Author: Ricardo Gibert
Date: 16:28:52 02/27/01
Go up one level in this thread
On February 27, 2001 at 19:17:55, Christophe Theron wrote: >On February 27, 2001 at 18:57:47, Ricardo Gibert wrote: > >>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. > > >I have noticed that ChessGenius for Palm does that. > >I tried with my program Chess Tiger, and the results were bad. I think I have >spent one week on this, and I was disappointed by the results. What explanation did you come up with to account for the disappointing results? > >I notice that Genius for PC does not do that anymore. ChessGenius for Palm is >the 1987 version of Lang's program, Genius for PC is the 1995 version, so it >looks like Lang himself has found it was not such a good idea. > > > Christophe > > > > >>>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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