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FC Twente
Today, it was the final day of the Dutch Eredivisie soccer competition. F.C. Twente '65 took the first place on the ranking
and with their 2-0 score against NAC Breda they secure the victory of the competition. And the
city went wild. People were adviced not to come to the city center.
The last game was played in Breda, but both in the station and in
the city center large video screens were installed. In the evening,
the A1 motorway was blocked by fans who wanted to honour the
players on their trip home.
Tomorrow afternoon, there will be a large celebration from a parking
lot visible from my office at work. I am expecting to get some trouble
trying to go home.
Update: before and after the game report by RTV-Oost.
Samsung NC10 netbook
This evening, I went to collect a Samsung NC10 netbook, which I bought secondhand from a
private person for € 200. I want to bring this with
me on our trip to China this summer.
Four years ago, I had already felt that we should have brought
our own laptop. Yesterday, I transfered the money by bank and
included the serial number in the remark. When the bank statement
arrives I will take it with me as a proof that I bought the netbook.
Final report about Flight 1951
Today, the final report about the crash
of Turkish Airlines flight 1951 on Wednesday, March 4, 2009 near Schiphol, Amsterdam was released.
This report gives a number of interesting additions to the earlier
reports, and puts, in my view, more blame on the pilots than the
Prelimenary report.
The report states that the pilots should have executed a
go-around, because they did not finish the landing checklist
in time. One of the reasons for them not finishing the checklist
in time, might have been that the Air Traffic Control but them
on a shorted approach which caused them to arrive at the glide
path at 5.5 NM with an altitude of 2000 feet, which is too high.
(It should have happened at a minimum of 6.2 NM.)
The report also states that the pilots should have been able
to control the plane when the stick-shaker was activated. The
report states:
Simulation studies and piloted demonstrations showed that
recovery from the point of stickshaker was possible if conducted
in accordance with the non-normal procedure published by Boeing.
Further, simulation studies showed that recovery was possible
even if thrust application was delayed up to 9 seconds after
stick shaker, provided that pitch was controlled to prevent a
full stall.
As a side remark, the Dutch version of the report contains some links to the
Dutch Wikipedia in section 2.2.7 "Overtrekwaarschuwingssysteem"
on page 24 and (where the text seems to be copied from) the list
of concepts ("Begrippenlijst") on page 95.
Update, May 20:
At 19:34:15, I bought the book Informatica aan de THT (Computer Science at the University of Twente)
geschreven written by Wiek Vervoort (ISBN:9789036523547) for 15 Euro from
De Slegte. One of the reasons I bought
the book is the fact that my name is mentioned on page 11 of the third
part as one of the 51 students that got their freshmen diploma's. But
also because of the many stories and pictures of people that I know.
I studied at the university for four and half year and worked there
for about seven years, which means I spend more than eleven years at
the university.
Going into the city
Today, Li-Xia and I went into the city. After we
did our normal shoppings at the open-air market, we went to
Beune Optiek to look for a new
pair of glasses. First my prescription was checked, and as I had expected,
it was still the same as ten years ago. When
we were looking for a frame, Annabel arrived.
After much consideration we selected a Zeiss frame. I am going to have
Clarlet 1.74 AS glasses with a refraction index of 1.74, which is
higher than the the 1.67 that I have now. Annabel also had her eyes checked
and the result was that she had perfect vision.
Annabel left us, and we walked to bookshop De Slegte
where at 14:46:40, I bought the following three pockets for € 5:
- Een spion in het huis van liefde (A Spy in the House of Love)
by Anaïs Nin. ISBN:9789035115743.
- Lieve vogeltjes (Little birds) by Anaïs Nin.
ISBN: 9789035115439.
- Het feest der liefde van Ronald Giphart. ISBN:9789041700872.
We crossed the road and went to bookshop Broekhuis.
There I found the book Enschede Verrast with pictures in and around
Enschede (ISBN:9789090251523). I decided to buy the book as a gift for our
family in Urumqi, China. At 15:02:34, I bought the book for € 17.50.
When we were home, I remembered that I should have had my passport photos taken
for our visa application for our trip to China.
I went back to the city and got them from Fotostudio Christy.
Barcelona trip
Last Thursday, we left around 2 o'clock in the night with about
seventy people on a trip to Barcelona
to celebrate that company I work at existed ten years. During the
security check I was given the option to check-in my backpack or
give-up the Postbank multitool I was carrying.
