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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.

Thursday, November 26, 2020


Tuesday, November 24, 2020


  • MyNOR is a single board computer that does not have a CPU.

Monday, November 23, 2020

Topographic atlas

At 17:30, I bought the book Topografische atlas van Drenthe written by Thomas Termeulen in Dutch and published by De Vrije Uitgevers in 2015, ISBN:9789077350805, from charity shop Het Goed for € 2.50. Although it is called an atlas, it is actually the loose-leaf edition, consisting of 104 maps (printed double sided), with references to each other.

Saturday, November 21, 2020

Four marke linden tree

Conny and I went searching for some marke stones. First, we visited the border between the townships Haaksbergen and Enschede on the main road connecting the two cities. There we located the Goorpaal, a replica, which was placed on September 19, 2020 on a slightly different location from the original stone that was placed around 1825 at the border of the marke Haaksbergen en Honesch and the marke Usselo. Next we went to the water treatment area called Kristalbad, which is located between Enschede and Hengelo and is filled with effluent from the wastewater treatement plant of Enschede. The border of the marke Twekkelo and the marke Groot Driene crosses through the Kristalbad. The border can easily be recogned from aerial pictures. On one of the (inaccessible) islands there is an original marke stone, known as Koekoeksteen. After having walked around the area, we went to University of Twente where we looked at the marke stone known as 'Steen tussen het Driener en Twekkelerveld'. We drove a little further and parked the car on a road called 'De Achterhorst' near some houses of employees of the university. We walked along a path at the border where we found another marke stone called 'Steen aan het hooiland van Van Heek' to arrive at the tree (a lime tree) at the cross point of the four marke Groot Driene, Twekkelo, Esmarke and Lonneker, called Viermarkenlinde, which translate as four marke linden tree. Not far from this tree, there is another marke stone, called 'Paal op het erf van Helmich van Heek', but it is on private property and thus not accessible. We walked around the area, including the Abraham Ledeboer park (which has a one of the highest sequoiadendron giganteum trees in the Netherlands) and ended up encircling the marke stone. highest

Thursday, November 19, 2020


Tuesday, November 10, 2020


Sunday, November 8, 2020


Today, Conny and I went searching for the marke stone known as Broekheurnerpaal, which is on the border of the former marke Buurse and Usselo, which now is the border of the townships Haaksbergen and Enschede. We discovered that it could be reached by walking along a channeled brook. We found it around 12:09. We continued walking along the brook, but decided to return about half way to the next road. We saw three deer walking in the fields. They came towards us, but changed course when they became aware of us. They jumped over the brook a few hunderd meter from us and dissapeared in the fields. A little further we noticed that the field was covered with cobwebs that was slowly dancing in the little wind there was.

Saturday, November 7, 2020

Walking in Twekkelo

Conny and I went walking in Twekkelo around the road Zwartevenneweg and the road Grote Esweg. We both had not walked around and were a little surpriced by the number of cars on the parking lot near the entrance of the area. We had come by bike. In the area also the marke stone called 'Steen op Christinalust' can be found, which marks the border between the marke Usselo and Twekkelo. When walking around the area, we found many different types of mushrooms and fungi, some of which we had not seen before.

Monday, November 2, 2020

Palindrome date (DD-MM-YY and YY.MM.DD)

Today is a palindrome date when written according to the DD-MM-YY format: 02-11-20 and the YY.MM.DD formats: 20-11-02. The previous such date was November 21, 2012 and the next will be November 12, 2021. This is the sixth special date of this year.

19.4° Celcius

Last night the temperature did not drop below 16.7°C (at the weather station of Airport Twente) and around seven in the morning, the old record of 18.1°C of highest temperature on this day in 1968 was already broken. In the early afternoon, the record temperature of 19.4°C was reached.

Sunday, November 1, 2020

Marke stone and border poles

Conny gave me the book Landscape Photography with text and photographs by Saskia Boelsums and published by Terra Uitgeverij in 2019, ISBN:9789089898104, for my birthday. We saw some of her photographs at the Drents Museum on July 29.

