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Dann Corbit

Joined: 08 Mar 2006
Posts: 8282
Location: Redmond, WA USA

Post subject: Re: Move ordering    Posted: Fri Nov 10, 2017 1:28 am

[quote="Sven"]
ZirconiumX wrote:
jwes wrote:
Deferring captures of lower-valued pieces was a loss of about 25 elo +/- 37:

 Code: Score of New vs Old: 84 - 103 - 63  [0.462] 250

Deferring captures of defended squares was a loss of about 50 elo +/- 37:

 Code: Score of New vs Old: 73 - 108 - 69  [0.430] 250

The two together is a small gain of 10 elo +/- 24:

 Code: Score of New vs Old: 230 - 213 - 138  [0.515] 581

None of these results is surprising (Except that I hope that you play at least 1000 games per test run next time to increase significance ...)

Capturing lower-valued pieces includes capturing undefended pieces so deferring these is suboptimal. Capturing defended pieces in general also includes moves like PxQ where the queen is defended by a piece lower than a queen, so this is even more suboptimal. Even the combination of both is insufficient since the defender could be a queen (for instance) and you might have a second attacker of the target piece so that you could capture the queen afterwards, which does not classify the first capture as a losing capture.

 ZirconiumX wrote: [...] I haven't found the combination just yet.

There is no perfect combination but if you have not implemented SEE yet and still want to decide whether a capture most probably is a losing capture then you need a combination of criteria like this:
a) higher piece takes lower piece (viewing bishop and knight as equal), and
b) captured piece is defended, and
c) the least-valued defender has a value that is low enough to be sure that you would lose material even if you had a second attacker that could capture the least-valued defender afterwards.

Jumbo has no SEE yet. For b) and c) it does the following:
- target is defended by a pawn => losing capture
- (rook or queen captures pawn, or queen captures minor piece) and target is defended by a minor piece => losing capture

This leaves the following cases "undecided" so they are currently not classified as a losing capture:
- queen takes rook which is defended by a minor
- queen takes minor which is defended by a rook
- queen takes pawn which is defended by a rook

I should probably add support for these cases as well.

Please don't forget that you can also make use of the losing captures concept in QS: you can simply skip them there to avoid wasting time.

But be careful about positions like this, where there is a sequence of captures, especially in qs:
[d]rnbq1rk1/pp4pp/2pbp3/5pB1/2PPp3/5NP1/PPQ1PPBP/R4RK1 b - - bm exf3; c0 "give up the queen for Halloween.";

I guess that skipping the qs and reducing the depth cause problems in positions like the above.
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 Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First
Subject Author Date/Time
Matthew R. Brades Thu Nov 09, 2017 1:39 pm
Patrik Karlsson Thu Nov 09, 2017 2:44 pm
Matthew R. Brades Thu Nov 09, 2017 3:06 pm
Patrik Karlsson Thu Nov 09, 2017 4:48 pm
Ferdinand Mosca Thu Nov 09, 2017 2:57 pm
Matthew R. Brades Thu Nov 09, 2017 3:19 pm
H.G.Muller Thu Nov 09, 2017 3:40 pm
J. Wesley Cleveland Thu Nov 09, 2017 3:42 pm
Matthew R. Brades Thu Nov 09, 2017 6:49 pm
Sven Schüle Fri Nov 10, 2017 12:23 am
Re: Move ordering Dann Corbit Fri Nov 10, 2017 1:28 am
Sven Schüle Sat Nov 11, 2017 11:40 am
Dann Corbit Sat Nov 11, 2017 9:07 pm
Sven Schüle Sun Nov 12, 2017 11:10 am
Matthew R. Brades Fri Nov 10, 2017 7:00 pm
Alberto Sanjuan Thu Nov 09, 2017 3:59 pm
Jon Dart Thu Nov 09, 2017 8:08 pm
H.G.Muller Thu Nov 09, 2017 8:33 pm

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