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Subject: Re: Repeatability (questions for Omid)

Author: Bruce Moreland

Date: 13:30:25 12/19/02

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On December 19, 2002 at 11:24:44, Robert Hyatt wrote:

>>1) When the null-move search comes back with fail high, and verify is true, I
>>will do a regular search with reduced depth.  If this search fails high, I cut
>>off like normal.  If this search does not fail high, I have to re-search with
>>the original depth.  What I don't understand is what I do if the initial reduced
>>depth search modified alpha.  I am assuming that I put alpha back the way it was
>>and start over.
>
>That is how I did it, yes..
>
>
>>
>>2) I don't know if this implementation allows two consecutive null moves or
>>what.  In specific, I don't know what "null_ok()" does.  I am assuming that if I
>>don't allow two null moves in a row already, I can continue to not allow two
>>null moves in a row.
>
>
>I did it just like my normal program.  No consecutive null-move searches, and
>I did continue to use the "avoid-null" hash table trick as well.
>
>
>
>>
>>3) I am assuming that if the search cuts off when doing the reduced depth
>>searches, that the depth record in the hash table should be the original depth,
>>and not the reduced depth.
>
>That is what I did, although it seems that it might be a problematic
>assumption that I didn't give much thought to since the code already worked
>that way normally...

I think you are thinking about a different area.  In Omid's pseudo-code, he
takes the main "depth" variable and decrements it.

If he's off doing a search, and fails high, he has to record hash for this node
and cut off.

The depth value has been decremented, so unless he puts it back, he's going to
store a "9" in the hash table even though he entered this node with a "10".

In my implementation I never decrement depth, so I don't have this problem.
What I do instead is remember that I'm in this state, so rather than passing
"depth - 1" to the recursed search function, I pass "depth - 2".

Omid suggested that I remove the re-search idea since it is a zugzwang
optimization.  I tried that and performance was almost identical to R=3, which
in Gerbil's case is not better than R=2.

I'm going to continue tweaking with this, but for now I have some related ideas
testing in Ferret.

bruce



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