In the morning, when the weather was still a bit sunny, and we took the car to search for some marke stones and border poles. We first went to search for the Fabbelhuttensteen marke stone, which we could not find on August 3. Now that the corn has been harvest, it was easy to find. Next we searched for the border pole near the Grenzweg in Gronau. We walked past it on May 31. At 11:20 we found the border pole 845-Y. We saw pole 845-X again. We drove to Arendsweg. There we walked along the border towards the south. We walked along pole 804-G, which we found on May 21 and found 804-F. We hoped to find another pole, but we did not. We also followed some other path between fields with cows in the direction of the border, but it ended before reaching the border.

Sunday, October 25, 2020

PARR books

I have been working on a program to generate books with PARR patterns. Nowadays, there are many sites that can print books on demand with all kinds of options with respect to quality of the paper and means of binding. All you need to provide is some PDF files. I spend some time figuring out if I could use (La)TeX to generate a PDF. It proved not so easy, as I wanted to have one PARR pattern on each page, exactly aligned. So, I decided to use PostScript and convert it to PDF. (There are tools for combining PDF files.) The program tries to generate an interesting set of PARR patterns (for a given number of lines and points). It does this by avoiding patterns that are symmetric and combinations of patterns that are very similar. It also tries to find a printing order in which similar patterns do not appear close to each other. Everytime when the program is ran, it generates a new set of PARR patterns.

Saturday, October 24, 2020

Visting city center

It is the first time in at least a month that I visited the city center. At Fotogalerie Objektief I saw the exhibition Beautiful world with photographs by Donny Scholten-Coelet and at Concoria I saw the exhibition Wayne Horse - May all your dreams come true. At 15:38:21, I bought the book Veldnamen in Enschede written in Dutch and published by Uitgeverij Van de Berg in 1992, ISBN:9070986888, from bookshop Broekhuis for € 19.95. Alongside the book also a set of maps.

Thursday, October 22, 2020

Henk Helmantel

Conny and I went to Drents Museum to see the exhibition Henk Helmantel - Master Painter. We had tickets for a time-slot in the afternoon. So, we first went to visit the Westerbork Synthesis Radio Telescope. We started at the parking place of the National Westerbork Memorial and followed the path with models of the planets (including the minor planet Pluto) and the sun on scale of their (average) relative distances. This path ends at one of the end of the row of radio telescope.

At the Henk Helmantel - Master Painter exhibition, I noted down the following works in the order I saw them:

