Author: Uri Blass
Date: 10:38:53 07/05/02
Go up one level in this thread
On July 05, 2002 at 12:50:34, Robert Hyatt wrote: >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... A change can be a good change even if I solve part of the positions slower. If I solve more position at every time control then it means that the change is probably a good change. It is also possible to learn from positions that I do not solve about better rules when not to prune. Uri
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