in our magnolia but only a few have fully opened. The little chestnut tree, that looked like it had died, has started to grow some leaves. I try to water it regularly.

Wednesday, July 15, 2020


At 17:30, I bought the book aki eindexamen fotografie 1999 written by Rutger ten Broeke. edited by Marcel Vos and Tjipke Meijer, written in Dutch, and published by AKI in 1999 from charity shop Het Goed for € 1.50.

Monday, July 13, 2020

Comet Neowise

Just after midnight, Conny and I left on our bikes to the road called Helweg to see if we could see comet Neowise. When on the Helroad we saw the comet. We stopped at a crossing of the road and used a tripod to take some pictures from the comet and also from the rest of the sky. I took a picture of Jupiter with four dots around it, the moons Europe, Io, Ganymede and Callisto. I used the excellent website StellariumWeb for locating the comet and finding the information about the moons around Jupiter.

Sunday, July 12, 2020

Data Synth

This afternoon, I went to the first Geluidsdrug event in Twente at Spacebar in the city center. I attended the workshop help by Error Instruments and build a Data Synth noise generator. I also played a little in jamsession with the Noise! synthesizer (which I build on May 29, 2016), the Greep Cluster (which I build on September 8, 2017), and Noise Engine 1 (which I designed and build on May 26 this year).


I have been trying to reproduce the workings of the HEK program, which Peter Struycken used in 1976 for designing a fence around the tax office in Zwolle. I started looking into this, when I was informed about an attempt by someone else. The catalogue Beelden en Projecten gives a description of the algorithm along with some drawings and graphs. The algorithm given some input parameters and a random series, generates a series of angles and lengths. These angles and lengths are used to generate a line drawing based on line segments. I wanted to determine the multiplication factor that was used for the series of lengths and I thought I could do this by reverse engineering the random series from the series of angles (which could be derived from a design drawing). This did not work as easy as expected. I came to the conclusion that the series of angles are not used as absolute angles but as relative to the previous line segment. A conclusion that seems to match with the description of the text. But then it still did not work using the parameters in the text. To avoid errors in the angles and lengths I had manually measured, I took a picture of one of the design drawings and tried to measure the coordinates of the line segments more accurately. Because that did not resolve all the issues, I decided to first verify the algorithm with the graph showing the various input and output parameters of the algorithm. Tonight, I concluded that the graph has an error with respect to the line representing the random values. One of the points is at 0.72 but it seems that according to the algorithm it should have been close to 0.07, which looks like a simple displacement of period error, presuming that the graph was hand drawn.

Wednesday, July 8, 2020

Testing for COVID-19

Six foreign students of the University of Twente, who wanted to travel abroad and were required to be tested, tested positive to COVID-19 to their surprise because they did not have any of the symptoms. They are all living in the Hogekamp building that has about 450 rooms for student of which about 80% are foreign students. Some foreign students from China were surprised that not everyone in the building was required to be tested. Although there is sufficient testing capacity, only people with symptoms are advised to be tested. The official statement is still that it has no use to be tested if you do not have any of the symptoms. The public health organizations are doing contact follow-up on everyone who tested positive, but it seems that those people are only advised to have themselves being tested if they have or develop symptoms. I am a little worried that if six random people test positive without showing any symptoms (and not knowing anyone who tested positive) what that means to the number of (young) people who are now infected without having any symptoms. It is possible that now a larger percentage of people are infected without showing any signs of the infection due to seasonal effects (such as higher vitamin D levels). I presume that testing is not expensive compared to the possible economical costs in case another lock-down is required when in the fall the number of people who develop serious symptoms is on the rise again. Yet our government still seems not to attempting to reduce the number of infections as much as possible, but to keep it below a manageable level.


Saturday, July 4, 2020

TSP solver

In the past week, I tried to find out if there was an even shorter route to complete the AKI MUPI route. I first tried the TSP Solver and Generator. Took me some time to generate a binary .tspt file in the right format. The solver very quickly found a solution of more than 28Km, not even close to the shortest route I had already found. Next, I wrote a recursive back-tracking solver. It worked, but did not make much progress, until I made some modifications that strongly reduced the number of alternatives searched on every level. It did find a shorted route, starting from home and visiting: C, E, I, Q, J, F, G, H, L, K, M, N, O, P, g, a, Z, Y, W, X, l, k, j, i, h, f, e, d, c, b, V, U, T, S, R, B, A, D, and back home where te letters refer to the points on the map, I presented on June 27. Next, I implemented a batch solver, which starts with a batch of 'smallest' possible solutions and extends these in steps. With a batch size set to 5000, this algorithm did not find any shorter algorithms. I added some of the output to the source of the program.

