The 1st release of both engines is done

Today I published both engines (mACE and iCE) to my homepage, so whoever wants to give them I try can now do so.

I also started a little tutorial about chess programming there, so who is interested might have a look at
http://www.fam-petzke.de/chess_home_en.shtml.

About to release the 1st public version

After the last tournament where the ice engine did not so bad, I decided to take a little rest from the core engine programming. I plan to make the engine available for download via my private web site and have to do some preparation for that first. I will post the first public release of my engine as soon as this is finished.

Stay tuned !

Small private tournament

I felt it is time to match the engine against some other engines to see how it performs and also to have a baseline to measure progress over time. I ran a small tournament of 6 engines. I took some of the free engines available on the net and tried to avoid ones known to be very strong. There is no point in proofing that ice is still a weak engine.

The engines I selected were BB Chess, Delphil2_6, Kanguruh93, Mediocre and Vicki.

Ice finished 3rd place scoring 9,5 points in 15 games. Seems that ice plays somewhere in the range of those engines and is not a total looser anymore. I'm a little proud and feel the days come closer where I'm able to make it available for download.

Here are the tournament details

Arena tournament

Rank	Engine	Score	De	Me	Ic	BB	Vi	Ka	S-B
1	Delphil2_6a	12,0/15	· ··	110	100	111	111	111	69,50
2	Mediocre	10,5/15	001	· ··	11=	001	111	111	57,75
3	Ice Latest	9,5/15	011	00=	· ··	101	==1	111	55,25
4	BBChess0_99b	8,5/15	000	110	010	· ··	1=1	111	41,75
5	Vicki	4,5/15	000	000	==0	0=0	· ··	111	13,75
6	Kanguruh93	0,0/15	000	000	000	000	000	· ··	0,00

45 games played / Tournament is finished

 Tournament start: 2011.03.05, 23:56:04
Latest update: 2011.03.06, 10:20:49
Site/ Country: Germany
Level: Tournament 40/5
Hardware: Intel(R) Core(TM)2 Duo CPU P8600 @ 2.40GHzDual 2394 MHz with 1.992 MB Memory
Operating system: Microsoft Windows XP Professional Service Pack 3 (Build 2600)
Table created with: Arena 2.0.1

Another bug hunting session

As mentioned in an earlier post I develop the ice engine with MSVC and compile the release versions with the gnu c++ compiler as it creates the faster executable. At some point in time I realized that both executables compiled from the same source produced different outcomes.

When searching for a move suddenly the number of processed nodes was different, different pvs were calculated and sometimes also different best moves were returned. So I knew there was a bug some where but it was very hard to spot as both programs just for themselves appeared to run fine.

I reversed recent code changes to spot the source of the error but it did not help, both versions behaved differently, so I started the bug hunting session. Errors produced by the search algorithm are very hard to spot because the algorithm is recursive and calls itself several thousand times a second. I finally was able to spot the last position were both programs were equal, so I knew this position was somehow the cause of the problem. It showed that eval returned in both executables different scores for that position. From now on it was easy as eval is not recursive.

The root cause was an array with pawn bonuses per rank. The array was sized too small. In some positions the access to that array just exceeded the bounds of the array and retrieved a random number that just happened to be at the memory position. This random number was not the same in the MSVC and the gnu version and so the execution started to run differently.

This was then a quick fix and now both versions are consistent again.

I ran a quick tournament (50 games) of the latest ice version against a former not too old release to measure whether recent changes improved the strength of the engine. And the latest release scored

38 : 12

So although I consider the engine rather weak at least there seems to be some progress.

Chess engine input handling

When designing the ice engine I decided to design it as a single threaded program to save the thread handling overhead.

In the pascal mace engine I use threads for the input handling. I read from stdin, when no input is available the execution stops. This is unfortunate if this is your main thread, it is no problem when it is an extra thread created just for that purpose. In ice I wanted to use PEEK_NAMED_PIPE to look whether input is available and only start reading if it signals that input is there, so the execution is not blocked by reading from an empty input device.

It worked most of the time, it failed when I gave the console window, where the engine is running in, focus or removed focus. Although I specified that I don't want to have window events PEEK_NAMED_PIPE returned true in those cases, it tried then to read from stdin and execution stopped as no real input was available.

This only happens when I run the engine in a console window not when the engine is running as a process started by the GUI (try to give focus to a process ...) but it is annoying anyway.

I returned to the thread method for handling stdin input. I use the standard methods from Windows to do that and the performance hit I'm taking seems minimal.

Next to last mistake

Victory goes to the player who makes the next-to-last mistake.
Savielly Grigorievitch Tartakower, Chess Master

While working on the engine evaluation I thought it might be helpful for me to play some games against other real players to get some fresh ideas. It's been a while since I did that.

I went to yahoo chess and played a few games. As a noob I was given a low provisional score and engaged games with players that had a comparable score. To my surprise there were players with a low score like me that played already thousands sometimes more than ten thousands games. I don't think I played ten thousand games in my whole life and if I had I would probably have a better score.

Anyway the last game was a real challenge for me. My opponent played very aggressive and I was somehow intimidated by that. I thought I was screwed but I just wasn't able to find the best moves. I performed an analysis of the game after wards with the help of my engine and it showed that we both played terrible. His gambit offers were incorrect so was my declining, I overlooked easy tactical combination's.

Here is the game (I'm playing White)

1.  e2-e4 e7-e5
2.  g1-f3 b8-c6
3.  f1-c4 g8-f6
4.  d2-d3 f8-c5
5.  o-o   f6-g4
6.  d1-e2 d7-d6
7.  h2-h3 h7-h5

I thought it is too dangerous to accept the gambit and take the knight, because of the open h-file with blacks rook on it. But after 9. Ng5 it would probably be ok to take it. Instead
 

8.  b1-c3 c8-e6
9.  c3-d5 c6-d4
10. e2-d2 d4xf3+
11. g2xf3 d8-h4
12. d2-g5 

Black is too greedy

12. ... h4xh3
13. g5-e7++

At the end he was so occupied with his assault that he overlooked the Mate in 1 threat and this one time I was aware of it, so I won luckily. But I take this a s a warning, I need more discipline. Calculate better and consider all alternatives. Play a bit like my engine plays.

 

  

Evaluation evaluation

Last time I thought about the evaluation part of the engine. This part is responsible for returning an absolute score for a certain position. Here all the chess specific knowledge is contained. The engine must be able to see whether a certain position is in favor for white or black, so it knows which position it should avoid and which positions it should play towards to.

Easy evaluation terms are material based. The side with more material has an advantage. The bigger the material difference the higher the advantage. But even material becomes difficult when you try to fine tune that.

Example question: What is better, a queen or two rooks ?

The answer depends on the other material on the board, if there are a lot of pawns on the board, the queen might be superior because the rook paths are blocked. If there are only a few paws on the board the rooks gain a lot of strength.

A queen that is not opposed by a bishop pair is stronger than one were the opponent still possess the bishop pair.

So to tune the evaluation is probably the must difficult part and also the part the engine gets its personality from. What focus I give on certain terms will determine the engine play, so it is quite an interesting subject.

For the programming I maintain a header file with all the evaluation terms and scores associated. This is very time consuming to maintain especially if you want to have a nice code formatting.

I started to maintain the evaluation terms in a Excel and wrote a Visual Basic macro that exports the terms into c++ code. This is really helpful.

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