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Subject: Re: Question for the MTD(f) experts

Author: Richard Pijl

Date: 02:53:21 04/14/04

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On April 14, 2004 at 05:38:17, Tord Romstad wrote:

>On April 14, 2004 at 05:32:37, Richard Pijl wrote:
>
>>>So my next question is, how do you normally populate a hash table with PV nodes,
>>>since we only get edge values during the search?  Do I need to follow the pv
>>>from hash to hash with a makemove for each succeeding pv node?
>>>{ICK}
>>
>>In addition to storing the move that gets a fail high, you could also store the
>>bestmove (i.e. score with highest value below alpha) in the hashtable. This only
>>makes some sense with fail soft. With fail hard (as TSCP is) you will (almost)
>>always get alpha as best value so the chosen move will be random.
>>
>>That way you will be able to construct an estimation of the pv, which will
>>improve with each iteration.
>
>Does this really work for you?  I once tried it, and the results were ugly.  In
>my experience, it is never a good idea to store a best move except when failing
>high.
>
>Tord

The last time I tried, it did. But I see how it could deteriorate moveordering.
Perhaps I should take a little bit closer look when I get home. It seems a waste
to ignore it, but perhaps the cases where the bestmove on a fail low are stored
should be selected a bit more careful, e.g. only when score<alpha and it is the
only move with that score (so all others are likely to be worse).
I still think it might be useful for PV construction though.

Richard.



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