Sunday, June 28, 2020

AKI Mupi route

Today, I biked the route (in Google Maps) I found yesterday, although I followed the route by heart (except for some small change), I missed one of the Mupi's along the route. It was the Mupi with a reproduction of the works by Julia Hofman. I left at 9:29 and returned at 12;03. Below the list of Mupi's I encountered with a short description of the work as I precieved it.

Saturday, June 27, 2020

Planning AKI Mupi route

I wanted to find a route to visit all the Mupi's of AKI Finals Mupi route. I spend some hours drawing connection routes (with Google Earth) between the mupi locations and noting down the distances. (The results in KML file or Google Maps.) I made a drawing of this:

Finding a shortest route is the Traveling Salesman Problem as a graph. I searched for a solver. I came across TSLIB95. I installed TSPLIB 95, but when I enter the import tsplib95 in Python 2.7.17, I get a SyntaxError on line 5 of bisep.py. The pages do not mention which version of Python should be used. I downloaded tsp_brute from Brute Force Solution of Traveling Salesman Problem and got it compiling with g++ with some modifications. Next I wrote a program to generate the matrix from the graph. The tsp_brute took a long time crunching and I killed it after some time without it producing a solution or showing any sign of process. I tried to find some route myself, and fount a route of length 26.181 meter. Next, I wrote added an algoritm that incrementally removes the longest connection lest any node get less than two connection. From the resulting list of fragments, soms cicular, some with branches, I constructed another route with a length of 25.641 meter.

Thursday, June 25, 2020


Tuesday, June 23. 2020


Monday, June 22. 2020


Sunday, June 21, 2020

Father day present

Annabel gave me a pyramid maze, which she has made from wood with a laser cutter and for which I wrote the program. Below a photograph of the maze.

Friday, June 19. 2020


Wednesday, June 17, 2020

Suguru puzzles

I wrote a program to map Suguru/Tectonic puzzles on an Exact Cover. The exact cover solver should be able to read the input of a number of columns separated with commas, where the numbers may be in any order. The program reads the input from the standard input. An example of the input format is:

| |4  |4  |
*-* * * * *
| |  1|  2|
* *-* * *-*
|   | | | |

Monday, June 15, 2020

Red rainbow

When at 21:56 I left home the sky was red due to the sunset. It was also raining a little and I saw a faint single but complete rainbow. I also noticed that it was quite red. Just before ten, I took a picture, which is show here, after I increased the saturation a little to increase the visibility of the the rainbow.

Wednesday, June 6, 2020


Monday, June 6, 2020


Saturday, June 6, 2020


Thursday, June 4, 2020


At 17:17, I bought the following books from charity shop Het Goed:
  • De Eersten van Rissan written by Wim Gijsen in Dutch and published by Meulenhoff in 1984, ISBN:9029011432, for € 1.65.
  • Bovengronds: 15 jaar kunstbezit bij Gasunie edited by Chris de Boer and Jan Hekman, written in Dutch, and published by N.V. Nederlandse Gasunie in November 1997, ISBN:9789071728150, for € 1.45.
  • One hundred thirty seven thousand and sixty-one edited by Dorrie Tattersall and Petra van der Jeught, written in English and published by Jan van Eyck Academie in 2009, ISBN:9789072076885, for € 3.00.

Monday, June 1, 2020

Sunniest spring

The past three months, where the most sunniest on record. On average over the whole country we had 790 hours of sunshine while on average there are 517 hours. The previous record from 2011 was 743 hours. It was also very dry. We only had (on average over the whole country) 77mm where 172mm is normal. The weather station at Twenthe Airport measured 752.2 hours of sunshine and 95.5mm of rainfall.

Sunday, May 31, 2020


Conny and I went on another hunt for border poles. This time our goal was the Drilandstein, a border pole on the border of The Netherlands and the German states North Rhine-Westphalia and Lower Saxony.

The poles we encountered are:

Some links (in Dutch) with information about poles along the route that we took:

Tuesday, May 26, 2020

Noise Engine 1

In the evening, I went to TkkrLab, where there were but a few people. I bought a breadboard from the vending machine and went to experiment with the 40106 IC from the 4000-series integrated circuits, which has six inverting Schmitt triggers. I used three of these to make a circuit. For a short demo, see the Noise Engine 1 YouTube video.

Monday, May 25, 2020


August 2020
July 2020
June 2020
May 2020
April 2020
March 2020
Alzheimer's Disease
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