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Computer chess
Evert
Member #794
November 2000
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Kirr said:

Cool! Please post any match results!

So far, I've been running a series of mini-matches against both micro-max and TSCP. The number of games is smallish, but results are fairly consistent: my program (current version, not the version I attached earlier) should be about 300-400 elo stronger than either of those two programs. However, test results are only ~150-200 elo stronger. There appear to be two problems.

One is with picking the fastest mate. The program should always pick the fastest mate (so it prefers a mate-in-two to a mate-in-three), but sometimes this doesn't seem to work properly. I suspect a problem with the transposition table, where the score for a position that was previously scored as "mate-in-N" has been lost, but the program finds the previous position, which was scored as a "mate-in-N+1" and decides that it will win from that position - and go back. Again, there's code in place that should prevent that, which usually works... something to look into, evidently.
The other is with three-fold repeat detection: the program sometimes goes into a repetition, even if it's ahead and it will get a draw instead of a win. This is where it loses most of its score in the test matches. I again suspect the transposition table: the code looks at the current position, checks if it's a repetition, if not it looks in the transposition table and then blindly executes that move and returns the score - without checking if that leads to a repetition.

Some interesting things I found:

  1. In one of the test games (I'll have to look it up) my program was playing a rook ending (one rook each) with a free pawn and it correctly went for the Lucena position, building a bridge with its rook on the fifth rank. What's cool about this is that it doesn't know about rook endings at all, which means that it found the win through the normal search.

  2. My program will score two connected pawns on the sixt row as stronger than a rook. I may need to temper this a bit depending on the opponent's material because I have the impression it sacrifices material a little bit too readily to reach this situation. It can be a real killer in some situations though, where it's fun to see!

  3. My program seems to end up a lot with the situation where it has knights against bishops. I like to think it "plays well" with knights as a result, but I suspect something else entirely is going on: following Kaufman's analysis of material imbalances I award a bonus for knights in positions with a lot of pawns. The result is probably that my program prefers knights to bishops early on in the game and will more readily exchange one or both of its own bishops for knights (especially if it can also win a pawn or break up the enemy bishop pair). This isn't that great in the end game, however...

So, work to do, apart from isolating those bugs (which will be annoying, because they only seem to show up in the test matches so far). I'll probably also replace Kaufman's evaluation stuff by something else. I already took out his rook evaluation things (rooks are worth more in positions with fewer pawns) because that condition didn't make any sense to me and gave some funny results. Rooks are worth more on open or semi-open files, where they have greater mobility - which usually happens later in the game when there are fewer pawns on the board. The fact that there are fewer pawns by itself doesn't make rooks more powerful. It should be similar for knights: they're not as strong in the end game if there are pawns on both wings.

Damn! My program just dominated micro-max' queen with three minors (knight and bishop pair) and then slipped into a threefold repetition again!

Quote:

If you make a simple web-page with short description and download link, you can announce the engine and enter tournaments. :)

Working on it. :)
I also have to iron out some details for the UCI protocol. Right now, I can only change the time settings by hand in the code, so I have to make sure that what the UI thinks the time controls are matches what my program thinks they are - or it would be unfair. :)

Kirr
Member #5,060
September 2004
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Evert said:

So far, I've been running a series of mini-matches against both micro-max and TSCP. The number of games is smallish, but results are fairly consistent: my program (current version, not the version I attached earlier) should be about 300-400 elo stronger than either of those two programs. However, test results are only ~150-200 elo stronger.

Great results for such a short development time! It looks like your program is about 2100 or 2200 points on KCEC or CCRL scale. If you like to test against stronger programs, just pick any entry with similar rating from the lists. For example, I would try Gk 0.90 64-bit.

Evert said:

There appear to be two problems.

One is with picking the fastest mate. The program should always pick the fastest mate (so it prefers a mate-in-two to a mate-in-three), but sometimes this doesn't seem to work properly. I suspect a problem with the transposition table, where the score for a position that was previously scored as "mate-in-N" has been lost, but the program finds the previous position, which was scored as a "mate-in-N+1" and decides that it will win from that position - and go back. Again, there's code in place that should prevent that, which usually works... something to look into, evidently.

