Author: Uri Blass
Date: 17:04:29 06/27/03
Go up one level in this thread
On June 27, 2003 at 19:48:44, Sune Fischer wrote: >On June 27, 2003 at 19:04:04, Steve Maughan wrote: > >>Sune, >> >>>Perft is no good speed indicator anyway, not even for a move gen. >>>The perft tree is so different from the chess tree. >>> >>>Optimizing for perft is basicly like building a formula 1 car to use for >>>off-road rally. >> >>I don't agree. Perft is *quite* a good thing to optimize. There are really >>four fundamental foundations of a good chess program - >> >>1) Evaluation >>2) Move Ordering >>3) Make / Unmake moves >>4) Generate Moves > >This "box" thinking is not optimal I think. >It is better to think like this: > >strength = engine(eval,moveordering,make/unmake,genmoves,...); > >There is no reason why you shouldn't be mixing them, like e.g. in Rebel. > >>There are of course other elements (e.g. extension) but these four elements IMO >>are the key elements. Perft directly measures the performance of the last two >>elements. Some would say that the speed of move generation is not that >>important and this is true to a certain extent since time spent in the GenMove >>routine is often less than 10%. However, if you can generate moves quickly you >>will most likely also be able to generate mobility quickly - an element of the >>evaluation function. So I would argue that perft goes some way to measuring >>three out of the four factors I've listed. > >I can't think if a simple analogy here, so I will give you a mathematical >example. > >Find the maximum of f(x,y) for x,y in [some interval]. >You can think of x as move generator and y as eval. > >If you know that f(x,y)=g(x)+h(y) for some functions g and h, then you can find >max for f by maximixing g and h. > >However you do not know such functions exist, and there is no reason to believe >they would. In my experience hybrid functions tend to be the most powerful >solutions. > >If you are determained to get the fastest possible make move, then that excludes >the use of attack tables, this will come back to haunt you in the search and the >eval. And this is also counter productive for perft because if you have fast make move then you cannot use attack tables for faster move generation. I believe that this is the reason that Movei was faster than Sharp in calculating perft. IMO it's very clear that it makes little sense to optimize a >makemove+movegen without considering the remaining program. I agree but I think that the difference between the things is not big. > >Suppose you use 50% of the time in eval and 20% in makemove+movegen, now you >slow down makemove a factor two but speed up eval also by a factor two. >Would you not think of this as a good decision? I would. Yes but for calculating perft the speed of the move generator is also important and if I make my makemove slower then I can make my movegen faster. for perft 2 I make only the legal moves in one ply but generates the legal moves of all the games of 2 plies. > >>It's other advantage is that you can't cheat with perft - i.e. for any given >>position there is a certain number of nodes that represent perft 5. This is in >>contrast to Node Per Second where it's not clear what constitutes a node. So >>you can see and objectively measure your perft times against other engines. > >Yes nps doesn't compare, you can't compare speeds that simple in chess progs, >the best you can do is time to solution, or of course play matches. > >What is really misleading about perft, is the topology of the search space. >It is very artificial compared to a realistic tree. You know in perft that you >will be needing all the moves you generate, you never generate a wasted move. >If you optimize for this, you are setting up your engine to go fast on the wrong >track. I make/ummake moves at the last ply in perft, that means my genmove takes >only 10-15%, the remaining 85% is pure make/unmake, as can be seen in a profile. > >If I wanted a fast perft I'd only have to optimize my makemove, if I could move >the big load into genmove I'd go a lot faster. No It is better for you not to make the last ply but only generate legal moves. However in a *real* search you >don't get to make all the moves you generate, so that means the genmoves would >profile-wise be just as important as makemove, perhaps. In real perft I also do not make most of the moves that I generate so you see that for me it is similiar. Uri
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