I decided for the last. We took-off at 6:10 from Dusseldorf Airport
and landed at 8:03 in Barcelona. We flew with flight AB8936 from
AirBerlin in the D-ABBO, a Boeing 737-86J. We were assigned the seats 25C (Li-Xia)
and 22E (me) but we took seats 25E (Li-Xia) and 25F (me). In
the morning we made a but tour through the city bringing short
visits to mount Montjuïc, Sagrada Família, and Park Guël.
In the hotel we got a Plano de Barcelona map.
In the afternoon, we slept some time and in the evening we went
into the city. First we ate something at the restaurant at the
top op Le Corte Ingles. (At 17:18, I paid €6.60 for two
"Bolleria vari", one "Te", and one "Z.Melocoton".) Next we
walked around over the Ramblas to the old harbor. We climbed
the Columbus statue. At 18:38:50 we bought to tickets, € 3
each. We had some drinks and dinner on Plaça Reial.
The drinks we got (at 18:22) from Restaurant Taxidermista.
On Friday, we took a walking tour through the Gotic District.
Afterwards, we visited Llibreria del Museu MACBA. Around 12:50, I bought the Barcelonès i el seu entorn map from a bookshop
along the La Ramblas for € 6.50. In the afternoon, we
went to the Sagrada Família. At 13:55 we bought our tickets
for € 24.00. Later we took the elevator and bought two
tickets with the numbers 095003 and 095004 for € 2.50 each.
On Saturday, we took a biking tour, but we had to abandon this
early. In the bookshop Sant Jorge on Carrer Ferran 41, I
bought a French/Dutch version of Antoni Gaudí: The
Complete Works ISBN:9783836511643 for € 9.99.
At 13:05:30, I got € 50.00 from a cash dispenser
from La Caixa bank.
We also went to the Casa
del libro bookshop, where I considered buying the Spanish
(I presume) version of Tractatus Logico-Philosophicus.
On the way back we came accross the Bertrand bookshop, which in the back had a nice view to
a small garden. At 15:43:16, I bought Diccionari Català-Anglès -
English-Catalan Dictionary ISBN:9788441225732 for € 7.80.
I also found several advertisements for Dojo Zen Barcelona Kannon and tore-off a small paper with the URL
and telephone number from one of the advertisements.
In the evening we flew back. We took-off at 20:40 and landed at 22:28
on Dusseldorf Airport. We took flight AB8565 with AirBerlin in the
D-ALTD, a Airbus A320-214. We were assigned the seats 25C (Li-Xia)
and 24F (me) but Li-Xia took seat 24E.
This KML file, which can be
viewed with Google Earth, gives
information about our movements during our stay in Barcelona.
Boolloop
Lately, I have been thinking about a language that only
has Boolean values (true or false) and loops. For this
reason I gave it the provisonary name Boolloop.
Because the language does not allow the definition of (recursive)
procedures and all loops are of fixed length, the complexity
of any program in this language is polynomial and can be
calculated (in polynomial time) by simply analyzing the
structure of the program. I believe, that the language is
also Turing complete for Turing machines with polynomial
complexity. I am still not sure about which kind of statements
will be included. The language will have multi-dimensional
Boolean arrays. I am not sure if it will include an if-statement,
because maybe it is not needed. I am also strongly thinking
about only having parallel assignment statements together
with "any" and "all" expressions. The idea for this language
came while thinking about the P versus NP. I am not sure whether resolving the
P versus NP problem with the Boolloop language (instead of
Turing machines) also resolves the original P versus NP
problem.
Into the city
Today, Li-Xia and I went into the city to do some shoppings.
At Media Markt we looked
at some pocket camera's. This summer, Annabel wants to bring a
camera with her as well. So, I thought it might be a good idea
to buy a new digital camera to bring with us to China. I made the following selection
of camera's that I want to investigate further:
- GE A1250. Just costs € 59
- Samsung ES 65 for € 99
- Canon A3100 for €119
- Panasonic DMC TZ28 for €239
We also went to bookshop De Slegte
where I exchanged my extra copy of Buiten is het Maandag for
a copy of Hemelvlucht (Sky burial) by Xinran to be given
as a present. It was some weeks ago, that I discovered
that I had bought two copies of the book Buiten is het Maandag.
I did so on Saturday, April 3 and
Wednesday, April 14.
This afternoon, a Postbank Multitool arrived through the mail
and I started carrying it in my bag.