It's a common problem. I know a number of engines that have troubles checkmating, including some rather strong ones (e.g., Smarthink 0.17a). In extreme cases they fail to win a KQQK endgame, which ends by 50 moves rule. I think it's not a too much serious problem, though of course it's best to fix it.

Evert said:

The other is with three-fold repeat detection: the program sometimes goes into a repetition, even if it's ahead and it will get a draw instead of a win. This is where it loses most of its score in the test matches. I again suspect the transposition table: the code looks at the current position, checks if it's a repetition, if not it looks in the transposition table and then blindly executes that move and returns the score - without checking if that leads to a repetition.

This is more serious - it may cost your engine many points, especially against weaker engines.

Evert said:

Some interesting things I found:

1. In one of the test games (I'll have to look it up) my program was playing a rook ending (one rook each) with a free pawn and it correctly went for the Lucena position [en.wikipedia.org], building a bridge with its rook on the fifth rank. What's cool about this is that it doesn't know about rook endings at all, which means that it found the win through the normal search.

Interesting.. By the way, are you planning to employ any endgame tablebases?

Evert said:

My program will score two connected pawns on the sixt row as stronger than a rook. I may need to temper this a bit depending on the opponent's material because I have the impression it sacrifices material a little bit too readily to reach this situation. It can be a real killer in some situations though, where it's fun to see!

Yes a pawns race is often fun to watch!

Evert said:

My program seems to end up a lot with the situation where it has knights against bishops. I like to think it "plays well" with knights as a result, but I suspect something else entirely is going on: following Kaufman's analysis of material imbalances [home.comcast.net] I award a bonus for knights in positions with a lot of pawns. The result is probably that my program prefers knights to bishops early on in the game and will more readily exchange one or both of its own bishops for knights (especially if it can also win a pawn or break up the enemy bishop pair). This isn't that great in the end game, however...

Yes, bishops are usually preferable in the endgame. (Except when you have an 'a' or 'h' pawn and a wrong color bishop, do you detect this?) Are you detecting game phases? People often adjust bonuses depending on game phase.

Evert said:

Damn! My program just dominated micro-max' queen with three minors (knight and bishop pair) and then slipped into a threefold repetition again!

:)

Evert said:

I also have to iron out some details for the UCI protocol. Right now, I can only change the time settings by hand in the code, so I have to make sure that what the UI thinks the time controls are matches what my program thinks they are - or it would be unfair.

Yes, support for changing time control is very important, or with wrong clock your program will either move too fast or lose on time. By the way it's also good if you'll test your program with very fast time control, like 1 min/game. Time losses are very annoying, and often happen in my tournament.

Did you already choose a name for your engine? :)

--
"Go to the NW of Stonemarket Plaza to the Blue Glyph Keeper Library door and enter."
- Lunabean's Thief Deadly Shadows Walkthrough, day eight

Evert
Member #794
November 2000
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Kirr said:

Great results for such a short development time! It looks like your program is about 2100 or 2200 points on KCEC or CCRL scale. If you like to test against stronger programs, just pick any entry with similar rating from the lists.

I'll do that - once I get these bugs fixed... :(
Remember, it's not my first try at a chess program.

Quote:

It's a common problem. I know a number of engines that have troubles checkmating, including some rather strong ones (e.g., Smarthink 0.17a). In extreme cases they fail to win a KQQK endgame, which ends by 50 moves rule. I think it's not a too much serious problem, though of course it's best to fix it.

Preferring a distant mate over a quick mate is a problem I've wrestled with in the past, but this is very different and confusing. Right now, I seem to have "fixed" the situation by clearing the transposition table if the current position is a repetition and scored as a mate. I could do a mate verification search, but that could be very costly if the mate is very deep.

Quote:

This is more serious - it may cost your engine many points, especially against weaker engines.

Yes. It's a rather nasty problem though: it doesn't show up anymore when I run it through its own GUI, so the bug has something to do with the way the UCI protocol interacts with the way the engine works internally.
By now I've fixed half a dozen things that could have caused that problem and it's still there. The repetition table seems to be updated correctly now, so the problem is elsewhere...

