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Combine increased LMR horizont and fixed null move reduction

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Set null move reduction to R=4, but increase the LMR horizon
to 3 plies. The two tweaks are related and should compensate
the combined effect of null move + LMR reduction at shallow
depths.

Idea from Tord.

After 999 games at 1+0

Mod vs Orig  +251 =522 -225 51.30% + 9 ELO

On Tord iMac Core 2 Duo 2.8 GHz, one thread,
Mac OS X 10.6, at 1+0 time control we have:

Mod vs Orig 994-1006  -1.4 ELO

But Orig version is pgo compiled and Mod is not.
The PGO compiled version is about 8% faster, which
corresponds to about 7 Elo points. This means that
results are reasonably consistent.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2009-07-13 13:35:29 +01:00
parent b8326edea3
commit 2a203d8d6f
1 changed files with 2 additions and 3 deletions
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5
src/search.cpp
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@ -1243,9 +1243,8 @@ namespace {
StateInfo st; StateInfo st;
pos.do_null_move(st); pos.do_null_move(st);
int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID); Value nullValue = -search(pos, ss, -(beta-1), depth-4*OnePly, ply+1, false, threadID);
pos.undo_null_move(); pos.undo_null_move();
@ -1364,7 +1363,7 @@ namespace {
// Try to reduce non-pv search depth by one ply if move seems not problematic, // Try to reduce non-pv search depth by one ply if move seems not problematic,
// if the move fails high will be re-searched at full depth. // if the move fails high will be re-searched at full depth.
if ( depth >= 2*OnePly if ( depth >= 3*OnePly
&& moveCount >= LMRNonPVMoves && moveCount >= LMRNonPVMoves
&& !dangerous && !dangerous
&& !moveIsCapture && !moveIsCapture