Author: Andrew Dados
Date: 09:32:12 09/16/99
Go up one level in this thread
On September 16, 1999 at 04:49:15, Bas Hamstra wrote: >On September 15, 1999 at 19:42:34, Andrew Williams wrote: > >>On September 15, 1999 at 17:12:16, Dan Homan wrote: >> >>>I was reading the crafty source again the other day and noticed that >>>Bob has a special function to improve the move ordering at the root >>>of the search. >>> >>>I really didn't feel like writing such a function last night, but I >>>thought instead to use the values returned by the search itself to >>>improve the move ordering at the root. I know that I only get an >>>accurate value for the best move, but I thought that my fail-soft >>>search might return useful numbers for the other moves as well.... >>> >>>Implementing this was pretty quick and easy: there were a couple >>>of pit falls, but the total changes were about 5 lines of code. >>>Previously I simply used the same move ordering at the root that I >>>use at all other nodes. >>> >>>The improvement was amazing! I got a full ply in many positions and >>>about a half-ply in many more. It improved my solution times on WAC >>>noticably and seems even better in quiet positions. >>> >>>I know that my solution was a quick kludge, so I am wondering what >>>other people do for move ordering at the root of the search. >>> >>> - Dan >> >>Hi Dan, >> >>This is what I used to do. (I'm also using fail-soft). It's one of those >>things that shouldn't really work, but seems to do very well. However, >>I later changed it to use the number of nodes in the sub-tree to order >>root moves. If I recall, this made very little difference to my program's >>performance; I just prefer this, because I know why it should work. > >Interesting. Isn't this in fact the same discussion as a few days ago? Using >values < Alpha for movesorting? In this case on the root. > >Well, if it shouldn't work, why does it, if it does, if you know what I mean? >And if it works, I would very much like to hear Bob's reaction. > >Anyway I will try this too. > > >Regards, >Bas Hamstra. Explanation why fail-soft scores work is actually easy. Imagine 2 moves with *true* scores for that ply of (alpha-10) and (alpha-100), respectively. Your fail-soft will more likely return score for second move lower then for first move (there is that <alpha-100,alpha-10> score space which *can not* be returned from search of first move, but can return from search of second move). Second move will also more likely require less nodes to refute. So those 2 methods are comparable, and ordering by fail-soft scores works just because probability of scores is non-random (higher chance that worse move will return worse score, cause it has more 'score space' for that)... I wonder why Bob neglects that... -Andrew-
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