EDIT: fixed it! At least, the engine now properly wins a game where it entered a pointless repetition before. It was quite nasty: there was a bug in the UCI protocol code (the repetition table wasn't reset) which I fixed, but in the mean time I'd changed the logic in the search code in an attempt to fix the problem - but that code had a bug too and produced the same problem on its own. Argh!
I also fixed a nasty bug where an en-passant capture would not be recognised as a valid out-of-check move.
By now, my program has solved every single test position in the "Win at Chess" test set in under 10s at some point or another, but never all of them at once! Improve something so position X is solved in 10s and now position Y is not found. Overall, the trend has been to better test results though (currently 290/300) so I can't complain too much.

Quote:

Interesting.. By the way, are you planning to employ any endgame tablebases?

Not yet. I might at some point, if they're worth it. My understanding is that they don't actually add that much in terms of playing strength (although it does help, obviously). KRKRP might be interesting though.

Quote:

Except when you have an 'a' or 'h' pawn and a wrong color bishop, do you detect this?

Not yet; the situation arises quite often (although my program usually isn't the one with the bishop) so I probably should put it in. I'm not sure at what point to include it though: obviously if it's king+bishop+wrong rook pawn against a lone king and obviously not when there are still rooks or too many other pawns in play. I'd like to score such positions as draw-ish though, so the program knows its position is not as good as raw material would suggest.
Which reminds me: it should score lone kings or king+minor vs. lone king as draws too.

Quote:

Are you detecting game phases? People often adjust bonuses depending on game phase.

Sortof. I have some detection for the opening and the middle game and then there are some terms that become more important when there is fewer material on the board and some bonuses that are only given when there are only pawns left.
It's apparently important to make sure that the evaluation function changes relatively smoothly, and having a hard cut at some point could hurt the way the program plays. I know others use some sort of interpolation between a middle-game and an end-game evaluation function.

Quote:

Yes, support for changing time control is very important, or with wrong clock your program will either move too fast or lose on time. By the way it's also good if you'll test your program with very fast time control, like 1 min/game. Time losses are very annoying, and often happen in my tournament.

Will do. I have a basic framework in place for doing time management. It still only does a fixed time per move at the moment, but I'm working on it.

Quote:

Did you already choose a name for your engine? :)

It's called "Jazz" at the moment. My previous attempt was called "Isildur", which I also still like as a name (in which case this would be Isildur 2.0). Or I might combine the two into "Islidur Jazz". Or think of something else entirely.
:)
For now, Jazz will do.

I'll try to manage another code upload next weekend (as well as a more Linux-friendly version; I have no idea if things would compile on Windows though).

Thomas Fjellstrom
Member #476
June 2000
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For names try: Anarion, Aratan, Ciryon, Elendur, or Valandil (being sons, or the younger brother of Isildur).

--
Thomas Fjellstrom - [website] - [email] - [Allegro Wiki] - [Allegro TODO]
"If you can't think of a better solution, don't try to make a better solution." -- weapon_S
"The less evidence we have for what we believe is certain, the more violently we defend beliefs against those who don't agree" -- https://twitter.com/neiltyson/status/592870205409353730

Evert
Member #794
November 2000
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Hmm... those are neat too! I could write a series of chess programs that descend down the line of Tolkien's house of Elendil. It'd take me a while to get to Aragorn. :D

Anyway, latest test results are in: my program scores 90% against micro-Max. It needs two or three things to score 100%, I think: a better notion of king safety (it left the king vulnerable to attacks in two games, one lost and one drawn as a result), a better evaluation of material imbalances (two pawns for a minor is not a good deal if the opponent still has many pieces, even if you have three connected free pawns) and it needs to push free pawns a little more aggressively. And I need to make the program not end up with knights in the end game, because it just makes it more difficult to win (one game drawn because of that).

Thomas Fjellstrom
Member #476
June 2000
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Evert said:

Hmm... those are neat too! I could write a series of chess programs that descend down the line of Tolkien's house of Elendil. It'd take me a while to get to Aragorn. :D

Do as apple does, and name each new version something different :)

--
Thomas Fjellstrom - [website] - [email] - [Allegro Wiki] - [Allegro TODO]
"If you can't think of a better solution, don't try to make a better solution." -- weapon_S
"The less evidence we have for what we believe is certain, the more violently we defend beliefs against those who don't agree" -- https://twitter.com/neiltyson/status/592870205409353730

Matthew Leverton
Supreme Loser
January 1999
avatar

Jazz is a much better name because it can actually be pronounced by somebody other than a Tolkien nerd.

