Author: Dann Corbit
Date: 18:04:53 09/15/00
Go up one level in this thread
On September 15, 2000 at 17:57:47, Gian-Carlo Pascutto wrote: >On September 15, 2000 at 17:13:57, Dann Corbit wrote: > >>Sorry. Only 24 coming. This is only solved to 15 ply. Checkmate or not, you >>must complete the ply to claim the "prize". >>;-) > >Quote: > >Here are a set of tough positions to search deeply. Just finding a mate is not >good enough, uless you can *prove* it is the shortest mate. > >>1.f6+ Kh8 2.Qh6 axb2+ 3.Kb1 Ne6 4.dxe6 Qxa2+ 5.Nxa2 Rg8 6.hxg6 >> +- (#9) depth: 15/21 00:00:18 436kN > >If you want a _proof_ I guess CHEST is the only option. > >Now, before you start writing those poems realize that this >analysis is done by a Solution-Tree-Cost search and *not* by >an alpha-beta searcher. > >The ply depths listed are totally uncomparable to alpha-beta >ply depths. > >If you think this is cheating, consider that that measuring >ply depth, via any algorithm at all, is a bogus measure. So! I've been bamboozled. I think that pruning that leads to the same solutions is valid. Every sort of pruning will throw away some correct solutions. But NULL move is only very rarely going to lead to problems. As for extensions like quiescense and things of that nature -- they lead to better solutions but I don't think the added depth should be used to increase the ply estimate. >The only thing that might qualify is a fixed-depth, not pruned >except by alpha-beta, search. Those won't reach 16 ply within >the next few years I guess ;) Which was exactly my point. However, for NULL-move pruned searches, it appears that two of the difficult problems I posed were solved. A third would have been solved, but Dieter felt mercy. I think the nature of my request was fairly obvious. The notion that "ply depth means nothing" is bogus because everyone obviously knows exactly what I mean. But let me temper it. If a pruning extension that leads to an examination of fewer leaves proves to be superior in providing correct answers after a thorough statistical test for the same estimated depth in plies, that extension would be accepted. >Every more or less standard chessprogram uses some kind of >extensions or pruning, which make the ply depth figure _meaningless_. >As meaningless as NPS is as an indicator of program strength. I disagree. Let's call ply the number of half-moves that a program is examining on a minimum (ignoring NULL-move pruning). That is a completely unambiguous term that anyone can understand. Now, if a program uses extensions to see farther along certain special tracks, that is not a ply depth but a speculation to improve the guess at the current ply. On the next iteration, we will have moved to the next ply. >Even worse, there exist very good algorithms that don't have >any notion of ply depth at all. What algorithms are those that do not consider half moves from the origin? >Besides, the basic task you gave us was very badly worded too: >SOLVE these positions. Solve in the following manner: A program which has exhaustively searched 16 plies will have a material and positional value computation. The value of that computation is calculated in centipawns according to the PGN standard. You will find that after reaching a certain depth, good programs generally agree on the evaluation (certainly within a pawn or so). >A real solution would only consist of one thing: 1, 0, or -1. >Now, ironically, the one solution you didn't accept was the only >one I was able to solve... (to a 1) That's an interesting real solution, but it isn't the one that I asked for. >Instead you ask for a value (centipawn evaluation) that is >also meaningless. Centipawn = 1/100 of a pawn ? But the >value of a pawn is NO constant! I made no such claim. However, centipawns is a measure approved of in the PGN standard. An unblocked pawn on the 7th rank is worth far more than 100 centipawns, obviously. >The only thing that matters >is whether the position is WON or LOST (or drawn). Is that what your evaluation function returns? I doubt it. >I hope you now realize that this challenge was flawed, and >that there is no use to holding ply-depth DSW's. I disagree. You can refuse to perform the request (which I think was fairly obvious) but others might find it interesting. Claiming that there is no such thing as a ply depth is even more silly than claiming that all programs have the same meaning for depth in plies. The problem is one of definition. If you cannot use an ephemeral definition, just use the exhaustive one. It's a bit more doubtful you'll come up with useful data, but I think everyone really knows what I mean. I realize that programs do prune differently. However, at whatever the author really believes are the strongest play settings they do have some idea of what half move they are processing, I am sure, for any algorithm. If not, where is the algorithm so that I can read about it? >PS. >My own program Sjeng reached over 12 ply in 30mins on 5 of >those positions on my Cyrix120, so it's likely that a fast PentiumII >can solve them. Also, the matefinder was on to something in at >least one other position (not the mate above though!). I will >try to get a full 16 ply search tomorrow. But again I ask you >to realize that '16 ply' is meaningless. The only reason why Sjeng >is able to get to those depths faster than e.g. Crafty (on the positions >I tested this was the case) is that Sjeng is very light on extensions, >but heavy on pruning. A 16 ply Crafty search is totally uncomparable >to a 16 ply Sjeng search. You can replace Crafty and Sjeng by any >random chessprogram in that last sentence. When Christophe Theron said that we were close to being able to search 16 plies in a game, what do you think he meant? Were his words meaningless? I don't think so. Each ply (in my definition) is a half-move carefully examined by the program [in such a way that the optimal chances of winning from performing the analysis in that manner are performed]. We could search forward and narrow our search to a single move at each ply forward. But that does not fit my definition, since anyone can see that such a method leads to disaster rather than the optimal chance of winning (unless you're the GM who said, "I only consider one move -- the best one." when asked how many moves they think of).
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