From: Marco Costalba <mcostalba@gmail.com>
Date: Thu, 4 Apr 2013 19:53:59 +0000 (+0200)
Subject: Increase null verification threshold to 12 plies
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=889922041be317f26a2547498b6751ed55f0ee22

Increase null verification threshold to 12 plies

Increasing depth limit to 10 plies seems stronger
after 16K games at 15"+0.05 (ELO: +3.56) and also
repeating the test at 60"+0.05 TC:

ELO: 2.08 +-3.1 (95%) LOS: 90.9%
Total: 16000 W: 2641 L: 2545 D: 10814

Moreover setting the limit to 12 is proved stronger
then limit set to 10 by direct SPRT test at 15"+0.05:

ELO: 2.56 +-2.0 (95%) LOS: 99.5%
Total: 46568 W: 9240 L: 8897 D: 28431

So we directly set the limit to 12, the strongest setup.

bench: 4361224
---

diff --git a/src/search.cpp b/src/search.cpp
index ab346734..1abe022a 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -679,7 +679,7 @@ namespace {
             if (nullValue >= VALUE_MATE_IN_MAX_PLY)
                 nullValue = beta;
 
-            if (depth < 6 * ONE_PLY)
+            if (depth < 12 * ONE_PLY)
                 return nullValue;
 
             // Do verification search at high depths