  • Self-portrait in his studio, 2013
  • Self-portrait, 1980
  • Snowdrift on the dwelling mound of Westeremden, 1980
  • View from the studio window, 1985
  • Vegetable still life, 1985
  • Still life with large roemer and quinces, 2011
  • Still life with quinces and two bottles, 2019
  • Still life, 1988
  • Bronze bowl with three eggs, 2000
  • Ode to the Father, the Son and the Holy Spirit, 2019
  • The Cloister of Le Thoronet, 2001
  • The choir of the church in Bozum, 2003
  • The chapter house of the abbey of Le Thoronet, 2002
  • Still life with a white bowl, 1991
  • Still life with Roman glass and a Chines skirt on a Spanisch table, 2001
  • Still-life composition with a homage to Kees Stoop, 2006
  • Still life, 2000
  • View of the South wall of the church of Oldenzijl, 2019
  • The choir of the church of Oldenzijl, 2011
  • Open window in the medieval stein haus in Bunderhee, Germany
  • Two oranges, 2018
  • Oranges and tangerines, 2018
  • Fifteen intimate still lifes
  • Onion still life, 2015
  • Chestnuts on a red floor, 1998
  • European archealogical glasse, 2003
  • Chinese jar on top of a red cabinet, 2002
  • Chinese cabinet with a open door, 2015
  • Still life with Roman glass, 2004
  • Chinese bronze objects, 1997
  • The apostle James of a Gethsemane group, 2005
  • Still life with tree pots from Europa, South America and Asia, 1992
  • Mexican pot, 1994
  • Still life with Drenthe archeaological finds, 2004
  • Still life with a chinese Han vase and a bronze bowl with oranges, 2020
  • Rembrandt chalk-glue pot (Phase 1, 2 and 3), 2000
  • Window in the choir of the monastry church in Le Thoronet, 2019
  • The Pieterskerk in Utrecht, 2014
  • The east side of the gatehouse of Ammersoyen castle, 2019
  • The hedgehog, 1988
  • Chinese eggshell bowl, 1977
  • Asparagus, 1988
  • Belgian endive in a yellow box, 1992
  • Still life with grapes, 2005
  • Still life with pome granates, 2002
  • Japanese doll, 1889
  • Box from Taiwan, 1998
  • Still life with worn family bible, 2004
  • Still-life composition, 2003
  • The most Dutch still life, 2019
  • Bread baked in emden, 2007
  • Book still life, 2020
  • Still life with monastery bricks, 2005
  • Large bronze water vessel, C.600 B.C., Shanghai museum, 2008
  • In the kitchen of de Weem in Westeremden, 2020
  • The cloister of sénanque, France, 2018
  • Inauguration of Queen Beatrix April 30, 1980 in the Nieuwe Kerk, 1981
  • The church in Leermens with thirteenth-century rood screen, 2011
  • The north aisle of the church in Leermens, 2000
  • The south aisle of the Romanesque monastery church in Jerichow, Germany, 2015
  • Ambry of the church in Heideby on Gotland, 2015
  • The choir of the church in Fide on Gotland, 2015

We also walked through the rest of the museum. We saw some drawings by Charley Toorop, all undated: Vrouw met kind, Drie mensen rond een tafel, Vier mensen rond een tafel, Boer, and Vrouwfiguur. We walked through the work Diasporalia by Koen Theys.

On the way home we went to the village De Kiel to visit the point where seven marken are joined. In 2004 a new stone was placed at the location where the original marke stone used to be. During the French period, there were no farmers who wanted to claim the area, which was surrounded by seven marken, namely: Westdorp, Ees, Odoorn, Sleen, Zweelo, Westerbork and Rolde. A land surveyor from the Land Registry under the command of Napoleon divided the land among the seven surrounding marken. The seven border lines are still visible in the landscape. The road is on a crossing of six roads, which are on six of these border lines.

Sunday, October 18, 2020

Walking and some border poles

Conny and I went walking around the Groot Bruning estate. Yesterday, it was sunny, but today the day started with fog, which changed into a grey sky. We found may mushrooms of all kinds in the forrest. The cows were still in the fields. Conny took a picture of the grey sky above the fields. Next we biked to the border, to check if we missed some border poles in some area. We found the following border poles: The first two we had seen before, but the last was a new find.

Thursday, October 15, 2020


Monday, October 12, 2020


At 09:51, I bought the book De Arnhemse School: 25 jaar Monumental Kunst Praktijk edited by Jonneke Fritz-Jobse and Ineke Middag, written in Dutch, and published by Hogeschool voor de kunsten Arnhem in 1994, ISBN:9074485081, from charity shop Het Goed for € 2.95.

Saturday, October 10, 2020


Last Thursday, I came along the article Computer Scientists Break Traveling Salesperson Record, which is about the report A (Slightly) Improved Approximation Algorithm for Metric TSP, which gives a slightly improvement of the Christofides algorithm. In the discussion on Hacker News, I found a reference to TSP-SA : Traveling Salesman Problem Solver using Simulated Annealing Algorithm. I spend some time, using this for the program I wrote to find the best AKI Mupi route. The solutions it finds are close to the shorters solution I found, but not very close. In the discussion on Hacker News there was some confusion about the presented result in the paper as it seems there are enough algorithms know that find much better approximations than the one reported in the paper, missing the point that the paper is about a theoretical result. Finding a near optimal solution with a program is one things, but proving that a given algorithm is always within a certain bound of the optimal solutions, is something completely different.

