A Gross Miscarriage of Justice in Computer Chess (part four)
22.05.12
Rajlichs comment is notable for both its brevity and its significance. The
first realization one makes is that the whole PST case in actual playing terms
is a trivial sideshow whatever the merits of the ICGAs assertions. PSTs, per
Rajlich, have no material impact on playing strength and possibly no measurable impact within standard statistical confidence levels. Rajlich is evidently not
even sure himself based on his remark that PSTs are probably a positive factor.
To be efficient the PSTs should use at most two or three CPU cycles. This explains
why Fruit and Rybka evaluations were based on PSTs with simple integer patterns
(e.g. +1, +0, -1, -3); integers are quicker than floating-point numbers. None
of the PSTs had been optimized in Rybka 1.0 Beta, hence their simplicity. Both
Fruit and Rybka 1.0 Beta use PSTs that were generated through the use of simple
formulas that reflected then-common chess knowledge. Even though Rajlich recognized
that PSTs had only a tiny impact he still wanted to have the ability to fine-tune
his evaluation. There was no demonstrated intent to obfuscate Fruit integers
in Rybkas code as is stated in the ICGA report.
Source: Chessbase News