Author: Johanes Suhardjo
Date: 11:48:57 07/13/98
I'm very lazy to post this message, but since I got the idea from CCC,
I feel obliged to post the result. Some of you may find this completely
nonsense, for that: sorry! For others, your comments are welcome.
Frank's idea was "If a move is illogical compared to the two previous
moves, search it with a shallower depth, if it's score > alpha then
re-search with a normal depth, otherwise drop the move from search list."
For the definition of illogical move, look at his article on June 21.
I adopted Frank's idea, with a couple of modifications:
1. I only look at the last move (not two).
2. Since I don't keep attack_to board (very expensive, I just calculate
square_attacked on the fly), I define something called influence board
which is: (attack_from[sq][queen] | attack_from[sq][knight] |
one_mask[sq]) -> pre-computed.
So if (((one_mask[from] | one_mask[to]) &
(influence[last_from] | influence[last_to])) == 0) then prune.
I know this is like a voodoo magic, that's why I said "sorry!" above.
This is parrot's result running WAC on an Sun Ultra 30.
Before: TOTAL: 292/300, tss = 33280 second^2
After : TOTAL: 292/300, tss = 29083 second^2
where tss is sum of square of the time to solution (in second square).
I have been running parrot for several nights on FICS and haven't seen an
indication if it plays better or worse. The reason I'm still keeping the
pruning is that on one position (Bratko Kopec (sp?) #12) which I use for
sanity check, the tree size improved so much (for 9 plies):
Before: 2176761 nodes in 42 seconds
After : 1515774 nodes in 30 seconds
P.S. I think this pruning is very similar to razoring, only razoring is
comparing with beta, and this pruning has a more strict condition:
Frank's illogical move or my influence board.
Johanes Suhardjo (johanes@farida.cc.nd.edu)
--
Sweater, n.:
A garment worn by a child when its mother feels chilly.
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