Author: David Rasmussen
Date: 16:31:13 12/06/01
Go up one level in this thread
On December 06, 2001 at 08:29:44, Sune Fischer wrote: >On December 06, 2001 at 08:12:22, David Rasmussen wrote: > >>>Perhaps your hashing scheme _is_ the problem, maybe that is why my results are >>>better. >>> >> >>Perhaps it is. Talk about that to Hyatt. It's his program. > >Ok, well its not so strange you have the same collision rates then. > What do you mean? What I am describing in _this_ thread is Crafty, look at the subject. I was talking about Crafty all along. I have mentioned several times, though, that I have a similar problem in my own program when using 32-bit pawn hashing. But I assume my scheme is not the problem as I am doing the same thing everybody else is doing, as far as I know, except maybe for the PRNG. The PRNG that I use is one of the best in the world (probably overkill for this purpose), but I have tried with several with the same results. > >>Anyway, I think you need not worry about me understanding the math. After all, I >>study math. I know of the birthday problem. It's not necesarily relevant here. > >Okay, then try and calculate the odds of getting 300 collisions out of 10000 >using "danish: tilbagelægning" from a pool of 4 billion, those odds are >astronomically small for sure, so something strange _is_ happening. > I don't necesarily think that that is an accurate model for the situation here. I trust my emperical data. It's the model that needs to be fixed IMO. >>Sequences of chess positions following the chess rules are not random. They have >>redundancy. > >No, but even if the positions are very similar the keys should be vastly >different, this is also one of the ideas of using the zobrist table. > True. >>I don't. This is not hard evidence. This is theory based on false assumptions >>and a wrong model. > >Feel free to name 1! :) > >>Hard evidence is hundreds (or thousands or millions if you >>want) of pairs of positions that has the same pawn hash signature in Crafty. >>That is by definition a collision. > >Maybe so, but you think you are proving that 32 bit keys are no good, when all >you are proving is that you have _some_ bug IMO. > Then a lot of us have the same bug. We see exactly the same behavior. Same rates, bursts of clusters of collisions etc. >>Could there be a problem with Bob's random >>numbers? Sure, but I doubt it. Also, when we talked about a 32-bit hashing >>scheme we both meant a "simple" one. That is, one where you generate random >>numbers, not one where you handpick every number. Surely there is some linear og >>non-linear algebraic code of high dimension that will have fewer collisions than >>"good" random numbers, but, we were talking about random numbers, which is what >>"people" use. Hyatt admits it is not good enough. I would like to see Bruce do a >>similar experiment. > >Me too, espicially since it was him who talked Bob into it in the first place;) He's not really sure. >But you've seen my results and they confirm "my theory", so that would be a very >strange double bug in any case. > Your program stands out, then. >>Talk to Hyatt about that. As for me, I have tried many different PRNG's. All >>with similar results. > >It is very strange indeed, but 32 bit seems to be working for me (for what ever >reason), so I will change from 64 to 32 soon :) > >-S. That's understandable. Just be sure you don't have a buggy test, as you are implying that I have. /David
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