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Chestnut
Around half past nine, I picked-up a small chestnut at Wilminkweg, just outside of Enschede. It looked shinny dark brown when I
picked it up, but in the afternoon, when I put it on my desk, it had turned
light brown.
At 11:02, I bought the book De Voedselzandloper (The food
hourglass) by Kris Verburgh
(ISBN:9789035137585) from bookshop Polare
for € 17.95. In the evening, I paged through it a little.
Palindrome date
Today is a palindrome date when
written according to the (D)D-(M)M-(YYY)Y format: 3-10-2013. The
previous such date was October 2, 2012
and the next will be ctober 4, 2014.
GPS game
Today we had our 'summer' outing of our company. We went to Deventer and in
the afternoon we played a GPS game, where we were given a GSP tracker with
24 marked locations. We were also given a sheet with 24 photo's taken at those
locations and given the task to pair them up. During the game some extra
assignments where given. There also was a challenge area where you could
earn extra points by doing some games in the categories: think, dare, or
do. For the think game, I solved three tangrams and for the dare game, I
comsumed one fried locust. Our team became thirds from the eight teams.
In the evening at home, I reconstructed the route we took bases on my
memories with Google Earth:
KML file or
in Google Maps.
Second visit to Peter Struycken
I went to visit Peter Struycken again. He
allowed me to investigate his personal archive with respect to his
(non-commisioned) work. I even could take a part of his archive home to
continue my work on compiling a list of his works. (See this page for the results of my ongoing research.) He also gave my a USB
stick with all the digitized images of his works he has collected. (He has
given me permission to publish these images in the context of my research.)
In the past weeks he spend some effort to digitize the many slides he has.
He has become quite interested about my research, and after I showed him
some of the information that the Groninger Museum has online about him,
we thought it would be a good idea to make an appointed to visit the depot
and investigate all the information they have about him. They have a large
collection of his work and he also donated some of his studies to the
museum. I could also take some books (invitations) home. These are:
Books
At 9:35, I bought two books from bookshop
Polare. Yesterday morning, I already decided to buy these books, but I
did not have a suitable bag with me. The two books are:
- De Avonden
- Een Beeldverhaal by Gerard Reve and Dick Matena,
ISBN:9789023410560, for € 9.95.
- How the Universe Got its Spots door Janna Levin,
ISBN:9780691096575, for € 13.50.
This afternoon, I finished reading the book
Mathematical Vistas: From a Room With Many Windows by
Peter Hilton,
Derek Holton, and Jean Pedersen, which I started reading on
September 14 the day I bought it from
bookshop Polare. I have to admit that I did
not read every letter of it, and many times, I did not really try to grasp
what it said. I book like this would require many hours of serious study to
complete understand every part of it. Still, I found it an interesting
read. It surely did made me think about the Four colour theorem for many hours, and it still does.
Grafiek+
This morning, I discovered that some prints by Peter
Struycken were on display at the Grafiek+ exhibition at the university. These are works owned by Rijksmuseum Twenthe. They were on display in the building "De Spiegel".
Around one o'clock I went there and saw the following prints:
Gravity
This evening, I went to see the movie
Gravity together
with a colleague. To me the experience of this movie was spoilt by some of the
great physics errors that you do expect in a SF movie like "Star Trek" but not
in a movie like this, which attempts to be realistic. For some explaination read:
Bad Astronomy Movie Review: Gravity.
Warm day
This morning, I went walking with Li-Xia (in a wheelchair) in the Eco park.
I played with the marble track on the artwork
Haakse Haas, I found a green marble while searching for one of my own
marbles (which I did find later). I decided to keep it and carry with me.
At 13:23, I took a picture of the sundail on the
Old Church at the city center, which at noon, can show the approximate date.
Unfortunately, the sun was not so bright, so the shadow of the sundial is not
really sharp.
In bookshop Broekhuis, I looked at the
exhibition on the third floor, which was part of the month of the print. I did
not see anything interesting. At 13:44, I purchased a black, hardback Moleskine
Daily Diary / Planner of 2014 (ISBN:9788866135647) for € 16.95.
At Galerie
Objektief, I met with Wil Westerweel, whoes pictures were on display. I gave
me a free CD with many of his pictures. Hence, I went to
Rijksmuseum Twenthe to see the exhibition Paths to Paradise because I discovered that it included four works
by Peter Struycken. It took me some time to
locate the four works, because the works were ordered by theme and works
for very different ages and thus from very different styles, where combined.
I found it a little odd to find the highly abstract works by Struycken
between figurative works. I also looked at the "Please do not touch. Even
clean hands can damage." installation by Annelies Doom. It consisted of the small shelfs attachted on the wall.
The first had two white cloves to handle valuable objects, and the remained
shelves had one book for evey word, where the thickness of the book seems
to be related to the emphasis given to the word. The book for "not" was the
thickest. From the fact that some of the soft covers had curled-up, it seems
that the books had been touched. (Later, at home, I discovered that the nine
books had an ISBN, namely: 9789461902405, and were published by Uitgever Digitalis.
but it's not available.
I also looked at the exhibitions
Bart Hess. A Hunt for High Tech, which I did not find interesting,
and Renie Spoelstra. Het dode
punt van de schommel, that I found intriguing after I understood the idea
and process by which the works were made.
