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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.

Saturday, November 9, 2019

Berlin Geisterbahn

Today, it is 30 years since the fall of the Berlin Wall. I went to visit Rijksmuseum Twenthe to see the exhibition Berlin Geisterbahn with pictures by Fons Brasser, which he took from ghost stations from the Berlin S-Bahn, the rapid transit railway system of Berlin. I studied the four maps, from different periods, of the S-Bahn that were on display, and tried to relate them. I took one of the information sheets, with a picture of the Schulzendorf station on the back, that had a map of all the S-Bahn stations during the period the pictures where taken in the first half of the eighties. All the ghost stations are marked with colours on this map.

Tuesday, November 5, 2019

Wifi trackin

The city of Enschede is using the services of the Dutch company City Traffic to measure footfall in city center. The company cleams that this is privacy proof. According to the Dutch GDPR laws, it is forbidden to track people using MAC addresses of their mobile phones. City Traffic defends themselves by stating that they are not storing MAC addresses but are anonymizing the addresses by applying a some hash function. They also have an opt-out register on their website. I wonder if they actually apply the same hash function to the MAC address entered there in the browser or that the MAC address is only hashed in their server. I would like to be opted-out, but not that they process my MAC adres any any form without my explicit permission. On the opt-out page, there is no mentioning of giving them the right to process the MAC address, which I think they should according to the Dutch GDPR laws. The fact that they do have an opt-out mechanism, seems to imply that they are not truely anonymizing the MAC addresses, but that they could still track my MAC address if someone would give it to them.

Sunday, November 3, 2019

Average distance

A property of a maze is the average distance between all the rooms, where the distances is defined as the number of passages on has to pass to arrive from one room to another room. To calculate it, you first have to calculate the (shortest) distance between all combinations of rooms, and than sum all those distances. To calculate all the distances, one could use the Floyd-Warshall algorithm, which requires a matrix of the size of the number of rooms. Because the distance is direction independent, the matrix is symmetric, and one only needs to store one half of the matrix. Still the memory consumption grows quadratic with the number of rooms. However, to calculate the average, one only needs to how often a certain distance occurs. As an alternative one could sequentially calculate the distances from each of the rooms using Dijkstra's algorithm. This would only require a memory storage linear equal to the number of rooms. If the maze is 'nice' in the sense that there is exactly one route between every two pair of rooms, one could use any recursive algorithm to visit the rooms starting from the first room. Once the distances are calculated from one room, one can count how often each distance occurs. These counts can easily be summed (using a storage equal to the number of rooms) for all the rooms. Note that each distance is counted twice, but for calculating the average distance this does not matter. This algorithm requires one to traverse the maze as many times as there are rooms. Last night, I came up with an algorithm for nice mazes that only require you to traverse the maze once, and which does not count the distances twice. While walking through the maze it keeps a list of distances from the rooms visited. When arriving in a new room, this list is used to update the global list of distances. If the room has only one passage not visited yet, the list is simply extended with room. This is done by adding the room to the front of the list and letting the position of in the list determine the distance. If there one more than one exit left that has not been visited, the current list is assigned to the room and an empty list is passed for the next step. After returning from that part of the tree, the list from there and the list kept at the room, can be used to calculate all the distances between the rooms counted by both list, and after this has been done, the two list can be added together for the remainder of the tree. (If there is still more than one passage not visited, the added list is again assigned to the room, otherwise it is passed to the next step.) This afternoon, I implemented the algorithm in the function _calcDistances in MazeGen.cpp, the maze generation program I have been developing.


Saturday, October 26, 2019

In to the city

While biking to the city, I stopped at Kringloop Enschede. At 15:57, I bought the following two books:
  • De tweede helft: beeldende kunst na 1945 written by Ad de Visser in Dutch, published by SUN in 1998, ISBN:9789063037833, for € 3.00.
  • Pier+ocean: construction in the art of the seventies : an exhibition written by Gerhard von Graevenitz and Norman Dilworth in English and published by Arts Council of Great Britain in 1980, ISBN:9780728702394, for € 1.00.
I went to Concordia to watch the short movie: Fake Fiction, which is part of the exhibition Untitled Surface by Filip Markiewicz. On Sunday, September 29, I already saw this exhibition and watched part of the movie. Now I took time to see it from the start to the end only to discover that I already saw almost the whole movie. Nevertheless, it was an interesting experiecnce. After having eaten an ice cream (temperature reached 19.9°C at the weather station at Twenthe Airport), I went to bookshop Broekhuis, where at 17:12:58, I bought the book Famous For 15 Minutes: My Years With Andy Warhol written by Ultra Violet in English and published by Methuen London in 1989, ISBN:0413615308, for € 12.50.

Friday, October 25, 2019

Books and exhibition

At 16:27, I bought the book On the Road written by Jack Kerouac in English and published by Penguin Books in 1998, ISBN:9780140274158, from charity shop Het Goed for € 1.30. In the evening, I visited the last day of the exhibition Mixed (up) at B93. Around 18:25, I bought the artist book Street Poetry I. (5/30) from Esmee van Zeeventer for € 15.00 and also the artist book Crisis Sale (57/100) from Patric Jonkman.