I'd comment on the game itself, but it won't compile on MSVC without a major facelift and regardless, as I don't have the patience to play chess, I am horrible at it.

Evert
Member #794
November 2000
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Jazz is a much better name because it can actually be pronounced by somebody other than a Tolkien nerd.

It also vaguely sounds like "Chess" - which now reminds me that another member of my old chess club once called his chess program "Jas", the Dutch word for "coat" which has a similar pronunciation to "jazz". That association must have stuck!

Quote:

I'd comment on the game itself, but it won't compile on MSVC without a major facelift

I'm not surprised.
It might be worthwhile to do at some point, especially since MinGW doesn't do 64 bit binaries as I recall. On the other hand, I don't know how wide-spread 64 bit Windows is these days...

Quote:

as I don't have the patience to play chess, I am horrible at it.

;D
There are engines out there that play variations like suicide chess or atomic chess. You might have more fun with those.

Anyway, I've upgraded my setup to play matches against gnuchess. As I suspected, I need to do a better job at king safety and material imbalances. Some end game knowledge wouldn't hurt either. It scores about 30%, which is consistent (rating-wise) to scoring 90% against micro-max.

Alianix
Member #10,518
December 2008
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Hey Evert, I hear you have some working source to compile, where is it ?

ReyBrujo
Moderator
January 2001
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Attached here, but he may have uploaded a newer one later.

--
RB
光子「あたしただ…奪う側に回ろうと思っただけよ」
Mitsuko's last words, Battle Royale

Evert
Member #794
November 2000
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Nope, that's the latest uploaded source. I should post the updated source soonish too.

Alianix
Member #10,518
December 2008
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It gave me this after hacking your Makefile:

obj//a5jazz.o: In function `spawn_async_file_dialog':
a5jazz.c:(.text+0x9a9): undefined reference to `al_create_user_event_source'

...I guess I need an earlier version of a5 ? I have 4.9.13 now only. :-/

Evert
Member #794
November 2000
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No, you probably need a more recent version (ie, svn). It's a bit odd, since I though I had everything set up so it would compile with either version, but maybe not. I didn't test that very extensively since I didn't feel like reinstalling 4.9.13 after I updated.

If this is Linux, you'll want to add qsort.o to the list of object files, or you'll miss the qsort_r() function.
Yes, I should automate that by using a better build system than a static Makefile. ;) It's on my (long) list...

Matthew Leverton
Supreme Loser
January 1999
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al_create_user_event_source() has recently been replaced with al_init_user_event_source().

Evert
Member #794
November 2000
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It should pick up al_create_user_event_source() if you're using 4.9.13:

#if ALLEGRO_WIP_VERSION < 14
   data->event_source = al_create_user_event_source();
#else
   al_init_user_event_source(&data->event_source);
#endif

Alianix
Member #10,518
December 2008
avatar

Now I'm getting these...after installing SVN

a5jazz.c:(.text+0x265e): undefined reference to `al_get_mouse'
a5jazz.c:(.text+0x2670): undefined reference to `al_get_keyboard'
collect2: ld returned 1 exit status
make: *** [a5jazz] Error 1

also why do you have -g with -O3 ?
and OBJDIR=obj/ should be OBJDIR=obj maybe ?

Evert
Member #794
November 2000
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Alianix said:

Now I'm getting these...after installing SVN

Ah, right. Yes. Ok, those were removed after I uploaded the above source. Check the README file, it should list the exact revision number that I used at the time.

Quote:

also why do you have -g with -O3 ?

So I get function and variable names in gdb when something causes a segfault or accesses out-of-bounds memory.
It's perfectly fine to use -g in combination with optimisations.

Quote:

and OBJDIR=obj/ should be OBJDIR=obj maybe ?

Doesn't matter one way or the other.

Alianix
Member #10,518
December 2008
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Ok I understand, bummer, I have a fresher revision... ;D

The whole thing is pretty funny, gotta love WIP... no compromise...

I think I'll try to fix the source, if it does not take more then 5 min...otherwise i'll wait for the mercy of the creator ;D

Edit:
...gave up and bailed out ;D

Evert
Member #794
November 2000
avatar

It's a good point, actually: I didn't update my installed version of Allegro yet either, I should do that before I upload the new source for my chess program (although strictly speaking you don't need Allegro in order to use it...)

