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Subject: Nullmove verification search

Author: Scott Gasch

Date: 15:26:40 07/25/02


Hi,

I recently reworked my hash tables to be more efficient and found, to my
surprise, that my engine could not longer solve FINE70.  Well I hunted this down
and found that it was not a hash bug but rather a problem with an addition I
made a while ago: a nullmove verification search.  The idea (which may be a bad
one, it seems) is to _always_ nullmove (even in late endgames) but before
accepting a FH after null search, do a reduced depth search to verify the FH
result.

It seems like this works very well in some positions (and has the side effect of
allowing you to do a zugzwang extensions when the nullmove search FH and the
verification search does not).  But it royally screws up the FINE70 position.

My question for other programmers around is: is there anyone else playing with
this null verification search and how are your results / impressions?

Scott



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