Author: Tom Kerrigan
Date: 16:40:16 10/07/02
1. Deep Blue _did_ do forward pruning. They used null move for threat detection,
not forward pruning, but they did have "domain specific" forward pruning. Hsu
emphasized this quite a bit. He said specifically that it was responsible for
allowing them to search critical variations very deeply.
2. Deep Blue did _not_ have impossibly sophisticated eval terms. Hsu gave two
examples of DB's "extremely costly" eval terms:
i. Seeing if an open file is valuable by calculating the square control of
the 7th and 8th ranks of the file (including rays)
ii. Doing king safety calculations for both sides of the board while the
king is uncastled.
Many PC programs calculate square control and could easily/cheaply implement
(i), and (ii) is not THAT expensive. If king safety takes 10% of a PC program's
time, doing it twice would only make it 10% slower (and only in positions where
kings aren't castled).
Moreover, Hsu said that a major limitation of DB1 (that was fixed in DB2) was
that square control information could only be used for a limited number of eval
terms, apparently because it was available late in the eval pipeline. So there
were limitations to the eval terms that could be computed by DB.
3. There _was_ an implementation of DB's algorithms in software. I asked how the
new eval terms in the DB2 chips were tested & tuned without actually having the
chips, and Hsu said that Joel Benjamin played a "software simulation" to test
them. He made it sound like that should have been obvious. (Are you listening,
Bob?)
4. While he does have the rights to the DB chip design, Hsu is still bound by
IBM NDA for the eval terms and is not legally allowed to disclose them.
-Tom
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