Author: Robert Hyatt
Date: 17:53:00 01/21/04
Go up one level in this thread
On January 21, 2004 at 18:21:28, Tord Romstad wrote: >On January 21, 2004 at 14:14:00, Robert Hyatt wrote: > >>On January 21, 2004 at 13:34:27, Tord Romstad wrote: >> >>>Yes. This is why it is a good idea not to do IID at all nodes, but only >>>at nodes where you are reasonably sure that there will be a fail high. >>>You should always check the value of the static eval before doing the >>>internal search. >> >>I don't even think you want to do it at fail-high nodes. Just at nodes >>where you expect a "true score". At least that is how _I_ have implemented >>it. > >I use MTD(f), hence I *never* get any "true scores" anywhere in the tree. Why? I played with mtd(f) for several months right after Don Daily started his "you got to try this" many years ago... I got exact scores, because the last two searches have a common "edge" and that "edge" is the true score. > My >intuition >regarding PVS is not very good (I have used MTD(f) almost since the beginning), >but >I don't see any reason not to use IID at all expected fail-high nodes in a PVS >search, >too. At a fail-high node, you can return a value before all moves are searched. > If >your move ordering is perfect, you will only need to search one move. It >therefore >makes sense to make some extra effort to make sure that the first move searched >will really return a score >= beta, and the most obvious way to do this is to >first >do a search with reduced depth. What am I missing? > for the majority of moves, it is easier to find a capture refutation than to do an N-iteration search... I tried it both ways (plus other ideas) when I first did this. What I am doing right now has really proven to be effective with no particular down-side or risk... For normal fail-high positions we have already been doing iterated searches for previous depths, so hopefully we get decent ordering here most of the time using normal ideas. The critical positions are the PV nodes, because there searching a good move first is not good enough. We need the _best_ move first. At normal fail-high positions, we only need a move good enough to cause a cutoff, not the best move. IID will provide the best move generally, but at significant cost. >Another thing that has always puzzled me is that reducing the depth by only 1 >ply >gives better results for me than reducing by 2 plies, like you and almost >everybody >else do. I have tested this very thorougly, and depth-1 always seems to be a >bit >better. Really weird. I tried it both ways years ago. I found the depth-2 worked better for me. I ran the test set (a bunch of positions) with IID off, using D-1 and D-2, and I chose the case that produced the shortest time overall... for me that was D-2. I should probably test it again just to see if things have changed, as it is certainly possible after so many versions under the bridge. :) > >Tord
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