Author: Ricardo Gibert
Date: 15:57:47 02/27/01
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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. That makes sense. How about a slight modification: Let's say you decide not to try N + 2, due to lack of time. You could still decide to do N + 1 and thus only have the odd-even problem on the last ply. When you don't have time to do N + 1, then you've avoided the odd-even problem completely. > >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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