Author: Vincent Diepeveen
Date: 04:32:41 08/02/01
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On August 02, 2001 at 03:44:01, Janosch Zwerensky wrote:
>Hi all,
>
>I read some time ago that Deep Blue wasn't using heuristic game tree pruning
>methods (like, for example, the null-move technique).
>Since null-move was known when DB was around, can anyone here tell why the DB
>team decided not to use it (or wasn't able to do so)?
There are a number of reasons
a) IBM focussed upon nodes a second, search depth was not important,
the only PR argument was their machine was FASTER than anyone elses.
b) they searched 12 ply which was deeper as anyone else anyway
c) nullmove back then was considered dubious, scientists didn't know
much from it
d) look at the historic picture. The deep blue designers were busy
improving their machine. Well they could search deeper as the previous
machine could, so why look to for sure tough to figure out things
like nullmove?
e) in hardware using nullmove is nowadays easier as it was back then.
Back then timing issues were of major importance.
f) Important to realize is that the processors didn't even USE
hashtables.
Bob has given a very plausible explanation. Hsu was busy getting
hashtables to work, but did run out of time to get them to work on
chip.
I can completely imagine Hsu here.
IMHO hashtables are more important than nullmove is,
nullmove only gets important when all the things are well done.
Why get nullmove to work when hashtables aren't working yet?
We all do as if Deep Blue was a well tested and well playing machine.
It was not!
It was not even finished!
What played kasparov were a few bare chips without hashtables even!
No one, including me, could imagine that Kasparov would play a few games
in his life that bad!
Of course, Kasparov is just human, IBM had said all kind of things like
that this would be the last match they would play, "BECAUSE DEEP BLUE
ALWAYS LOST".
It's hard to see this machine as a simplistic thing without political
interests. Instead the most important reasons are completely forgotten
by time: IBM focussed upon NPS.
There were even artificial scientists suggesting
short after the match: "perhaps intelligence is nothing as
a combination of a simple algorithm and a huge processing speed".
Though i completely disbelieve those scientists, the only interesting
thing for Hsu to get to work was a machine getting more nps as any other
machine (his previous version) got.
He made such a machine.
In 1997 i was even completely made a fool at when i suggested that
it was possible with nullmove to search deeper with a huge
nps like DB got, because of a better branching factor when using
a combination of nullmove and clever designed hashtables.
The thread was called something like: "getting 18-20 ply".
I claimed a branching factor which was way under the 'knuth theoretical
branching factor'. In 1997 no one had a good branching factor
except me and some others who very dubiously forward pruned.
This because no one used intensively hashtables in combination with
nullmove.
Of course first nullmove was made ridicioulous, then my claim that
it would be possible to get 18-20 ply with so many nodes a second
(200 million).
You should seek for those messages posted at rec.games.chess.computer
during those years.
Only the furious replies from scientists who still are furiously
commenting here with different arguments in CCC now at different
threads, only those furious replies back then will give you
an impression how weird they back then would have considered
using a combination of nullmove and hashtables as the way to go.
Using nullmove was not even taken seriously.
The big increase in speed of todays processors and the deep blue
logfiles showing it got 11 to 12 ply in most positions, also clearly
showing no depth difference between far middlegame where there are
loads of transpositions, and start of game where there are loads of
branches to research (search depth is
obviously showing that deep blue didn't use
hashtables in hardware processors); if you compare that small search
depth difference between programs using hashtables (with or without
nullmove, whatever) you will clearly see the huge difference
already.
Note that back in 1997 things like multi-probes as we all use,
were also not used by many persons. In fact i only recall Bob mentionning
them he used them in cray blitz.
Best regards,
Vincent
>
>Regards,
>Janosch.
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