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Subject: Re: Instability thing...

Author: Sune Fischer

Date: 08:34:28 09/18/04

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On September 18, 2004 at 07:02:22, Andrew Platt wrote:

>On September 18, 2004 at 04:05:38, Sune Fischer wrote:
>
>>
>>I decided to try out the triangular PV thing Bob
>>speaks so highly of, to see if it improves move ordering...
>>
>>I was careful to terminate the PV on all exact scores - of course.
>>Still I was getting illegal moves in the PV.
>>
>>It turned out to be a hash/nullmove problem.
>
>There's no score that could be responsible for having illegal moves in the PV.
>There are two main things I had to take care of to get rid of illegal moves:
>
>a) Make sure you truncate the PV for the ply you are entering before you start
>doing a null move / iterating through the move list / internal iterative
>deepening, etc.. In other words before you do anything that will increase the
>current ply. Obviously since you are using a triangular array, you aren't
>touching the PV stored higher up when you do this.

This might work, but I think you have to update the PV instantly on all new PV
nodes, otherwise you will overwrite the child PV at the next move.

Currently I wait with the PV copying to the end of that node when all the moves
have been searched, then I only have to update the PV once (or maybe not at all
if there is a FH move before that).

>b) If you update the PV in qsearch and you can generate illegal moves there, you
>will have to take special action. I just don't update the PV in qsearch which is
>the easy way out!

No PV in qsearch. I doubt it is worth it, it would have to be a test for another
day. :)

-S.
>Andy.



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