Tuesday, October 6, 2020

NASCOM microcomputers

I discovered that on July 13, 1979, I visited the offices of NASCOM microcomputers that developed and sold the Nascom 1 and 2 single-board computer kits. I had a random memory about bringing some eggs to an address while staying in Watford. I found some note of this in my diary V (written in Dutch) on page 72, where it mentions the name and the address of the company. (The address is mentioned in an ad in Personal Computer World of October 1979.)

Sunday, October 4, 2020


Saturday, October 3, 2020

Cause of the second wave

When I saw the graphs about the clusters of COVID-19 infections in the past months in COVID-19, Tweede Kamer briefing, Update Tweede Golf - II, 29 sept 2020, the presentation with the briefing to the Dutch parlement, it gave me some ideas how the cause of the second wave of infections. This morning, a news report with a statement from the RIVM, affirmed these ideas. It were primarily young adults (18-25 years) who going on holiday to Spain and the south of France during August, who became infected in August. Then at the start of September the infection spread further through parties and student dorms. Through them also their parents got infected and from there is spread further to the nursing homes. The number of infections has been doubling about every two weeks. It is only the last two weeks that the number of hospital admissions has been on the rise. This week is also was announced that about ten thousand people died during the first wave. The average age was close to the life expectancy.

Friday, October 2, 2020


Thursday, October 1, 2020


Wednesday, September 30, 2020

A simple Git workflow

Git is a distributed version-control system for tracking changes in source code during software development. It is probably the most popular system at the moment. But it is also a very complex system, which can be used in many different ways. I also have noted that there is often some confusion about the internals of Git among people starting to work with it. Many introduction to Git, like Learn Git Branching, fail to explain the different workflows of working with it. Below, I present a simple workflow, which works good for a small team.

Although Git is a distributed version-control system, it is often used in a centralized manner, where there is a central repository and where everyone syncronizes work through this central repository. There are free Git repository services, such as GitHub and GitLab, which also provide additional features, such as issue tracking. It is also possible to set up a central repository on a file server using the "git init --bare targetdir" command. The common way of creating a local copy of a central repository is to use the "git clone path", where the path is either a link to a repository on a service or a file path to a respository on a shared file server. Before you start working, you should issue the following commands:

  • git config --global pull.rebase true
  • git config --global rebase.autoStash true

After a local clone of the central repository has been made, you just can start working. By default you are now in the master branch. If you have been working on some issue for some time or you have heard about someone else having pushed a commit to the central repository, you issue the command:

  • git pull
If there are indeed new commits on the central repository, this will stash your changes, pull these commits, and apply the set of stashed differences to the up-to-date state of your local repository. This could lead to merge conflict, which need to be resolved. (There are various tools to resolve conflicts, but I find simply editing the files often the easiest way.) You can repeat this as often as you want.

Now that you are ready to commit your work, your issue:

  • git add files to specify the files you want to include in your commit. This command can be repeated. It is also possible to specify a directory.
  • git commit to create the commit
  • git pull to see if there are some new commits in the central repository that you need to deal with. If this command does not reply that your local repository is already up-to-date, it means that your last commit has been applied to the last commits from the central repository. Then you need:
    • Resolve any merge conflicts
    • Build and test your work. Fix any problems.
    • git add to add resolved merge conflicts and fixes.
    • git commit
    And repeat this step, until there are no new commit pulled from the central repository.
  • git push to push your commit to the central repository.
There is still a chance that between since the last git pull command someone has pushed a new commit. In that case a merge will occur in your history. This merge could have broken the build and/or some tests. It is good to verify if this the case and fix any problems.

