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Subject: Re: Q: Fail High percentage

Author: Robert Hyatt

Date: 19:22:24 12/08/00

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On December 08, 2000 at 20:41:40, Landon Rabern wrote:

>On December 08, 2000 at 16:16:01, Robert Hyatt wrote:
>
>>On December 08, 2000 at 13:21:21, Peter Fendrich wrote:
>>
>>>On December 08, 2000 at 13:06:43, Robert Hyatt wrote:
>>>
>>>>On December 08, 2000 at 12:56:09, Peter Fendrich wrote:
>>>>
>>>>>I looking for a measurement for move generation performance.
>>>>>
>>>>>Do you think FH/CountNodes, where FH is number of times the first generated move
>>>>>was a Fail High, is a good measurement?
>>>>>Do you have some other?
>>>>>What's your figures?
>>>>>I get some 50% and I have a feeling it's to low.
>>>>>
>>>>>//Peter
>>>>
>>>>
>>>>The critical statistic I measure in crafty is this:  "For any position where
>>>>I 'fail high' (return a score >= beta) what percentage of the time does it
>>>>happen on the _first_ move?"  I generally average 92%.  Anything over 90% is
>>>>reasonable.  Anything less means move ordering needs work.
>>>
>>>OK, it seems logical. I have in princple 3 types of FH:
>>>  1) Hash table (without moving)
>>>  2) Null Move
>>>  3) Ordinary moves (including the hash table move)
>>>
>>>Do you include all these cases?
>>>With only the third case counted I'm well over 90%
>>>
>>>//Peter
>>
>>
>>Only 1 and 3.  2 is done at a different place in the search and doesn't
>>really count in "move ordering".
>>
>>Actually, the way you wrote it, only 3 counts.  for 1) you are not searching
>>a move, so that can't be counted.  2) doesn't count either...
>
>I am getting about 80% on this, is this real bad?  I am not doing internal
>interative deepening, do you think this will help a lot, or do you think there
>is something else wrong.
>
>I try moves in this order:
>
>hash/pv
>all captures sorted MVV/LVA
>two killers
>3 history scan moves
>the rest
>
>
>Regards,
>
>Landon W. Rabern


Your MVV/LVA ordering is probably the culprit.  Because you are trying moves
like QxP, even though the pawn is defended... and you try those _before_ you
try the move that will ultimately fail high (a killer or history move).

I would still expect it to be higher than 80%... but that might be about right
with MVV/LVA.  You get some of that back in terms of faster ordering, and you
get some back because the bad captures get cut off quickly by null-move
searches... but it could be better...




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