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Subject: Re: Question: Fail low at root and time management

Author: John Stanback

Date: 16:04:59 02/08/00

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On February 08, 2000 at 18:24:41, Josť Carlos wrote:

>On February 08, 2000 at 14:28:17, John Stanback wrote:
>
>>On February 08, 2000 at 10:09:27, William Bryant wrote:
>>
>>>I need some recomendations on handling time management when the program
>>>fails low at the root near the end of the alloted search time.
>>>(During game play, not during test suites)
>>>
>>>How do people handle this?
>>>
>>>Do you research the PV move at the lower window (which will return a
>>>move and a score) and then stop?
>>>
>>>Or, do you need to search all the root moves at the lower score to determine
>>>which is truly the best move?
>>>
>>>The later makes more sense, but may consume a significant chunk of additional
>>>time which the program may or may not have.
>>>
>>>Thoughts, ideas and suggestions gratefully accepted.
>>>
>>>William
>>>wbryant@ix.netcom.com
>>
>>If the first move fails low, I increase the time allotment by 10X
>>and then search the remaining moves using the same window, but with
>>a reduced depth.
>
>  I don't understand researching with reduced depth. Won't those moves, with the
>reduced depth, be in the hash table from previuos iterations?
>
>  Josť C.
>

Say I'm searching at depth=10 and the 1st move fails low.  Then I
continue to search all the moves in the list with the same window,
but I reduce the search depth to 8.  You're right, these moves should
be in the hash table, probably with the score being an upper bound
since they were not the best move at previous iterations.  If the
score is below the current alpha value and is an upper bound then
that move can be ignored.  But if the score is above the current alpha
value then it still needs to be searched.  If the 8 ply search comes
back with a score above alpha, then I immediately search it again
to the full 10 ply.

The reason behind this technique is that sometimes the first move
fails low and there are one or more other decent moves.  I think this
method finds these cases faster than trying to get an accurate score
for the first move before searching the rest.  If there aren't any
other decent moves, then often I don't waste too much time doing the full
10 ply search.

>  If any of the remaining moves don't fail low at
>>the reduced depth then I immediately re-search the move to the correct
>>depth.  If I get a move with an ok score (not fail low) at the
>>correct depth and the original search time limit is exceeded then
>>I play that move.  If all moves are searched this way and fail low
>>then the window is lowered and the search procedure starts over.
>>
>>By the way,  I use windowed alpha-beta rather than PVS.
>>
>>John



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