Author: Robert Hyatt
Date: 09:50:34 07/05/02
Go up one level in this thread
On July 05, 2002 at 11:29:08, Uri Blass wrote: >On July 05, 2002 at 11:00:14, Tony Werten wrote: > >>On July 05, 2002 at 00:17:09, Uri Blass wrote: >> >>>On July 04, 2002 at 22:26:44, Robert Hyatt wrote: >>> >>>>On July 04, 2002 at 11:57:11, Uri Blass wrote: >>>> >>>>>On July 04, 2002 at 10:07:37, Robert Hyatt wrote: >>>>> >>>>>>On July 04, 2002 at 03:49:40, Uri Blass wrote: >>>>>> >>>>>>>On July 03, 2002 at 14:29:17, Robert Hyatt wrote: >>>>>>> >>>>>>>>On July 03, 2002 at 13:46:17, Christophe Theron wrote: >>>>>>>> >>>>>>>>>On July 02, 2002 at 20:20:37, Robert Hyatt wrote: >>>>>>>>> >>>>>>>>>>On July 02, 2002 at 18:54:49, Keith Evans wrote: >>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>>Sorry to be anal retentive, but that's a bit of a stretch. Here's what they say: >>>>>>>>>>> >>>>>>>>>>>"The chess chips optionally support the use of an external FPGA (Field >>>>>>>>>>>Programmable Gate Array) to provide access to an external transposition table, >>>>>>>>>>>more complicated search control, and additional terms for the evaluation >>>>>>>>>>>function. In theory this mechanism would have allowed the hardware search to >>>>>>>>>>>approach the efficiency and complexity of the software search. Null move search >>>>>>>>>>>was also explicitly supported by this method. Due to time constraints, this >>>>>>>>>>>capability was never used in Deep Blue." >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> >>>>>>>>>>Read on. On page 67, section 4.1, item 3, "mate threat". >>>>>>>>>> >>>>>>>>>>"It is relatively simple using a null move search to detect if there is a >>>>>>>>>>threat in the current position.... The Deep Blue implementation ... >>>>>>>>>> >>>>>>>>>>Which matches what I said. They had support for a normal null-move search >>>>>>>>>>had they wanted to use it, but they did use null-move to detect threats, >>>>>>>>>>something that has been done before (and several of us use a form of mate >>>>>>>>>>threat extension based on this idea presently). >>>>>>>>>> >>>>>>>>>>So they used null-move in at least one way, without using it as a forward >>>>>>>>>>pruning algorithm, which fits with Hsu's "no errors in the search" theme he >>>>>>>>>>mentioned repeatedly over the years. Extra extensions were one thing to him, >>>>>>>>>>but outright errors were something else not to be tolerated. Right or wrong. >>>>>>>>>>I obviously disagree about the errors in a normal null-move search, but I >>>>>>>>>>can hardly argue with their success... >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>>That's my point as well. >>>>>>>>> >>>>>>>>>I don't argue about their success. >>>>>>>>> >>>>>>>>>I'm just saying that they succeeded because their chips were very fast. So fast >>>>>>>>>that they allowed them to use inferior search techniques and still succeed. >>>>>>>>> >>>>>>>> >>>>>>>>Could you not make the _same_ statement about chess 4.0 in 1975? Until that >>>>>>>>point _everybody_ was doing forward pruning like mad. They discovered that a >>>>>>>>a shallower full-width search had fewer errors and they stomped everybody into >>>>>>>>the ground until everyone converted... >>>>>>> >>>>>>>It is different. >>>>>>>It is obvious that selective search from the first plies >>>>>>>is a mistake when you have speed. >>>>>>> >>>>>>>It also seems obvious that pruning rules that are based >>>>>>>on the remaining depth is a good idea and you can use them >>>>>>>and see everything if you search deep enough. >>>>>>> >>>>>>>Uri >>>>>> >>>>>> >>>>>>Everybody is overlooking an _important_ detail, so lets take this back to >>>>>>CS101: >>>>>> >>>>>>1. Forward pruning is a form of selective search. You cull moves you think >>>>>>are no good, so that the rest are basically "extended" or searched deeper than >>>>>>the "lemon" moves. >>>>>> >>>>>>2. Search extensions do _exactly_ the same thing. They extend the moves you >>>>>>think are "good" so that they are searched