Author: Christophe Theron
Date: 16:20:48 02/27/01
Go up one level in this thread
On February 27, 2001 at 18:36:03, Robert Hyatt wrote:
>On February 27, 2001 at 17:08:16, Alvaro Jose Povoa Cardoso wrote:
>
>>By definition the iterative deepening procedure calls Search() several times,
>>and each time it increments _Depth_ by one.
>>But what if we increment by two?
>>Isn't a waste of time stepping just one ply deep at a time?
>>In my checkers program, I increment _Depth_ by two (2,4,6,8,10,12,14,16...) and
>>it seams to work better than stepping by one ply (2,3,4,5,6,7,8,9,10,11,12,...).
>>Surely a previous search at _Depth-2_ gives a good PV to try first at this
>>iteration.
>>Comments anyone?
>>Does this aply to chess?
>>
>>Thank you
>>Alvaro Cardoso
>
>
>There are a couple of issues:
>
>1. each iteration takes about 3x as long as the previous if you increment
>depth by 1. If you increment depth by 2, then each iteration will take about
>9x as long. If iteration N takes 1 minute, you have a target of 3 minutes,
>you will choose to not try N+2 as there is no hope of finishing it. It actually
>makes more sense to go in .5 ply increments near the end of the search since
>that gives you a better chance of finishing an 12.5 ply search when a 12 ply
>search would be too quick and a 13 ply search would take too long.
>
>2. BeBe did odd ply searches. The reason was to eliminate the odd-even
>problem where odd ply searches are aggressive, even ply searches are more
>passive. But he had the problem described in 1 above.
The idea is interesting but if you have a QSearch then you have no control on
where (odd or even) the search stops. So BeBe's way will not work if you have a
QSearch.
And what about extensions? You think you are going to do an even ply search,
then a check extension happens and you end up doing an odd depth search!
Christophe
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