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

Author: Josť Carlos

Date: 00:16:18 02/09/00

Go up one level in this thread

On February 08, 2000 at 19:04:59, John Stanback wrote:

>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.
>>>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.

  Thanks for the explanation. I'll think about it :)

  Josť C.

>>  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.

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