more deeply, while the ones you >>>>>>do not extend are not searched that deep. >>>>>> >>>>>>In simple terms, the two ideas are _identical_ in every way, as far as the >>>>>>final result. To say that doing a full-width search with lots of very >>>>>>sophisticated extensions is not as good as doing a sophisticated selective >>>>>>search (forward pruning) is not a particularly sensible statement to make. >>>>>> >>>>>>_anybody_ that has spent any time on tree-searching will realize that _either_ >>>>>>will produce _exactly_ the same result assuming the extensions and forward- >>>>>>pruning are done with the same skill level. >>>>>> >>>>>>So picking on this aspect of deep blue is simply a strawman argument. They >>>>>>clearly do more extensions than the rest of us. Which _may_ offset their >>>>>>lack of forward pruning. Believing or claiming anything else shows a lack >>>>>>of understanding of something... >>>>>> >>>>>>As far as your selective search comments, It is obvious (to me) that everybody >>>>>>is not doing selectivity just deeply in the tree. It is being done near the >>>>>>root as well, based on some very trivial oversights that some programs make from >>>>>>time to time. Oversights that a 4 ply full-width search would see. >>>>> >>>>>Yes >>>>> >>>>>I also do selective search in movei by null move pruning >>>>>and I think that it is a mistake >>>>>but I have more important mistakes to correct in movei >>>>>so I do not care about it now. >>>>> >>>>>pruning deep in the tree and extensions are not the same >>>>>because the lines that the deeper blue team did not prune >>>>>were not only stupid lines but also quiet lines. >>>>> >>>>>searching lines that appear to be bad lines >>>>>and quiet lines to the same depth is a mistake. >>>>> >>>>>Uri >>>> >>>> >>>>Selective pruning and selective extensions are _identical_ in result, different >>>>in implementation. Searching bad and quiet lines to the same depth is fine >>>>so long as you search critical lines to a deeper depth... >>> >>>If you search bad line to smaller depth relative to quiet lines you can get a >>>speed improvement. >>> >>>searching everything to at least depth 12 seems to me a waste of time even if >>>you can search 200M nodes per second. >>> >>>It is better to search bad lines to depthes 8-13(depending how bad is the line >>>and if the final position is a quiet position) and quiet lines to depth 14. >> >>Wich would be the same as searching to 14 ply and prune to 8 or >>searching to 8 ply and extending to 14. >> >>OR searching to 11, prune to 8 and extend to 14 ( guess what, there are even >>more possibilities depending on how strong you prune or extend ) >> >>Tony > >You missed my point. > >My point is that the programmers of deeper blue did not search bad lines to >smaller depth relative to quiet lines and even if you can search 200M nodes per >second it is a mistake to do it. But they _did_ do this. They did all sorts of extensions, from singular, to threat moves, to you-name-it. That extends non-quiet moves, while leaving the quiet moves alone. I don't think it so easy to quantify a move as "bad". Just look at WAC141 and tell me how that queen move looks good to _any_ surface analysis. Yet it wins. Pruning that could lose the game if you are black. Or miss winning it if you are white... I don't buy the concepts of "bad", "quiet" and "tactical". I prefer "extendable" or "non- extendable" instead... > >Not pruning based on evaluation is a big mistake because in a lot of the lines >that the computer searches one side is losing material for no compensation. Again, WAC141 is the perfect counter-example to this... > >It is espacially the case if null move pruning is not used. > >Pruning positions based on evaluation and the question if the position is quiet >can also help to find practical sacrifices faster. > >It was the first pruning that I tried in Movei(even before null move pruning). > >Uri
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