Alianix
Member #10,518
December 2008
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Ye i gather that, i tried the test progs and it worked fine, in the meanwhile i fixed the source too so it compiled, i'm trying it now...

The chessboard is flickering a lot, is that normal ?

Edit:

Ok besides the maddening flickering it seems to be working right, I'll try to fix that later...But it looks and seems very nice so far, I'll be playing with it...Thanks Evert !

Thomas Fjellstrom
Member #476
June 2000
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Evert said:

It's perfectly fine to use -g in combination with optimisations.

Only if a person understands that the code will be changed quite a bit, so you shouldn't expect to have a 1:1 relationship from the path gdb takes, and what you have written in your source.

I'm sure Evert does though :)

--
Thomas Fjellstrom - [website] - [email] - [Allegro Wiki] - [Allegro TODO]
"If you can't think of a better solution, don't try to make a better solution." -- weapon_S
"The less evidence we have for what we believe is certain, the more violently we defend beliefs against those who don't agree" -- https://twitter.com/neiltyson/status/592870205409353730

Evert
Member #794
November 2000
avatar

Alianix said:

The chessboard is flickering a lot, is that normal ?

It doesn't on my machine... but it might be, depending on your system setup. I'm told I should process expose events, which the version I posted here doesn't do but the current version supposedly does. I say supposedly, since expose events are never generated on OS X, so I haven't been able to test.
That's assuming that that is indeed the problem...

Quote:

Ok besides the maddening flickering it seems to be working right, I'll try to fix that later...But it looks and seems very nice so far, I'll be playing with it...Thanks Evert !

He, wait until I find time to clean up and upload the current version! It's considerably stronger than the old one (it's about on-par with gnuchess, according to a few mini-matches I did a few days ago and allowing for a slight increase in playing strength since then).

I'm sure Evert does though

Yup. ;)
It usually spits out something vaguely sensible. If not, I can probably find the last time I touched a pointer/array and figure the problem out from there, since that's probably when I broke things if the error wasn't there before.
Using svn (or cvs) is also a great for debugging (if you introduced any new bugs that is).

Remember the problem I mentioned above where the program was going into repetitions if it found a mate-score in the transposition table? I was browsing through Crafty's revision history when I found this:

Quote:

  • 8.13 NextCapture() now always tries checking moves if the move at *

* the previous ply was a null-move. This avoids letting the null *
* move hide some serious mating threats. A minor bug where Crafty * * could draw by repetition after announcing a mate. This was a * * result of finding a mate score in hash table, and, after the * * search iteration completed, the mate score would terminate the * * search completely. Now, the search won't terminate until it *
* finds a mate shorter than the previous search did. Minor eval *
* tweaks and bugfixes as well. *

Glad I'm not the only one who runs into problems like this! ;D

ReyBrujo
Moderator
January 2001
avatar

Even if you don't want to polish ending game right now, you could go to chessproblems.com and see if your program is able to find the asked mates.

--
RB
光子「あたしただ…奪う側に回ろうと思っただけよ」
Mitsuko's last words, Battle Royale

Kirr
Member #5,060
September 2004
avatar

Both "Isildur" and "Jazz" are great names, however not the combination of the two. :)

Evert, will it be possible to compile your engine without allegro? Or, at least, will there be an option to just run it in text mode without any graphics?

Evert said:

It's considerably stronger than the old one (it's about on-par with gnuchess, according to a few mini-matches I did a few days ago and allowing for a slight increase in playing strength since then).

Interesting, because from last week GNU Chess also started to play in my tourney. Currently #78 in my list with rating of 2344 points, after 160 games. However it's so buggy that it's not a good engine to use as a rating reference. (It has serious time management problem when playing with external book, which makes it about 100 points weaker, alternatively it can play without any book to become only about 50 points weaker, these are initial rough estimates, more accurate estimates in September. Details here).

EDIT:

Evert said:
Kirr said:

Interesting.. By the way, are you planning to employ any endgame tablebases?

Not yet. I might at some point, if they're worth it. My understanding is that they don't actually add that much in terms of playing strength (although it does help, obviously). KRKRP might be interesting though.

