Author: Dave Gomboc
Date: 00:01:27 11/10/03
Go up one level in this thread
On November 09, 2003 at 20:36:08, Robert Hyatt wrote: >On November 09, 2003 at 12:01:25, Dave Gomboc wrote: > >>On November 08, 2003 at 11:09:35, Robert Hyatt wrote: >> >>>On November 07, 2003 at 14:14:58, Dave Gomboc wrote: >>> >>>>On November 07, 2003 at 14:14:08, Dave Gomboc wrote: >>>> >>>>>On November 06, 2003 at 22:31:49, Robert Hyatt wrote: >>>>> >>>>>>On November 06, 2003 at 20:43:58, Dave Gomboc wrote: >>>>>> >>>>>>>On November 06, 2003 at 19:46:29, Robert Hyatt wrote: >>>>>>> >>>>>>>>On November 06, 2003 at 11:22:54, Dave Gomboc wrote: >>>>>>>> >>>>>>>>>On November 06, 2003 at 09:47:32, Robert Hyatt wrote: >>>>>>>>> >>>>>>>>>>On November 06, 2003 at 08:33:49, Gian-Carlo Pascutto wrote: >>>>>>>>>> >>>>>>>>>>>On November 06, 2003 at 05:45:53, Renze Steenhuisen wrote: >>>>>>>>>>> >>>>>>>>>>>>Depth-First Algorithms: >>>>>>>>>>>> AlphaBeta (Fail-hard, Fail-Soft) >>>>>>>>>>>> MTD(f) >>>>>>>>>>>> >>>>>>>>>>>>Best-First Algorithms: >>>>>>>>>>>> SSS* >>>>>>>>>>> >>>>>>>>>>>The distinction between the three (and best-first and depth-first) >>>>>>>>>>>is very hazy, read "Research re: search and research" by Aske Plaat. >>>>>>>>>>> >>>>>>>>>>>-- >>>>>>>>>>>GCP >>>>>>>>>> >>>>>>>>>> >>>>>>>>>>Eh? The distinction is _huge_. >>>>>>>>>> >>>>>>>>>>One searches the tree in one direction and requires very little memory. The >>>>>>>>>>other searches the tree in another direction and requires huge memory. >>>>>>>>>> >>>>>>>>>>I'm not sure how you could say that the distinction is very hazy. They >>>>>>>>>>are as different as night and day... >>>>>>>>> >>>>>>>>>However, MTD(infinity) is equivalent to (searches exactly the same tree as) SSS. >>>>>>>> >>>>>>>> >>>>>>>>That's fine. A best-first (breadth-first) search can search _exactly_ >>>>>>>>the same tree as a minimax (depth-first) search also. Doesn't mean a >>>>>>>>thing about how similar the two approaches are, however... >>>>>>>> >>>>>>>>However, the trees are grown differently. I don't think any book I >>>>>>>>know of uses the actual search space as a way to define a search >>>>>>>>strategy... >>>>>>>> >>>>>>>> >>>>>>>>> >>>>>>>>>http://www.cs.ualberta.ca/~jonathan/Grad/plaat.phd.ps >>>>>>>>> >>>>>>>>>Dave >>>>>>> >>>>>>>Fine, but the point is that in this particular case, they are not as different >>>>>>>as night and day. :-) >>>>>>> >>>>>>>Dave >>>>>> >>>>>>They are different in the base algorithm. They are different in their >>>>>>memory requirements. They are different in the order in which they search >>>>>>the tree. They are different in how hashing may (or may not) work. >>>>> >>>>>They are *NOT* different in the order in which they search the tree. The >>>>>traversal order is identical. >>>> >>>>More accurately, the node expansion order is identical. >>>> >>>>DAve >>> >>> >>>Which specific depth-first vs breadth-first algorithms are you comparing >>>when you make that statement? >> >>The ones GCP mentioned: mtd(oo) and SSS. mtd(-oo) and DUAL also have identical >>node expansion order. >> >>Dave > > >Yes, but _only_ in bizarre cases. mtd(f) searches the same basic >tree multiple times to hone in on the score. At least two searches >are required, at an absolute minimum. Generally it requires more. > >Also it beats me how _any_ best-first algorithm could search the same >tree as any depth-first algorithm, except for pathological cases... Appendix B of Aske Plaat's Ph.D. thesis contains specific details demonstrating that SSS and mtd(oo) "evaluate the same leaf nodes in the same order when called upon the same minimax tree". Reference #106 from that thesis is a technical report that contains the formal proof. Dave
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