From: Jerry Donald Watson <j1.donald1@gmail.com>
Date: Sun, 12 Aug 2018 07:47:30 +0000 (+0200)
Subject: Simple razoring: depth 1 only, no distinction between PV / NonPV
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=348cd5ed74e808733545c392d1bd80965a379617;hp=348cd5ed74e808733545c392d1bd80965a379617

Simple razoring: depth 1 only, no distinction between PV / NonPV

We simplify the razoring logic by applying it to all nodes at depth 1 only.
An added advantage is that only one razor margin is needed now, and we treat
PV and Non-PV nodes in the same manner.

How to continue?
- There may be some conditions in which depth 2 razoring is beneficial.
- We can see whether the razor margin can be tuned, perhaps even with a
  different value for PV nodes.
- Perhaps we can unify the treatment of PV and Non-PV nodes in other parts
  of the search as well.

STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 5474 W: 1281 L: 1127 D: 3066
http://tests.stockfishchess.org/tests/view/5b6de3b20ebc5902bdba0d1e

LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 62670 W: 10749 L: 10697 D: 41224
http://tests.stockfishchess.org/tests/view/5b6dee340ebc5902bdba0eb0

In addition, we ran a fixed LTC test against a similar patch which also
passed SPRT [-3, 1]:

ELO: 0.23 +-2.1 (95%) LOS: 58.6%
Total: 36412 W: 6168 L: 6144 D: 24100
http://tests.stockfishchess.org/tests/view/5b6e83940ebc5902bdba1485

We are opting for this patch as the more logical and simple of the two,
and it appears to be no less strong. Thanks in particular to @DU-jdto
for input into this patch.

Bench: 4476945
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