Practical benefit from Nalimov (or other DTM/DTC/DTZ) tables is very small, but some bitbases should give measurable strength increase, since bitbases are must smaller and faster to access (so you can probe them deeper in search), so you can keep much of them in RAM. Daniel Shawul's Scorpio bitbases is one nice open source impementation, used by number of other engines. (link)

--
"Go to the NW of Stonemarket Plaza to the Blue Glyph Keeper Library door and enter."
- Lunabean's Thief Deadly Shadows Walkthrough, day eight

Evert
Member #794
November 2000
avatar

ReyBrujo said:

Even if you don't want to polish ending game right now, you could go to chessproblems.com and see if your program is able to find the asked mates.

I'll have a look. Most mate problems tend to be relatively easy though, since they're usually sequences of forced moves. Note that that just means finding "a mate", not necessarily the best one!

This little beauty

gets solved in about 0.2s:

Quote:

[10] +999.88 0.20 17019 (<BR>=4.71, EBR=0.57) 9 / 0 Rh5 Bh7 Bxf6
Mate in 7 (12 ply)
--> Rh5 999.88
Rh5 Bh7 Bxf6 Kg6 Rg5 Kh6 Kxf7 Bg6 Rxg6 Kh7 Rg8 Kh6 Rh8
17019 nodes visited (15393 [47.49%] in transposition table), 159321 nodes/s

However, the "correct" answer is 1. Rh6!, which is a mate in 5 (a mate in 5 starting with a rook sacrifice and followed by three quiet moves; not very nice for a computer).
They're good positions to check whether code to detect threats works, however.

In practice it doesn't really matter of course if you find a mate-in-N or a mate-in-N+a-bit, as long as you actually deliver the mate!

Kirr said:

Evert, will it be possible to compile your engine without allegro? Or, at least, will there be an option to just run it in text mode without any graphics?

Oh yes. The engine itself is just a few interface functions that manipulate a "game" or "board" object (one is everything to do with the current game, one is about the current position only). The interface (any interface) is deliberately decoupled from that.
Right now I have about 5 different "interfaces": the Allegro-based one, a console one I never really did anything with after making the Allegro-based one (I use it to solve individual test positions though), a "perftest" that counts the number of nodes from the starting position after a certain fixed depth and measures the time it takes to get there (useful for debugging the move generator, apparently, though it hasn't helped me there, I've mainly used it to measure the effect of optimisations on the move generator and make-move functions), a "test" driver that loads a collection of test positions and runs them through the engine for a given time-per-move and the UCI interface (to the extent that this currently supports the full UCI protocol). Only the Allegro-based interface depends on Allegro.

Quote:

Interesting, because from last week GNU Chess also started to play in my tourney. Currently #78 in my list with rating of 2344 points, after 160 games.

Sounds about right, comparing the relative strengths I've seen in other rating lists.

Quote:

However it's so buggy that it's not a good engine to use as a rating reference. (It has serious time management problem when playing with external book, which makes it about 100 points weaker, alternatively it can play without any book to become only about 50 points weaker,

Hmm... ok, I'll bear that in mind. My code still doesn't have an opening book (although it doesn't bodge things up as badly as it used to anymore) but since it's a UCI engine, I've taken the cheap way out and let the interface handle the opening for now (since I'm playing it against xboard engines under xboard, that means I'm running it through polyglot).

Quote:

Practical benefit from Nalimov (or other DTM/DTC/DTZ) tables is very small, but some bitbases should give measurable strength increase, since bitbases are must smaller and faster to access (so you can probe them deeper in search), so you can keep much of them in RAM. Daniel Shawul's Scorpio bitbases is one nice open source impementation, used by number of other engines.

Thanks! I'll have a look. My understanding of bitbases is that they only offer information on whether a position is "won", "lost" or "draw". While I'm sure that's useful information, I need to work out how to implement that in the alpha-beta framework of a chess engine, where I'd typically want to know more than simply "won"; for instance, won in how many moves.
On the other hand, the main advantage is probably that you get an accurate evaluation of the position in a leave node near the search horizon after exchanging into the end game, where you otherwise wouldn't be able to tell as accurately whether it's a good ending or not and so whether you should exchange into it or not.

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