Wednesday, October 23, 2019

Rule 30

When I read about Rule 110 being Turing complete, I adapted a program that I wrote for Rule 30 such that it works for Rule 110. The results looked promissing. Yesterday evening, I spend some time to write some JavaScript code to display the results. When today, I applied this to the results for Rule 110, the results where somewhat disappointing. A lot of repetitive patterns and some of the expected patterns did not appear. Below the visualisation of repeating patterns up to the area of 100. (A manually removed some dupplicates, so the list might be incomplete.)

This text is displayed if your browser does not support HTML5 Canvas.

Today, I read that Stephen Wolfram announced The Wolfram Rule 30 prizes, which are about the randomness of Rule 30. I think that all three questions are true, but very very hard to prove.

Monday, October 21, 2019


Tuesday, October 15, 2019


Sunday, October 13, 2019


In the afternoon, I visited XPO to have a look at the exhibition Unravel with work Rhizoma by Melle Foortjes and the work 111 days in Jerusalem by Judith Glimmerveen. The exhibition is part of the Fotomanifestation Enschede. They are two students from AKI.

Crossless mazes

I was thinking about generating mazes in a rectangle of squares that have the property that non of squares with four squares to the left, the right, the top and the bottom, has no walls, e.g., is like a cross. One way to generate these is thus to allow such cross squares and apply an algoritm to elimintate them one by one. We assume only nice mazes, which are mazes where every two squares can be accessed through exactly one route, or in other words where the passages form a tree graph according to graph theory. I think the following algorithm works. As long as there is a still cross square, pick a cross square that is furthers away from the top left corner, where distances is calculated by adding the distance in horizontal and vertical direction. Now change either the passages to the top or the left into a wall, which makes that the square is no longer a 'cross' square. With doing this, some squares will no longer be reachable from the top left square. Now, either the square to the left or to the top will be included into these squares. Note that this square is closer to the top left square. Possibly there is even another square even closer that now no longer can be reached from the top left corner. Pick one of these squares. Now it must be that this square has only passages to the right and the bottom and that if there is a square to the left or the top, it must be reachable from the top left corner. Turn the wall into a passage for either the top or the left square. This might turn the square into a cross square, but that cross square is closer to the top left corner. Each step, will either remove a cross square or replace it by a cross square closer to the top left corner. (An implementation of the algorith could make some smart choices to prevent the latter case.) Because there is only a limited set of squares that might have to changed into a cross square, and this set becomes smaller whenever the last cross square at a certain distance is eliminated, the algorith must come to a halt, resulting in a maze that does not have cross squares.

Saturday, October 12, 2019

Museumnacht Enschede

Annabel and I went to the Museum Night Enschede. We had dinner at a local food hall. First we went to Concordia. We looked around a bit. The music from DJ Southern Depot was a little overshadowing everything. Did look a little at VJ The C-men. Next we went to Sickhouse. Here we saw (the last half) of Patric Jonkman performing with his (relatively small) modular synth to silent movie The Cabinet of Dr. Caligari and Thom Floris performing to chapter 1 of the silent movie Häxan. From this we went to Rijksmuseum Twente. I showed Annabel the painting by Claude Monet. I sat on the ground while listening to the performance of Lotte Pen and immediately slipped into a meditative state. She performed: Triptych, Chronon, Patternalism, and Tabernacle (if I remember correctly). We looked around a little more and paid short visits to the AKI and Tetem art place before going to De Museum Fabriek. There we joined the last demo of the oldest Zeiss Mark I planetarium projector, which is in the process of being restored. It was damaged during a fire in 1976 and had been in a storage room for a long time. It was only last year that the restoration started. It is not finished yet. Many of the projectors are not aligned correctly yet and need to be adjusted. (In 1968, I saw this planetarium in The Hague together with my father, my brother and two of my sisters.) We drank some tea in the cafe of the museum before we went home at midnight.

Thursday, October 10, 2018

Moleskin daily planner

At 17:26:43, I bought a Moleskin daily planner for 2020 from Bookshop Broekhuis for € 21.99.

Monday, October 7, 2019

Checking maze

I am working on a program for generating mazes and I wanted to implement an algorith to check if a maze is 'nice', meaning that from every 'room' you can reach any other 'room' and that there is exactly one route between any two rooms, or in other words, that you cannot walk in a circle. (In graph theory the nice maze is similar to a tree graph.) I was thinking about all kinds of rather complicated algorithms to check these properties, until I realized that there was a very simple algorithm. This algorithm depends on the property that you can walk through a maze by following the wall on your right (or left) side. With a closed maze, you will return to where you started. If the maze is nice, you will visit every passages (between two rooms) in both directions. The number of passages for a nice mazes is one less than the number of rooms and thus easy to calculate. If the maze is not nice the number of passages you pass while following the wall will be lower than twice the number of passages. If some rooms are not reachable from each other, you will not visite them during the walk, and thus the number of passages you count will be lower. If all the rooms are connected, but you can walk in a circle, than you will never be able to walk around and touch all the walls, meaning that you will only follow some passages in one direction and not two directions. Thus the number of passages you pass will also be lower.


