First fail high drops in endgame

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Tony

First fail high drops in endgame

Post by Tony » Mon May 28, 2007 7:49 pm

Hi all,

I think I broke something in my engine, but I'm not sure what. Maybe someone has a clue.

When I go towards the endgame, the percentage first fail high drops to below 80% ( normally above 90%)

I'm not sure how to test/ where to look. I switched off bitbases (thought they were corrupt), switched off lazy eval. No improvement.

anybody had this before ?

Cheers,

Tony

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hgm
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Re: First fail high drops in endgame

Post by hgm » Mon May 28, 2007 8:45 pm

Did you ever measure this quantity before (with different result)? It seems normal to me that it is more difficult to find cut-moves in an end-game, as the information that distinguishes the winning from the losing moves is much more distant. In the middle game it is often decided by what is on the to-square, but in end-games it is what is on the square you are heading to in a number of moves.

Tony

Re: First fail high drops in endgame

Post by Tony » Mon May 28, 2007 8:56 pm

hgm wrote:Did you ever measure this quantity before (with different result)? It seems normal to me that it is more difficult to find cut-moves in an end-game, as the information that distinguishes the winning from the losing moves is much more distant. In the middle game it is often decided by what is on the to-square, but in end-games it is what is on the square you are heading to in a number of moves.
Yes,
otoh, in the endgame, you accidently choose the right (good enough) move more often.

But in fine 70 , 78% is way too low. that should be 98% or something. (No nullmove, no lmr)
I've never seen it that low. It almost looks like a random choice. I'm overlooking something obvious, but I haven't got a clue.

Tony

Gerd Isenberg
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Re: First fail high drops in endgame

Post by Gerd Isenberg » Mon May 28, 2007 9:41 pm

Tony wrote:Hi all,

I think I broke something in my engine, but I'm not sure what. Maybe someone has a clue.

When I go towards the endgame, the percentage first fail high drops to below 80% ( normally above 90%)

I'm not sure how to test/ where to look. I switched off bitbases (thought they were corrupt), switched off lazy eval. No improvement.

anybody had this before ?

Cheers,

Tony
You may count fail high % for depth left > N, > 0, <= 0 to eventually get a better picture of what happens. If you cut late, log the moves tried before.

Gerd

Tony

Re: First fail high drops in endgame

Post by Tony » Mon May 28, 2007 9:53 pm

Gerd Isenberg wrote:
Tony wrote:Hi all,

I think I broke something in my engine, but I'm not sure what. Maybe someone has a clue.

When I go towards the endgame, the percentage first fail high drops to below 80% ( normally above 90%)

I'm not sure how to test/ where to look. I switched off bitbases (thought they were corrupt), switched off lazy eval. No improvement.

anybody had this before ?

Cheers,

Tony
You may count fail high % for depth left > N, > 0, <= 0 to eventually get a better picture of what happens. If you cut late, log the moves tried before.

Gerd
Hi Gerd,

problem is that the first 8 plies still give a decent percentage. So logging kind of blows up. I don't seem to be able to find a specific position that goes wrong immediatly.

I'll try with splitting the counters, that might give some more information.

Thanks,

Tony

Gerd Isenberg
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Location: Hattingen, Germany

Re: First fail high drops in endgame

Post by Gerd Isenberg » Mon May 28, 2007 10:35 pm

The professional approach would be to get your older sources from CVS or similar repositories to find the changes that cause the damage ;-)

Good luck,
Gerd

Tony

Re: First fail high drops in endgame

Post by Tony » Tue May 29, 2007 7:08 am

Gerd Isenberg wrote:The professional approach would be to get your older sources from CVS or similar repositories to find the changes that cause the damage ;-)

Good luck,
Gerd
Unfortunately, that would be about my complete source code :(

I made quite a few really big changes.

Tony

Chan Rasjid
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Location: Singapore

Re: First fail high drops in endgame

Post by Chan Rasjid » Tue May 29, 2007 8:28 am

Hello,
I think I broke something in my engine, but I'm not sure what. Maybe someone has a clue.

When I go towards the endgame, the percentage first fail high drops to below 80% ( normally above 90%)
For me, the cause of most bugs seems to be traceable to a "direct" source. In your case it may be hashing a wrong move, failure to order / retrieve the proper moves front. Is there any related endgame specific routines? Is your printf % corrupted?

Best Regards,
Rasjid
Don't believe when you're told "There's no free lunch!" There is Linux.

Jose Carlos
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Location: Murcia (Spain)

Re: First fail high drops in endgame

Post by Jose Carlos » Tue May 29, 2007 9:06 am

Tony wrote:
hgm wrote:Did you ever measure this quantity before (with different result)? It seems normal to me that it is more difficult to find cut-moves in an end-game, as the information that distinguishes the winning from the losing moves is much more distant. In the middle game it is often decided by what is on the to-square, but in end-games it is what is on the square you are heading to in a number of moves.
Yes,
otoh, in the endgame, you accidently choose the right (good enough) move more often.

But in fine 70 , 78% is way too low. that should be 98% or something. (No nullmove, no lmr)
I've never seen it that low. It almost looks like a random choice. I'm overlooking something obvious, but I haven't got a clue.

Tony
I think that's normal behaviour due to hashing. If you prune much more due to hashing (like in Fine 70), you have less good-and-easy moves to search that would otherwise rise the FH at fist move rate.
__________________________
José Carlos Martínez Galán

Tony

Re: First fail high drops in endgame

Post by Tony » Tue May 29, 2007 11:13 am

I seem to have found it.

I have created a function that converts the hashtable score to a search score (basicly adjusting for checkmates)

Unfortunately, I didn't send in the found hashtablescore, but a value initialised to +/- inf (depending on upper or lower bound), meaning it would get a hashtable cutoff with a checkmate score, any time the depth was sufficient (but never when in PV).

That will wreck your search. The only thing I don't understand is that it was able to play something resembling chess at all.

Thanks all,

Tony

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