Author: Robert Hyatt
Date: 17:19:22 06/25/02
Go up one level in this thread
On June 25, 2002 at 17:53:11, Ulrich Tuerke wrote: >On June 25, 2002 at 17:42:58, Tony Werten wrote: > >>On June 25, 2002 at 17:30:51, Ulrich Tuerke wrote: >> >>>On June 25, 2002 at 02:40:59, Gian-Carlo Pascutto wrote: >>> >>>>On June 24, 2002 at 18:53:24, Steve Coladonato wrote: >>>> >>>>>>I wonder what you consider 'comparable'. There's no guarantee >>>>>>they'll be similar whatsoever. >>>>> >>>>>That was not a well formed statement on my part. What I meant was that for a >>>>>given ply depth, the evaluation that program X comes up with should be >>>>>comparable to the evaluation that program Y comes up with if both programs are >>>>>fairly equal in overall strength. >>>> >>>>No. There is no guarantee whatsoever that this is true. >>>> >>>>>Therefore, if the algorithms/heuristics that >>>>>program X uses allow it to get to ply M faster than program Y, then program X >>>>>should win if the time allowed constrains how much time each program can use for >>>>>analysis at that depth. For example, if program X can get to ply 11 in 30 secs >>>>>and program Y takes 1 min 30 secs to get there, the overall analysis that >>>>>program X can generate during a game should be better than that generated by >>>>>program Y and program X should win. So it seems that the efficiency of the >>>>>algorithms/heuristics will determine the overall strength of a program. >>>> >>>>Again, this is completely false. >>>> >>>>I will repeat what I said several times earlier in this thread, and that >>>>is that plies are not comparable between chessprograms. The analysis of >>>>one program at ply 11 can be completely different and of higher >>>>quality than another at the same 11 ply. If the second program reaches >>>>ply 11 faster, we have no information at all to make any solid conclusions >>>>about the relative strength of those programs. >>> >>>Completely agreed. This integer which we are talking about should be better >>>called "iteration number". It basically defines how many times the search had >>>been restarted exploiting each time the results of the preceeding iteration in >>>order to extend the search tree. >>>IMHO, the relation of iteration number to search depth is a very loose one, >>>having in mind that todays programs are heavily pruning as well as extending. >>> >> >>Hmm. I can imagine that a program that uses partial ply extensions might decide, >>when the timelimit is almost reached, to start an iteration with only half a ply >>deeper. >> >>Or even worse. Every uses iterative deepening, but did anybody ever prove that >>full plies are best ? Maybe 2/3 ply is better ? > >I think, that I have heard that Junior uses 2 iterations in order to deepen by >one ply. >A long time ago, when watching the main line of David Lang's good old Psion >chess, it seemed to me that David deepens by 2 plies per iteration in Psion >Chess. The length of its PV grew like 3, 5, 7, ... iirc. > >Uli BeBe (Tony Scherzer) also did this. And it turns out to be bad for a couple of reasons. 1. doing odd iterations is a way of trying to make a program more aggressive since the paths have 1 more move for the computer than for the opponent. But with modern programs that extend all over the place, this is not a clear advantage at all since 1/2 the lines might extend by a ply so that 1/2 are 7 ply paths and the other 1/2 are 8 ply paths. 2. It is harder to go from 6 to 7 than it is from 7 to 8 in the old days for basically the same reason. Nowadays it simply costs 9x longer to do 2 plies deeper, rather than 3x longer to do one. Junior doesn't really increment by "2 plies" according to an explanation by Amir a few years ago. He simply counts plies differently. IE a capture may reduce the search by one ply, while a non-capture may reduce it by 2. There- fore, his "plies" are not like our 'plies' even though we both could use the same terminology. Confusing, to say the least... But the overall effect is that he reports significantly larger depths than most while the PVs are going to be about the same length as everyone else.... > >> >>Tony >> >>>Uli >>> >>>> >>>>-- >>>>GCP
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