Thursday, May 13, I was forced to hand in such
a multitool because I was not allowed to take it has hand luggage
into a plane and because I didn't want to check-in my backpack.
On the page
Corkscrews for Sale from Donald Bull's Virtual Corkscrew Museum I found a nice image of this tool. He is asking $45 for such a tool.
On marktplaats.nl, I found
someone willing to sell one for 10 Euro including the orginal box
in which it came. I decided to buy it.
Books
Today, Li-Xia and I went to the birthday party of Bert. I gave him the book Hemelvlucht (Sky Burial) by
Xinran (which I bought last Saturday) as a present. I
also lend him the book Perfect Rigor and in return I borrowed the
book The Poincaré Conjecture
by Donal O'Shea. At home I started reading
the book, which also speaks about Perelman.
In the past weeks I have been studying the paper Faster Solutions for Exact Hitting Set and Exact SAT by
Limor Drori and David Peleg. The Exact Hitting Set (XHS) problem is
basically the same as the Exact Cover
problem. It is just another way to formulate it. I have studied
the paper because the Exact Cover problem is NP-complete and thus
relevant for the P versus NP problem.
So far, I have only studied the first six pages in detail.
I have found a number of small mistakes. I think that on page 3 in
the first definition of COLLIDE there should read
j: i,i' (instead of j,i,i') after the existential
quantifier, just like in the second definition. COLLIDE
can also be defined as the union of all Rj' with
j' in Ci excluding either {i} (for
the first definition) or Rj (for the second definition).
I am also getting the impression that Ci was first
defined as Ri, because on page 6 and 8 we encouter
expressions like Ri\Ri' where I
think it should read Ci\Ci'.
After studying the cannonizing algorith on page 5 and 6, I conclude
that (e), (f), and (g) are basically the same. The idea is that a
row cannot be selected, it after selection it leaves an empty column
(a column with no 1). If a row is selected, all the rows that collide
with it are also removed. An empty column arises when the row collides
with all the rows of that column, or in other words: A row i can
be eliminated when there is a column j such that i not in
Rj and Rj is a subset of
COLLIDE(i). This is exactly what it says in
(f), at least if (as I understand it) "each row in Rj
overlaps row i" means that each of these rows collide with row i.
If, as stated in (e), Rj1 is a subset of Rj2,
then it is true that for all rows i in Rj2 but
not in Rj1, that row i is not in
Rj1 (by definition) and Rj1 is a subset of
COLLIDE(i), because Rj2
is a subset of COLLIDE(i) extended with i.
For the first case of (g) it is true that column j' is not
in Ci2 (remember that in the text it says incorrectly Ri2).
The fact that row i1 is in Rj'
implies that Rj' is a subset of COLLIDE(i1).
And because COLLIDE(i1;j) equals
COLLIDE(i2;j) it means that
Rj' is a subset of COLLIDE(i2)
as well. Which means that condition (f) is satisfied.
I was surprised by the fact that the recursive algorithm presented in
paragraph 2.4 on pages 10 and 11 always selects the column with
the largest set of matching rows. The idea behind this is that whenever
you select a column with a large number of matching rows, a large
number of rows are eliminated when each of the possible rows is
tried, meaning that the problem space is reduced the strongest.
The remainder of the paper goes on to show the number of rows that
are eliminated for many columns with low number of matching rows.
And this is then used to formulate an exponentional upper bound
of the algorithm. The algorithm that I have developed so far,
always selects the column with the lowest number of matching rows.
It also only implements case (e) for the impossible rows elimination.
I did implement case (f), but it showed, in the kind of Exact Cover
problems that I tried, not to result in a speed-up. I tried to
implement the strategy of selecting the column with the largest
number of rows, but it did not find a single solution within half
a day for the Beat the Computer No. 24
Exact Cover problem. But that still does not prove much. Maybe the
strategy of selecting the column with the largest number of matching
rows works beter on average or for complex Exact Cover problems
with few solutions. But if it is the case that the strategy of
selecting the column with the least number of rows is better, this
could mean that there is even a better upper bound on the Exact Cover
problem.
Visas
Today, I received an email from VisumBuro that have collected our passports from the
Chinese Embassy. It looks like we did receive our visas
for our trip to China.
