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Subject: Re: PB-ON vs PB-OFF (final results)

Author: Ratko V Tomic

Date: 16:24:58 10/16/99

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>>For example, if instead of different time controls you used
>>depth D and D+1 versions, the D+1 will guess correctly the move of D
>>version in every single move, 100% guess rate.

>
> I don't think this is true.  I think the D+1 will ponder different moves
> more than 20% of the time, or maybe more.  Even D vs. D would have about
> 20% pondering difference.  This is because in D vs. D, say one searches
> to 8 ply, then begins to ponder.  The next one searches to 8 ply, but
> it's already one ply ahead of the other, so effectively it was like
> a 9-ply search from the first one.

You're not assuming the _fixed_ D+1-ply vs fixed D-ply rules of game. In this
mode as soon as the given depth is computed program makes a move, it doesn't
take advantage of pondering to geain depth in some given time. If during
pondering it happens to reach its prescribed depth it moves instantly when its
turn comes.

In this mode of play (strictly fixed depth), D+1 has already computed the D-ply
opponent's move and knows exactly, every single time, what it will get in
return, since D-deptyh subtre was a part of his D+1 tree which he picked, and
D-ply oponent (otherwise identical program except for depth) has no choice but
to pick the depth D best move. Yet, the D-ply program will still manage to win
at least 20% of the time.

>> Yet it will lose 20-30 percent of games.
>> Guessing what the opponent will play doesn't mean it will find a
>> correct answer to that move.
>
> But obviously it does most of the time.

Yes, but I find it much more interesting that there are clearly quite a few
positions where deepening the search will make things worse. And that's not one
of those "one in million" patholgical constructs, but perhaps one in 5, in your
everyday vanilla chess positions. Which means, they can be sought or created
more systematically than just intuitively when we're lucky. Imagine taking on
Fritz 5.32, or any other top program, and getting 8 or 9 points out of 10
regularly, even though your old friends at the chess club still beat you as
always.




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