Editted text on October 7, 2020

Tuesday, September 29, 2020


At 17:34:46, I bought the book Elsbeth Cochius: Begegnungen / Ontmoetingen written by Elsbeth Cochius and Gert Gerrits in German and Dutch, published by Stichting Programmaraad Beeldende Kunst in 2008, ISBN:9783981069327, from charity shop Het Goed for € 3.50.

Sunday, September 27, 2020

At 9:58, I picked up a chestnut from the Helmerstraat (road) during our walk of this morning.

Saturday, September 26, 2020

Border poles near Coevorden (part 2)

Conny and I continued our search for border poles near Coevorden. We looked at three different locations. Some poles where hard to find due to a lot of over grown. The poles we found are:
  • At 11:36, two poles 132-I.
  • At 12:06, pole 138-I.
  • At 12:17, pole 138.
  • At 12:50, two poles 147-II.
  • At 13:09, only one of two poles 148.
  • At 13:23, pole 148-I.
  • At 13:34, two poles 149.
  • At 13:40, pole 150-I.
  • At 13:54, pole 151.
  • At 13:56, pole 151-I.
  • At 13:57, pole 151-II.
  • At 14:10, pole 151-III.

Tuesday, September 22, 2020

Second wave

It looks like the second wave of COVID-19 infections has arrived in the Netherlands (as well). The number of infection has steady risen in the past weeks. It is only last week that also the number of hospitalizations has gone up. In the past week they have doubled. It is likely that this will continue in the coming weeks. Last Friday some addition regional measurements have been announced. This evening, I watched last Sundays episode of Zondag met Lubach. It explained how the problems with the number of test being available in the Netherlands is related to the choice of the government to have the tests being done by the fifty regional labs, which are tied to hospitals, and not using commercial testing capacity until recently. Hugo de Jonge, the current minister of Health, Welfare and Sport has stated that this was also to sustain the regional labs until after the COVID-19 crisis. The program also mentioned that one of the member of the Outbreak Management Team is the chairman of the Dutch Association for Medical Microbiology, which represents the microbiologist working at the regional labs.

Sunday, September 20, 2020

PARR specification

In the past weeks, I have been thinking about the steps with which a formal specification of the PARR patterns could be transformed into the PARR generator, which I wrote last month. In a way it is also similar to proving the correctness of the program. I have come up with some kind of specification of the collection of all PARR patterns using a made up specification languages where types are defined as sets. There are three types of 'complex' values: list (denoted with square brackets), sets (denoted with curly brackets) and maps (denoted with curly brackets and a colon separating key and value). Sets stands for all enumeratable sets and Nat stands for a natural numbers (including zero).

Graphs = { { "V" : V, "E" : E }
         | V in Sets and
           E subset { { v1, v2 }
                    | v1 in V and v2 in V and v1 != v2 } }

subgraph(G1 in Graphs, G2 in Graphs)
  = G1."V" subset G2."V" and G1."E" subset G2."E"

FullPARRgraph = { "V" : V, "E" : E }
    where { "V" : V, "E" : E } in Graphs
      and V = { [x, y]
              | x in Nat and y in Nat and
                0 <= x and x < 4 and 0 <= y and y < 5 }
      and E = { { [x1,y1], [x2,y2] }
              | x1+1 = x2 and y1 = y2 or
                x1 = x2 and y1+1 = y2 or
                x1+1 = x2 and y1+1 = y2 or
                x1 = x2+1 and y1+1 = y2 }

PARR(nrp in Nat, nrl in Nat)
  = { graph
    | subgraph(graph, FullPARRgraph) and
      size(graph."V") = nrp and size(graph."E") = nrl }

This is not really an executable specification, yet it contains everything to calculate the PARR function.

Thursday, September 17, 2020


Tuesday, September 15, 2020

32.1° Celcius

The temperature at Twenthe Airport went up to 32.1° Celsius, which breaks the previous record of 29.3° for the temperature on this date in 2016.

Saturday, September 12, 2020


November 2020
October 2020
September 2020
August 2020
July 2020
June 2020
Alzheimer's Disease
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