I wondered if finding an Exact Cover knowing that there is only one solution,
is still an NP-complete problem. Sometimes an additional
constraint can make a problem much easier to solve. My gut
feeling says that it is still an NP-complete problem. If
one could proof that the Single Solution Exact Cover (SSEC)
cannot be solved with a polynomial algorith this would proof
that NP is unequal P. So,
actually there is no need to proof it. Then I realized that
solving the Difficult Exact Cover problems that I described on
April 23 is equivalent to the
problem of finding n vertices in a connected graph
given the condition that no two selected vertices are connected
with an edge. The graph has one vertex for each row and
an edge is created between to vertices if the rows have a
matching column. Actually, this kind of Exact Cover problems
have some additional constraints, namely that each row has
the same number columns set, which could be an additional
reason for it not being NP-compelete. Finding such a subset of
vertices in a graph is known as the Indepedent set problem. If I understand it correctly,
finding an independent set of a given size is an NP-complete
problem. If this is the case, it seems that the SSEC problem
is also NP-complete. Because finding an independent set is
related to finding a clique in the inverse graph, the problem
is equivalent with finding a clique of fixes size.
Suitcase
This evening, at 19:42, I bought a Kingston suitcase
from the LIV-collection for € 89.06 from
V&D. I bought it
for our China trip.
I found some interesting material by Scott Aaronson, which gives me the feeling I haven't understood
much of the P versus NP problem.
First of all there is the powerpoint presentation
Has There Been Progress on the P vs. NP Question?, which
was used for a talk on Barriers in Computational Complexity
workshop, Center for Computational Intractability, Princeton
University, August 25, 2009. Then is there the paper
Algebrization: A New Barrier in Complexity Theory by
S. Aaronson and A. Wigderson, which appeared in ACM
Transactions on Computing Theory 1(1), 2009. And also an earlier
paper Is P Versus NP Formally Independent? by Aaronson, which
appeared in Bulletin of the EATCS 81, October 2003. Lots of
material to study, I think.
Katla about to erupt?
Today, there has been some news that Katla is about
to erupt. In the past days, I already noticed some
interesting things about the tremor plots.
If you look at the tremor plot from April 13 till now, you see that there
is an increase for the stations "hvo" and "hau" since the
graph for the other stations remained almost dead since
around May 22. But on the tremor plot of the last day you see that all stations
pick up the same signals. This could be explained by the fact
that the first graphs are scaled to the maximum tremor signal
originating from Eyjafjallajökull eruption, and that the
tremors we see now originate from another source. I think, that
other source could be Katla. The letter "hvo" seem to point
at the station "Lágu-Hvolar" which is on the otherside
of Katla from Eyjafjallajökull.
It is a fact the last nine major historical eruptions of Katla
all occurred during the summer period. I am worried that this
might an effect on our trip to China.
If the Katla erupt before July 12, we probably will cancel our
trip. If it happens before July 29, and airtravel is obstructed
for more than a week, we probably have to travel back by train
through Almaty, Kazakhstan and Moscow.
Going into the city
This morning, I went into the city for shopping. I also went
to bookshop De Slegte. I saw
a little book with the title Instructie Electrische locomotieven
Serie 1300 about the NS Class 1300 electrical locomotive, with
detailed electrical schema. It costed € 17.50. I did
not buy it. I also saw a book about the inventory of
Johan Huizinga.
At 11:02:17, I did buy the CD Language Passport Nederlands
Chinees by BABEL BV for
€ 3.99. The CD also contains MP3 files and there is
a small booklet with the whole text and some additional grammar
in the case. I think I am going to listen to it the coming
weeks, and hopefully learn some more Chinese in preperations
for our trip.
Next I went to Beune Optiek to get my new pair of glasses. Annabel did
not like the frame we had selected, so, I went back and looked
at some other frames. Last Tuesday, Annabel and I made our
final selection and decided for a Ray Ban frame with the number
RB6160 2531 50-19 135 (in which the dash stands of a little
square). As usual, I was quite surprised how sharp everything
looked with the new glasses. My eyes and brain did not require
much adjustment to the new glasses. My nose and ears (or actually
behing my ears) have more problems.
(The bill. At 11:14:04, I paid the
€ 597.00)
De Slegte
This afternoon, I went back to bookshop
De Slegte to have a second look at Instructie Electrische
Locomotieven Serie 1300, which I saw last
Saturday. At 17:50:38, I bought this book for € 17.50.
I think it is a good price, because I think this is a very rare book.
At home, I could not find anything about it on the internet.
This months interesting links
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