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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
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.
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.
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.
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 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.
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:
- Hmisu in the main room using two
- Acheface in the smaller room
on a large Eurorack modular synthesizer. I danced during most of the
- Jungle of Wires in the main
room with a rather small Eurorack modular synthesizer.
Puzzles by Annabel
In the past months, Annabel developed a set of
eight fractal jigsaw puzzles. Today, she
website where they can be ordered separately or combined.
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.
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.
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 gallary Objektief with works from first
year students from Cross Media from the AKI. I liked the following works:
- The photo essay Lola by Yentil Foks.
- The photo essay Zondag is voor de familie by Maxime Roelink.
- The photo essay Lijnen by Koosje van de Lecq.
- The photo essay Samen spelen, samen delen (as a booklet) by
- The wedding of Harry and Anne Ros (as a booklet) by
- Ik wil mijn broertje opnieuw in elkaar zetten by Emma Dekens.
- Composities by Wouter Hof.
- Cirkel by Iris Veltman. (I indicated interest in buying one of
- Restless Peace (a series of prints tranfered on a long sheet of
paper) by Ralph van Westen.
- Pa ken jij Niek? by Gaby van der Hertog, Christy Lugtenberg, and
Yvanca van Veen.
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
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
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:
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:
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.
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
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.
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
| May 2019
| July 2019