Author: Robert Hyatt
Date: 15:36:03 02/27/01
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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.
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