Diary, March 2005

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Tuesday, March 1, 2005

Dry snow

This morning, the temperature was -2.5 degrees Celsius. There was already some dry snow on the ground. Throughout the day we got some more dry snow, which was easily blown away by the wind, leading to all kinds of patterns on the ground. But the snow did not melt away like in the past weeks.

Wednesday, March 2, 2005

Heavy snow fall

Yesterday evening, heavy snow fall was forcasted for the Northern part of the country. When I looked outside of the window this morning, I concluded that we did not get any of it. On the news we heard that just 100 Km North of us, they got 30 to 50 cm of snow fall in the last 24 hours. But maybe we still get some later this day, because the small low pressure area causing all of this snow fall is drifting to the South a little.

Later during the day it started to snow again. At first the snow did not stay on the ground, but I guess that by midnight there was at least an inch of fresh snow.

Latin Squares

This evening, I explained to Annabel what a Latin Square is. First I let her make one of size three. Then when she understood it, I asked her to complete one of size nine, where I already had filled in some random squares. I told her that it was difficult, but she still wanted to try it. Last week, I read how Carla P. Gomes had come up with some clever idea how to solve these. She has a nice demo to explain it. I immediately had to think about the Eternity Puzzle and how it was solved. I think that the general approach to solving this kind of puzzles is to choose that next step that will leave as many possible next steps open. In that way your chance that you have are making a "wrong" choice is minimized. (See also my page on Discrete Piece Fitting Puzzles.)

(follow-up)

Thursday, March 3, 2005

Beautifully white

When I looked out of the window every thing was beautifully white with snow. All the trees and plants were covered with a layer of snow and the ground was completely covered.

Friday, March 4, 2005

Very cold

This morning, our outside thermometer showed -6.1 degrees Celsius. In some other parts in the Netherlands (about 100 Km to the North-West) the temperature dropped till -20.5 degrees Celsius. This is the coldest day in March every recorded in the Netherlands. The drop in temperature is caused by a combination of a clear sky, the absence of wind, and a fresh layer of snow.

Saturday, March 5, 2005

Solution to the Latin Square

Today, I spend some time to write a progam to find a solution to the Latin Square puzzle that I gave to Annabel last Wednesday. This evening, she said she was going to find the solution within one hour. Less than a quarter of an hour later, she found the solution below:
```7 6 3 2 9 8 5 1 4
6 9 7 5 4 1 3 2 8
3 4 2 7 8 6 9 5 1
9 8 1 6 5 4 2 7 3
4 2 6 1 3 5 8 9 7
8 5 4 3 1 2 7 6 9
2 1 8 4 7 9 6 3 5
5 7 9 8 2 3 1 4 6
1 3 5 9 6 7 4 8 2
```
The red numbers are the number that I had filled in at random.

Just a little later, I found some obvious improvement for my program. When I implemented it, the program found a solution without performing any back-tracking. The first solution it found was:

```8 4 2 9 5 7 3 6 1
6 7 3 5 9 8 1 2 4
3 5 1 2 4 6 7 9 8
7 9 6 8 3 1 2 4 5
4 2 8 1 7 3 9 5 6
9 6 5 3 1 2 4 8 7
2 1 7 4 8 5 6 3 9
5 3 4 7 6 9 8 1 2
1 8 9 6 2 4 5 7 3
```

(follow-up)

Sunday, March 6, 2005

Snow again and curly kail

Around eight o'clock in the morning, it was 4.2 degrees Celsius below zero. Also in the car it was very cold, and I decided to put on my gloves. There are still some patches of snow left from the snow that fell in the past week. Around noon it was about one degree above zero. Later in the afternoon it started to snow, but because it was already above zero, the snow immediately disappeared when it fell on the bare ground.

Around three o'clock I decided to prepair the curly kail hotchpotch, with the idea that I would have some time left before dinner. Pealing the potatoes was not so easy. But then I discovered that the quality of the curly kail was not particularly good. It had a lot of sand a brown leaves and there where it had been cut, it had turn brown. Cleaning it, took a lot of time. I guess I would have been better of if I had bought the more expensive curly kail from the supermarket instead of going for the cheap curly kail from the open air market, especially this late in the season. I did end up watching some television but that was only because Li-Xia gave a hand.

Monday, March 7, 2005

Software patents endorsed by European commission

It seems that the council presidency adopts Software Patent Agreement against Council's rules. This means that EU ministers endorse patent law that support software patents, although the European parliament and many national parliaments have protested against this. It seems that today is really a black day for democracy in Europe. We will see what will happen at the second reading at the European parliament. It looks like we now live in the Banana Republic Europe.

Tuesday, March 8, 2005

Latin Squares

The program that I wrote last Saturday for solving Latin Squares does generate many double solutions. Today, I discovered a simple adaptation that only generates unique solutions. This version of the progam finds the first 100,000 solutions and prints them one on each line, using one character per square.

I am thinking about implementing an Exact Cover algoritm using the same heuristic. I am thinking about making use of dancing links. It is very easy to see that Latin Squares can be mapped to Exact Cover problems, once you realize that a Latin Square can be transformed into a binary cube, where the value placed in each square is seen as number of the bit that is set in the z-axe. For each direction of the cube there should be exactly one bit set in each "square". So an Latin Square of size n (with no additional restrictions), can be transformed into a exact cover problem with 3n2 positions and n3 vectors. This also shows that each Latin Square can be transformed into 23 equvalent Latin Squares, some of which may be the same as the original.

