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Diary, June 2019

Sun Mon Tue Wed Thu Fri Sat
  2   3   4   5   6   7   8
  9  10  11  12  13  14  15
 16  17  18  19  20  21  22
 23  24  25  26  27  28  29

Sunday, June 2, 2019

First hot day

Today, the temperature reached more than 30°C in the Netherlands. In De Bilt it reached 30.4°C, which is the highest temperature ever measured on this day of the year, and at Airport Twente it reached 30.9°C, which might as well also be the highest temperature ever measured at that location.

Saturday, June 8, 2019


At 16:54, I bought the book Kunst werkt | Art works with an introduction by Renilde Hannacher-van den Brande, in Dutch and translated to English, published by Peter Stuyvesant Stichting in 1992 from charity shop Het Goed for € 2.50.

Sunday, June 9, 2019

Outdoor art

I first went to Kunst in het Volkspark (Art in the people's park). I found the following things interesting:

Next, I went to KunstenLandschap. At Tetem art space, I met with Willemijn Calis, who was there to show the augmented reality project she had been working on. I left my coat at Tetem, because it had got too warm outside for wearing a coat. I found the following artist worth mentioning (in the order I saw their works):

At location number 25, the farm "de Vèger", I found a copy of the book Stilte, ruimte, duisternis: Verkenning in de natuur (Silence, space, darkness: Exploration in nature) by Kester Freriks. I noted it, because I had just seen an art work with three wooden boxes with the words silence, space and darkness on them. Then someone told me that the book had served as the theme for this year. Somewhere along the route, I took a picture of a wild orchid and a picture of the sky.

Hollow chestnut

When I came home, I kicked against a hollow chestnut, while walking in the garden. It was the first chestnut that I found last year and placed in a pot. It started to grow and I noticed that the chestnut had become hollow. I do wonder how the hollow chestnut ended up on the path and suspect that some animal was involved.

Friday, June 14, 2019

Powers continued

Yesterday evening, I had a look at how the expressions of the powers of (a2 + b2) are related to each other and I arrived at this figure:

   - +
  2   1
   \ + -
    1   2
   - + - +
  2   1   3
   \ + - + -
    1   2   3
   - + - + - +
  2   1   3   4
   \ + - + - + -
    1   2   3   4
   - + - + - + - +
  2   1   3   4   5
   \ + - + - + - + -
    1   2   3   4   5
The numbers in each line, stand for the equations and the '+' and the '-' symbols stand for the variant of the Brahmagupta-Fibonacci identity that has been choosen. The '\' is used when both '+' and '-' return the same result. This happens when one of the squares is zero. If seems that twice taking the same variant, leads to the same result. Lets see if this is generally the case:

(r2 + s2)(a2 + b2) = (rb + sa)2 + (ra - sb)2
((rb + sa)2 + (ra - sb)2)(a2 + b2) = ((rb + sa)b + (ra - sb)a)2 + ((rb + sa)a - (ra - sb)b)2 = (rb2 + sab + ra2 - sab)2 + (rab + sa2 - rab + sb2)2 = (r(a2 + b2))2 + (s(a2+ b2))2

(r2 + s2)(a2 + b2) = (rb - sa)2 + (ra + sb)2
((rb - sa)2 + (ra + sb)2)(a2 + b2) = ((rb - sa)b - (ra + sb)a)2 + ((rb - sa)a + (ra + sb)b)2 = (rb2 - sab - ra2 - sba)2 + (rab - sa2 + rab + sb2)2 = (rb2 - 2sab - ra2)2 + (sb2 + 2rab - sa2)2

Now, it seems that the results are not the same.

Sonic DIY

I the evening, I went to the second edition of Sonic DIY at Sickhouse in Enschede. First Patrick Jonkman gave a presentation about the history of electronic instruments. This was followed by a live performance by Dennis van Tilburg (on SoundCloud). Nicolas from soundforce told something about the Eurorack modules he is developing. It was mostly about a DCO (digital voltage controlled oscilator). After a short break, there were some five minute jam sessions with pairs of people. The jam was hosted by Gijs van Ouwerkerk with Ingmar Kops, Gregor Beyerle, Nicolas Toussaint, and Jasper Schütz. I listened to the first jam, but left the room when it became a little too hot for my tasted. I joined the Live Hex workshop held by Ole Nieling, which was about building a simple oscilator with the CD40106BE, also known as the Hex Schmitt Trigger (with inverter) IC. I build the basic circuit with a LDR and 10nF capacitor. I went on to experiment a little and put two oscilators in series using another 10nF capacitor. There were three more performances:

Monday, June 17, 2019

Puzzles by Annabel

In the past months, Annabel developed a set of eight fractal jigsaw puzzles. Today, she launched her website where they can be ordered separately or combined.

Tuesday, June 18, 2019


At 17:48, I bought the book Art in the office: ING art collection, a universal language written by Consuelo Fernandez-Ruiz in Dutch, published by Waanders in 2006, ISBN:9789040083204, from charity shop Het Goed for € 1.95.

Friday, June 21, 2019


At 17:24, I bought the book The Te of Piglet written by Benjamin Hoff in English, illustrations by E.H. Shephard, and published by Mandarin in 1993, ISBN:9780749315146, from charity shop Het Goed for € 0.95.

