Author: Sune Fischer
Date: 02:07:45 01/21/04
Go up one level in this thread
On January 20, 2004 at 21:41:47, Robert Hyatt wrote: >On January 20, 2004 at 19:21:04, Sune Fischer wrote: > >>On January 20, 2004 at 13:09:04, Robert Hyatt wrote: >> >> >>>>Are you saying a 5 ply PV on position X is good, but when we later in some other >>>>parts of the tree search X with ply 5 or above the PV will be nonsense? >>> >>>Absolutely. I explained why. One sequence of 5 moves might have two checks. >>>Another sequence to reach the same position might have no checks. Which >>>resulting search will be more accurate? The one without the preceeding checks >>>or the one following the checks? Think about "draft". >>> >>>> >>>>I think you need to explain that to me very carefully. >>> >>>Done. :) >> >>No you haven't explained anything, it's exactly the same calculation! > >No it isn't. read _very_ carefully. > >I search a-b-c-d-e-f-g-H and reach position H in a 10 ply search. When I get >to H, the remaining depth is 3, except moves a e and g are checks. So the >remaining depth is 6, this is the draft. > >Now I search g-f-e-d-c-b-a-H and again I get to position H. But with this >order of moves, there are no checks. The remaining depth is 3. > >Same position, same ply, different draft, different result when you search >position H. Which do you search first? Again, same position, but with a >different sub-tree hanging below that position. That is _not_ "exactly the >same calculation." Trees are strange things, in reality. Hmm, I think you are the one who should read very carefully, I specificly said: "search X with ply 5" which means the PV was produced by a 5 ply search, so that means the _remaining_ depth is 5. :) You can check the two remaing depth against eachother and make sure it isn't less accurate than what you need. But actually, your example is interesting as well. Say we concatenate two PVs, one very much shorter than the other (from a much less deep search), why should that give us problems? They are both PVs so seperately they are ok, why shouldn't they be ok together? I suppose it is possible the window is way off in one case (e.g. a mate window) and somehow getting mated turns into a PV which we then glue up with a PV from a different window showing a draw score.. :) But I suspect this would be unusual, basicly I don't see how the same position can produce such different yet _exact_ scores?? >>A-ha! >>If you recorded qsearch I can understand why you saw nonsense..:) > > >Not only q-search. See previous example. > >The hash is path-independent. The tree below a node is _not_ path >independent, from repetition to 50-move-rule to search extensions that >may or may not be done depending on the order of moves in the path. Yes that's true, that is always an issue with the hash. I think it is a small issue in this context though, "grasping for straws" come to mind :) -S.
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