(follow-up)

Wednesday, March 9, 2005

Three games against Ton

This evening, I played three games of Go against Ton. The first game, Ton was given an eight stone handicap. And besides one small correction at the end of the game, I won the game. With the second game, where he got a seven stone handicap, I gave up after about twenty moves, because I lost a whole corner. We decided to play another game just for the fun, where he was given an eight stone handicap again. I played this game very intuitively, meaning that I did not really spend time to think about the consequences of my moves. In the beginning we played a lot of territorium exchanges. I felt I was losing. Then somewhere in the middle game, I missed an easy way to save a large black group of mine, because I did not see a possibility for a cut. I did not even see it when Rudy remarked that it was there. Because Ton had finished his beer, he gave up. He remarked that I was slowly getting stronger and that it would be possible that I could jump several ranks in the coming year.

Thursday, March 10, 2005

Test results

Two weeks ago, Annabel did some IQ test (I guess WISC-R), and last week she did a dyslexy test. Today, the results arrived in the form of a letter. According to the test, her average IQ is 113, better than average, but not really exceptional. But according to the test her performance (non-verbal) IQ is 122 and her verbal IQ is 101. And that is quite substantial imbalance, especially for a girl, because for girls the verbal IQ is usually higher than the performance IQ. (Actually, this is exactly as I had predicted. Yesterday evening, I told Li-Xia that the result would say that her performance IQ is 120 and her verbal IQ is 95.) She also scored positive on the dyslexy test. One can ask if this an aquired form of dyslexy due to the imbalance. Although one should always be skeptical with respect to the outcome of an intelligence test, her IQ profile is rather rare. In case of an imbalance, which is defined as a difference of more than 12 points, it is only in one out of eight cases that the non-verbal IQ is higher than the verbal IQ.

Saturday, March 12, 2005

Snow rain and curly kail

Today, I noticed some rather big snowflake falling from the sky, but when I looked outside I saw it was also raining. A strange combination rain and snow at the same time. When in the afternoon, I went into the city, it happened again: snow and rain at the same time. That is when I decided to call this "snow rain". When I was about to leave home from the city and half of the shops had closed, I decided to look in a supermarket to see it they had nay curly kail. To my surprise they did, and it was much cheaper than last year. Within five minutes, I bought all the ingredients for making curly kail hotchpotch. It was already getting close to dinner time when I came home and Li-Xia already started preparing dinner, when Annabel begged that I would make the hotchpotch. She did convinced me, and I ended up preparing the hotchpotch. This time it went much faster then last Sunday because I did not have to wash the curly kail again.

Monday, March 14, 2005

Knowing the time

When I came home, I heard that the teacher of Andy had phoned Li-Xia to ask her if she could come to catch him, because he was too ill. Andy had been a little bit ill in the past days. He had some fever and has been coughing a lot. He might also suffer from a ear infection as part of the deal. When I asked Andy when he had come home, he immediately said "Half een" (Dutch for half past twelve). And to my astonishment, that was a quite accurate answer.

Wednesday, March 16, 2005

Today, I lost the saddlebag I used for my bike. It is a cotton saddlebag that I used to take off when I went inside. I must have forgotten to tie it properly and lost it because I was in such a hurry to go to a meeting with the teacher of Annabel and someone else about the test that Annabel had with respect to her being dyslectic. I only discovered that it was lost when I arrived at the school. I biked back a little bit and tears came in to my eyes with the idea that it might be lost for good. I really like this bag, because it was simply elegant. I returned because I had to attend the meeting. At the school I phoned to my office to ask if I might have simply forgotten. That was not the case. After the meeting, I biked back to my office, but did not find it along the road. Also my hope that I might have forgotten to put it on in the bike parking near the office turned out to be idle. I am afraid that I will never find a bag like it again. The bag also contained my Vision Poncho. I will have to buy a new one.

Saturday, March 19, 2005

Weekend alone

This weekend both Annabel and Andy are away for two nights. Annabel is staying with a friend in Hengelo, and Andy went to the weekend care for the second time. (The first time was on the weekend from Friday, 18 till Sunday, 20 Februari.) Today, we took it very quiet with getting up. Around eleven we went into the city. We had thought about watching the movie "Ray" about Ray Charles. But then as the time was coming closer, we were a little doubtful. When we finally decided to go, we were a little late and missed the first ten minutes of the movie. This is the second time Li-Xia and I went to see a movie with the two of us. (The first time was on February 11, 2004 when we went to see "Lord of the Rings: The Return of the King".) We enjoyed the movie. But it is not a movie that I would have missed seeing on the big screen. I found the end of the movie a little chaotic. Afterwards we had some doner kebap (lamb meat) and falafel at Camel restaurant. We were both tired and went to bed around half past nine.

Tuesday, March 22, 2005

Pruning the willow

Today, it was a very warm day for the time of the year. During dinner, I suggested that I would start with the pruning of our willow in the back garden. It is two and half year ago that we did it for the last time. When I started, I noticed it was very easy to off most of the branches. I also just a saw for some of the thicker branches. In less than two hours I pruned the whole tree and we were able to clear most of the rubbish. We stopped when it started to rain.

Wednesday, March 30, 2005

Go club

Annabel and I went to Go club to play Go. We were the first ones to arrive. Annabel played against Marcel on a 13x13 board. They played three games. The first two (where Marcel had a nine and eight stone handicap) games she won. The last (where Marcel had a seven stone handicap) she lost, because she made some mistake. I played against Rudi. He got a nine stone handicap. In the early part of the middle game, I made a mistake, and gave away a group. Still, I only lost with about 25 points, which is not bad, if you realize that he is a 5 Dan player.

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