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Subject: I need help with Search/Selective Extension

Author: scott farrell

Date: 17:38:05 08/24/02


Guys,

Chompster is still going slow, but let's see if we can make it search
smarter.

I have the basics if SE going.

If any of these, I do a serach extension
single legal move,
null move returns -INFINITY,
isCheck,
recapture

The search extension is just doing  search(-beta,-alpha,depth) instead
of search(-beta,-alpha,depth-1)

It seems to work OK. It solved one of my hard test positions in one ply
less, but in about the same time, as it used many more nodes.

My questions:
- I cant work out the impact on the hash tables. For example, if when
eventually return to the root of the tree, after a few SEs, and we store
the value in the hashtable, what depth should we put on it? If we are
searching all moves to 3 plies, and do 2 SE's during a particular branch
search, should I not store it in the HT as depth=5 (and how do I work
out depth=5?)
- should there be a limit on how SE's you do. I know crafty does "no
more than one ply of extensions are allowed at any one level in the
tree". But it depends how how you look at "any one level in the tree",
given SEs play around with the tree, as what this really means.
- I found I just burned more nodes, and time, and generally about 5%
worse on WAC for 1 and 2 seconds/position
- I run all the calcs to determine if to do a SE (see above) before I
iterate the moves and doMove (other than recapture which doesnt make
sense without a move). I am unsure as to test things like isCheck before
or after doMove.

Scott
sfarrell@icconsulting.com.au
sfarrellc(ICC)



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