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Subject: Re: Draw by 2nd repetition?

Author: Dave Gomboc

Date: 15:50:11 04/05/99

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On April 05, 1999 at 17:40:50, Bruce Moreland wrote:

>On April 05, 1999 at 16:29:16, Dave Gomboc wrote:
>
>>On April 01, 1999 at 13:11:29, Bruce Moreland wrote:
>
>>>But what I do is only include *game* position that have occurred *twice*.  A
>>>position that occurs *once* is not included in this table.
>>
>>And you can clear out this table after every non-reversible move, yes?
>
>It is a hash table, not a list.  If I cleared it I would have to reconstruct >it, or copy ir around all over the place.  Since it's a hash table it doesn't >cost a lot to look things up.  The impossible entries don't cause any trouble.
>
>bruce

Hmm... this got me thinking.  I have been keeping track of repetitions in my
awari program by linking back through every second position (but checking for
non-reversible moves on every position).  This method is discussed on the Cilk
Pousse page: http://supertech.lcs.mit.edu/~pousse/#HASH (thanks, Don! :).

But I only do the checking when there are less than eight stones on the board,
because it hurts my search performance quite a bit.  In Awari, the first time a
state is re-reached, the game is decided (by the current material count), so I
don't have the same difficulties that chess programmers have.  So if my normal
hash table is doing the job well (which it isn't really yet, because I haven't
made it two-tier) then I wouldn't have a need for this special hash table.

Well, that's not true either, it will still be faster if I have a small hash
table for actual game positions encountered, assuming that the probe cost
doesn't make it not worthwhile.  (In chess, the probe cost is negligable, but
the overhead of a make-move is *really* low in Awari, and while my program uses
a hash table, some of my classmates found themselves running faster without
one!).

Thanks for the insight.

Dave Gomboc



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