Computer Chess Club Archives




Subject: CCT4 notes - Arasan

Author: Jon Dart

Date: 17:08:24 01/20/02

CCT-4 notes

Here are some notes re Arasan's participation in CCT4.

I had a worry a couple of weeks ago when my wireless network quit
working. I have a couple of Linux boxes and a network hub in the
basement. But the fast machine, the Athlon, is upstairs on a wireless
link. It broke, and it would be a pain to move the Athlon downstairs
onto the wired net, so I was afraid I'd have to use a Pentium III/733
for the tournament. But I was able to get a replacement wireless card
in time and all was well, hardware-wise, anyway.

I am still tuning Arasan. In the last year or so I have made king
safety changes, extension changes, bug fixes, and built a new opening
book. Oh yeah, and ported it to Linux. None of this is publically
released yet. Soon, I hope.

Arasan was paired against Ferret (!) in the first round. Bruce reminded
me that Arasan has played several games against Ferret on ICC under
the handle "Mink", but Mink was on a lot slower hardware. Ferret had
a dual Athlon setup for the tournament. Arasan played a somewhat
passive English Opening setup. Not bad, but not very active. Ferret
crushed it.

Next round I had PolarChess. Arasan got an early advantage and won

Round 3 Arasan was matched with monsoon. Arasan has played monsoon
on ICC. It is a strong engine. I am impressed, in fact, with how
many good amateur engines there are. Chester, Insomniac, monsoon,
amyan, tao, to name just a few.

monsoon played the Benoni, which I think is just bad for Black. But
Arasan chose the Four Pawns defense (A68), which is far from the
best system. 7. Nf3 is better than f4. I think White can also play g3.
Arasan played into the f4 line because there were some draws and
wins with it from the White side in its book database. But I think
15 .. Nb6 may bust this line. After that, Arasan played one move out
of book (16. Qb3) and the next move was failing low. It doubled the
search time but still had a bad position, and it never really
recovered. Which is not to deny that monsoon played well. But I took
the f4 line out of the book since this game.

Round 5 today Arasan was matched with Tao. Arasan had the White side
of a Tarrasch defense. At least that's what I think it was. Tao gave
up a Rook for Bishop plus two pawns at move 25. A short time later it
had posted a rook on the 7th and advanced its passed pawn, with a
decisive advantage.

Round 6, Arasan played Avernox. Arasan has a reasonable record against
Averno on ICC. But here it hit another opening problem, playing the
Pirc defense. After 1. e4 d6 2. d4 Nf6 3. f3 d5 4. e5, Arasan was out
of book and soon had a miserable position. The pawn on e5 continued
to cramp it through much of the game. It was able to exchange down
and escape immediate danger but wound up down material in the endgame
and succumbed.

This showed up a problem in Arasan's book selection code. Normally it
scores each possible book move and uses a combination of move
frequency, win/loss percentage, and book learning to score each move.
But move selection is then random. It will prefer moves with high
scores, but as long as the score is not zero, the move has some
probability of being selected. So .. d6 after e4 is a possibility,
although not likely.

I now plan to implement some selectivity. I think Crafty has a similar
feature: if I set the selectivity to 70, for example, it shouldn't play
moves whose score is less than 70% of the highest move's score. This
will narrow the opening book selection but also steer it into more
main lines. I almost have this coded and it should be in place by next
week. I think randomness is good against human players but against
computers you probably want a higher selectivity value.

Round 7, Arasan played Armageddon, which is a Polish engine I've never
heard of before. Arasan dropped a pawn early in the opening and had to
play most of the game with a minus score, which was not fun to watch.
However, in the end it wound up in an endgame in which the extra pawn
was ineffective. Arasan had only 4-man tablebases and its opponent
had the full 5-man set, so it was lucky to draw here: it was depending
on search while Armageddon was getting steady tablebase hits (according
to the operator's comments during the game).

Well, it was fun, and I learned some things. So I'm looking forward to
next week.

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