Finally, I went to Tetem art space, where I
looked at Hybrid Skins and
100 jaar grafiek uit ene particuliere collectie
(100 years of prints from a private collection).
Sequence A056353
I wrote a program that produces the sequence
A056353. The program calculates the number of sequences consisting of 0,
1, and 2, such that the sum is a multiple of 3. Furthermore, sequences that
are rotated, reversed, or have 1 and 2 exchanged, are considered the same.
The sequences for the first number of length are:
- 0
- 00 12
- 000 012 111
- 0000 0012 0102 0111 1122 1212
- 00000 00012 00102 00111 01011 01122 01212 01221 11112
These sequences are related to the Four colour theorem.
Two more sequences
I continued working on the program working on
sequences of 0, 1, and 2. I suspected that the sequences can be divided in
two groups, namely those that can be generated from the sequence 00 and those
that can be generated from the sequence 12. By generating, I mean a process
of replacing two digits of a sequence by three, by inserting 0 in the middle
and either adding 1 or 2 to all three digits (modulo 3). For example, given
the sequence 0012 we can generate another sequence by taking 01 from this
sequence, insert 0 in the middle (resulting in 001) and add 1 to each of them
(resulting in 112) and replace the 01 in the original sequence with it,
resulting in 01122. Sequence 01122 can thus be generated from the sequence
0012. It is clear that any sequence consisting three or more 0 cannot be
generated from either 00 or 12, because in each generation step, there is
always either a 1 or a 2 inserted. The program shows that it is indeed the
case that the sequences that can be generated from 00 and 12 do not overlap
for all sequences with length up to 14. I haven't found a mathematical proof
that this is the case for all sequences. This leads to two sequences that
are related to sequence A056353. It is
remarkable that there are much fewer sequences that can be generated from
00 than from 12. The table below is taken from the output generated by the
program
all 00 12
3 3 1 1
4 6 2 3
5 9 2 6
6 22 8 13
7 40 10 29
8 100 33 66
9 225 57 167
10 582 168 413
11 1464 366 1097
12 3960 1061 2898
13 10585 2646 7938
14 29252 7514 21737
Even more sequences
After some puzzling, I constructed the following transition table:
0 1 2
a b c d
b a e f
c g h i
d j k l
e l j k
f h i g
g c d b
h f a e
i k l j
j d b c
k i g h
l e f a
Given a sequence of 0, 1, and 2, the above table can be used to calculate the
value for the sequence, by starting with 'a' and calculate for each element in
the string another value by using the above table. Now it appears that whenever
you end with 'a', that the sequence is a sequence that can be generated from
00. For sequence generated from 12, you get one of 'b', 'i', or 'k'. I guess
it will not be very difficult to prove this, by the effect of rules for
replacing two digits by three digits in the generation step. Below the table
extended with the number of sequences ending at the given letters:
all 00 12 'b' 'i' 'k'
2 2 0 1 0 1 0
3 3 1 1 0 0 1
4 6 2 3 1 1 1
5 9 2 6 2 3 1
6 22 8 13 4 6 3
7 40 10 29 12 8 9
8 100 33 66 19 23 24
9 225 57 167 60 56 51
10 582 168 413 146 135 132
11 1464 366 1097 370 361 366
12 3960 1061 2898 951 984 963
13 10585 2646 7938 2714 2611 2613
14 29252 7514 21737 7226 7255 7256
15 80819 20209 60609 20285 20189 20135
16 226530 57233 169296 56520 56426 56350
17 636321 159080 477240 159376 158879 158985
18 1800562 451928 1348633 449392 449753 449488
19 5107480 1276870 3830609 1278053 1276311 1276245
When studying the transition one can see that each column has all the letters
from 'a' to 'l' exactly once, meaning that they are permutations of each other.
It is well known fact that any set of permutations is related to a
finite group. The
table can be used to construct the following group (with 12 elements):
* 0 12 21 22 01 10 1 11 20 02 2
0 * 21 12 10 1 22 01 20 11 2 02
12 21 * 0 1 10 01 22 02 2 11 20
21 12 0 * 01 22 1 10 2 02 20 11
22 01 10 1 2 20 11 02 12 0 21 *
01 22 1 10 11 02 2 20 0 12 * 21
10 1 22 01 02 11 20 2 21 * 12 0
1 10 01 22 20 2 02 11 * 21 0 12
11 02 2 20 21 12 0 * 1 22 10 01
20 2 02 11 12 21 * 0 01 10 22 1
02 11 20 2 0 * 21 12 22 1 01 10
2 20 11 02 * 0 12 21 10 01 1 22
In this table '*' stands for the empty sequence, and it also happens to be
the identiy element. This is the
Alternating group
A4, because it is the Von Dyck group with, for example, a is 12, b is 10,
c is 02 and a2 = b3 =
c3 = abc = e.
(See also: Alternating group A4 (tetrahedron) Cayley graph and table.)
Transition graph
I made this drawing of graph representing the transition
table I constructed over the weekend. The arrows with the red triangle
are the transitions for 1, and with the blue triangle the transitions for 2.
The light grey lines, connecting opposite points, represent the transitions
for 0 in both directions. The green lines represent some transitions for 211
or 122 and the purple lines for 221 or 112.
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