Sunday, June 23, 2019


I first went to open day at 'De Zesprong', only to discover that it was offically already over. I met some people that I knew, including Femke Kloppenburg and René Völker. Next I went to XPO to see the exhibition A State of Obscurity by I-Yen Chen. She is from Taiwan. Next, I went to the opening of The Big Discovery at photo gallery Objektief with works from first year students from Cross Media from the AKI. I liked the following works:

Monday, June 24, 2019

Exact Cover complexity

When playing with the puzzles Annabel created, I discovered that the puzzle that I thought was the most difficult, because it had only one solutions and lots of pieces, was actually rather simple. So, this made me think about the complexity of an exact cover. Assuming that you have some strategy for solving an exact cover, you can count how many steps it takes on average to find a solution. Because with the puzzles, some pieces with the same shape can occur more than once, I decided to implement an exact N cover algorithm, where for each position (column) you can define how many 1's it should exactly contain. Each such exact N cover can be rewritten into an exact cover by adding some extra positions (columns) and vectors (rows). After having verified the exact N cover implementation, I implemented an algorithm that uses some randomness to find a solution. The strategy it uses is to find all positions with a minimal number of vectors to be selected and than at randomly select one of the vectors that is involved, taking into account that a vector could be involved with multiple minimal positions. Futhermore, I decided to both counting the placement and the removal of a vector as a step. This algorithm is called repeatedly within a fixed time interval, to find an average. For the puzzles from the first series, the results are presented below. The first column is the name of the puzzle. The second column gives the number of solutions to the puzzle. The third column gives the average number of steps needed to solve the puzzle when running the algorith for 10 minutes. The fourth column gives the pieces that make up the puzzle. The results seems to imply that there is no relation to the number of solutions to a puzzle and the difficulty.

  S1P1  123  36.9   2,2,2,2,3,4,7,9,14,14,34,999
  S1P2   68  68.0   2,2,2,3,4,4,7,9,12,14,34,999
  S1P3   18  34.0   2,2,2,2,3,4,4,7,14,34,38
  S1P4    8  35.6   2,2,2,2,3,4,13,14,15,33,34
  S1P5    3  84.5   2,2,2,3,4,4,8,9,14,15,34
  S1P6    1  22.5   2,2,2,2,3,3,3,3,4,4,12,14,33
  S1P7    1  24.2   2,2,2,2,3,3,3,4,4,4,7,10,14
  S1P8    1  28.8   2,2,2,2,2,2,3,3,3,3,3,3,4,4,5

Tuesday, June 25, 2019

Hardest Fractal Jigsaw

During the night, I let the program run over all of the possible puzzles (with pieces up to size five) for just one second, to discover what might be the hardest Fractal Jigsaw puzzle. The running time was 1 second. Then in the morning, I ran the top ten with half a minute runing time. This resulted in:

  1336   2,2,2,2,2,2,2,2,3,3,3,4,14,15
  1229   2,2,2,4,4,4,9,9,12,14,15,999
  1173   2,2,2,2,2,2,2,3,3,3,3,3,3,4,9,999
   981   2,2,2,2,2,4,4,4,8,9,9,18,999
   954   2,2,2,2,2,2,2,2,3,4,4,9,142,999
   944   2,2,2,2,2,2,2,2,3,3,3,3,4,38,999
   928   2,2,2,2,4,4,4,9,12,18,38,999
   913   2,2,2,2,2,2,2,3,3,3,3,4,9,34
   838   2,2,2,2,2,2,3,3,3,3,3,4,12,14,999
   832   2,2,2,2,2,2,2,2,3,3,3,3,4,4,9

It is suprisingly, how many of these have the 999 piece, which is the smallest possible piece. In the evening, I also looked for the easiest and hardest puzzles that can be made with the pieces of the first series that Annabel made. The hardest is 2,2,2,2,2,2,3,3,3,3,3,4,12,14,999 in the above table. Some of the easiest are:

  13.0  2,2,2,3,4,7,14,14,34,38,999
  13.0  2,2,2,3,3,4,12,14,14,33,34
  13.1  2,2,2,2,3,3,14,14,15,33,34
  13.4  2,2,2,4,10,13,14,15,33,34,999
  13.5  2,2,2,2,3,3,3,4,13,14,33,34
  13.6  2,2,2,3,4,12,14,14,34,38,999


Today, the temperature reached 25.3°C at Airport Twente. This is the first time that the temperature reached this high this year and probably also on this date since the temperature is measured at this location.

Friday, June 28, 2019

Finals 2019

This afternoon, I went to the AKI finals 2019 exhibition at the AKI building. I found the works of the following graduated students noteworthy (in the order I encountered them):

At 18:38, I bought the catalog Developments 18/19 edited by Johan Visser, written in Dutch and English, and published by AKI Academy of Art & Design on Friday, June 28, 2019, ISBN:9789075522402, for € 10.00.

Saturday, June 29, 2019

Warmth record

Today, at Airport Twente a new warmth record for this date was broken with 32.8°C. The previous record was 32.3°C from 1957. In many parts of Europe warmth records were broken.

This months interesting links

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