Wednesday, October 2, 2019

Mixed (up)

In the evening, I went to the opening of the exhibition Mixed (up) at B93 with photographs by Esmee van Zeeventer and Patric Jonkman. I talked a bit with Esmee and told her that I am interested in buying a copy of the (small) book she wants to make with some of her photographs. I also talked with one of her former teachers about photography and art.

Sunday, September 29, 2019

Fotomanifestation Enschede

I joined the opening walk of Fotomanifestation Enschede. The theme of this photo manifestation is Inner Circle. The first exhibition is Sistaaz of the Castle by Jan Hoek at Fotogalerie Objektief. It is about seven transsexuals in Cape Town. In the galery there were also small mobile gardens in old soccer balls or baskets. The organization to support them is Support Sistaazhood. Next we went to Concordia for the exhibition What Goes Up by Sylvie Zijlman. Upstairs, I also had a look at the exhbition Untitled Surface by Filip Markiewicz and watched part of the movie Fake Fiction. At bookshop Broekhuis, the exhibition Geachte Afwezige... with photographs by Paul Hajenis was opened. At Rijksmuseum Twenthe, there were two exhibitions part of the walk: Where Will We Go by Kadir van Lohuizen and Setting The Stage by Eddo Hartmann. From this last exhibition, I did like the picture Housewife Somun Street, Pyongyang, 2015 the most. While at the museum, I walked through the exhibition Tischbein en de ontdekking van het gevoel but did not pay much attention. I did get interested by the associated exhibition by Melanie Bonajo, the photo collage Thank you for hurting me. I really needed that... and some video. I also had a second look at the exhibition of works by Peter Zegveld and verified that some of the horns in one of his installations were in the incorrect order. Of course, I also took some time to look at Falaises près de Pourville by Claude Monet and Gezicht op Louveciennes in de herfst by Alfred Sisley. The last opening, was at Het Arendsmanhuis. It was the opening of the exhibitions Charlotte and Emily Salvia by Linsey Kuijpers.

Saturday, September 28, 2019

FPGA course

I joined the FPGA course at TkkrLab organized as part of the bimonthly CyperSaturdays. The course was developed and given by Paul Honig from RevSpace and is based on the UPDuino v2.0 sold by Gnarly Gey. The course started with the elementary priciples. During the course, we mostly focussed on programming the (very bright) RGB-led on the board, but sources for reading the digital temperature sensor (DS18B20) are included.

Allée Rentrée

In the evening, I went to Allée Rentrée festival with art and music. He liked the following:
  • FE 26 by David Scheidler
  • Electric Guitar Paintball Sniper by Ole Nieling
  • Devotie by Erik Kok
  • Paintings by Bas van der Linde.

Tuesday, September 24, 2019

Flap Flap

I went to see the Flap Flap installation by Philip Vermeulen at the University of Twente. I was a little late for one of the performance, so, I only watched the last third of it. I did not have time to wait for the next performance.

Monday, September 23, 2019

Walking at Night in NYC

I watched the Walking in Heavy Thunderstorm at Night in NYC video and tried to figure out the route the maker took. I discovered that there are six segments in the video (and a very short one, that I do not count). With Google Earth I made a KML file of the routes of each segment. It seems if the maker made two walks starting from East 34th Street and Park Ave, and that he alternated the segments from these walks, one in order and the other out of order.

Sunday, September 22, 2019


It felt like spring today. At the end of the afternoon, it was much warmer outside then inside. Temperatures reachted 26.6°C at weather station at Twente Airport. The garden looks very green again compared to a few months ago. It seems that the leaves of the small chestnut tree have withered. I hope it has not died. I tried to water it through the summer when it was dry, but I might have forgotten it.

Friday, September 20, 2019

Dead end?

With the results of last Sunday, I tried to find the 35 constant weight vectors for A(11,4,4) as mentioned in a table. I did this by starting with the 54718 solutions consisting of 19 vectors and try to extend it further. The program found 46080 solutions (possibly containing doubles and missing some) consisting of 30 vectors and non with more than 30 vectors. It looks like a dead-end. Which actually does not surprise me, because requiring that 18 vectors will be close to one vector, might force them to be spread apart too far and in a some what regular manner, that no space is left over to select the remaining sixteen vectors from.

Thursday, September 19, 2019


Tuesday, September 17, 2019


Sunday, September 15, 2019

54718 solutions

I continued working on the program to calculate the number of different solutions of 18 constant weigh vectors 'around' a vector with seven ones and four zeros, where around means at a Haming distances of four and such that all vectors are at distance of at least four. The program found 54718 different solutions taking in consideration all possible permutations of the 'rows' of the vectors.

Saturday, September 14, 2019


I went to Tetem art space to look at the exhibition Xenobodies in Mutation. At the Exploring-Lab some people were assembling a small motor powered by solar cells. I also joined and assembled one.

Wednesday, September 11, 2019


I recieved the book Kilo-Girls written by Julia Luteijn in English, which I bought from the author for € 13.90 (including postages).

Tuesday, September 10, 2019


November 2019
October 2019
September 2019
August 2019
July 2019
June 2019
Alzheimer's Disease
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