Author: Vasik Rajlich
Date: 03:39:23 05/27/04
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On May 26, 2004 at 13:49:38, Tord Romstad wrote: >On May 26, 2004 at 13:34:23, Robert Hyatt wrote: > >>I have used "IID" for years, but in a very restricted way, namely to handle the >>case along the PV where I have no hash move. I've never tried it _everywhere_ >>before, so have no data. But I intend to try to see if it is something that >>could work, or if it is a waste... > >I am fairly sure you will find that _everywhere_ is a waste. It is probably >not worth doing near the leaf, you have a hash table move to search, or when >a fail-low is most likely. Perhaps you should also use a somewhat bigger >reduction factor than in your "along-the PV IID". > >Note that it could also be interesting to look for good ways to make use of the >return value of the internal search. It gives a reasonably reliable estimate >of the value of a full-depth search, and can be useful as an ingredient in >pruning tricks. The most obvious (and entirely risk-free) case is when the >reduced-depth search returns a mate score. When this happens, it is clearly >not necessary to do a full-depth search. > >Tord Yes, there is lots of room for playing with IID. Note that 95% of all nodes fail high in some way, so you can be pretty aggressive. The IID principle can also apply to some additional situations: 1) You have a hash move, but it's at depth-2 rather than depth-1. You can do another IID layer in this case. 2) Your fail-high hash move (for some engines the only possible kind of hash move) fails low. Here you can do IID to get an alternative move. And - as Tord mentioned - an IID search can be turned into the final reduced-depth search, based on its result. Vas
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