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Dairy, May 2010



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Sunday, May 2, 2010

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.


Monday, May 3, 2010

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.


Thursday, May 6, 2010

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:

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:

De Slegte

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.


Saturday, May 8, 2010

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:

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.


Sunday, May 16, 2010

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.


Thursday, May 20, 2010

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.


Saturday, May 22, 2010

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:

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.

Postbank Multitool

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.


Monday, May 24, 2010

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.

XHS paper

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.


Wednesday, May 26, 2010

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.

Single Solution Exact Cover

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.


Thursday, May 27, 2010

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.

P versus NP

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.


Friday, May 28, 2010

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.


Saturday, May 29, 2010

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.)


Monday, May 31, 2010

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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