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Subject: some null-move questions

Author: martin fierz

Date: 03:35:57 09/25/04


well, as promised here are questions 4-7 of a zillion. perhaps i should also add
that the train ride from zurich to brissago takes about 3 hours and that i have
a centrino laptop, so i need some input :-)

nullmove questions!

1) do you save "don't nullmove" in your hashtable? if yes, how much does it help
you? isn't this a tinytiny improvement, since if you do nullmove, and it fails,
you have to research a much larger tree?
you would be saving "don't nullmove" if your nullmove fails, right?

2) related: do you save matethreat in your hashtable? is this not another
tinytiny improvement?

3) some people advocate not to nullmove if the side to move has few (mostly 0,
perhaps also 1?) pieces. i realize that zugzwang is a problem for nullmove, but
is it a real problem as far as games go? isn't it possible that in pawn endgames
doing a nullmove would lead to a few embarassing losses, but help overall?

4) i never thought much about verified 0-move pruning. but a post i read last
week made me think: i always thought i could do the following:

if(pieces > 0)
  if nullmove-fails-high
    return value;
if(pieces == 0)  // do a verification search
  if nullmove-fails-high
     verify result with a normal search with reduced depth.
       if verification-search-fails-high
          return value;

now there was this post saying that this won't work because you have to disable
the nullmove in your entire verification search. i don't understand why that
would be? can somebody explain?

cheers
  martin



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