Computer Chess Club Archives


Search

Terms

Messages

Subject: hamming distance...

Author: martin fierz

Date: 06:14:40 04/07/04

Go up one level in this thread


On April 07, 2004 at 08:56:26, James Swafford wrote:

>On April 07, 2004 at 06:55:31, Andrew Williams wrote:
>
>>On April 07, 2004 at 06:49:59, Renze Steenhuisen wrote:
>>
>>>
>>>Hi all,
>>>
>>>could someone give me some numbers that are common with hashkey collisions?
>>>Because I guess my % is little too high...
>>>
>>>I'm getting like 0.03% [which is 1 every 3000, if I'm not mistaken]
>>>
>>>This is when using TT=32MB (haven't got the exact number of entries)
>>>
>>>If you think it is an error, any suggestions on where to start looking?
>>>
>>>Thanks!
>>>
>>>   Renze
>>
>>One in 3000 seems very high. How many bits are there in your hashkey?
>>
>>Andrew
>
>
>Even though you said you're using Crafty's random num gen,
>I would start by doing some hamming-distance checks.
>
>For reference, my program gets:
>Checking minimum hamming distance between random keys: 14 bits
>Checking average hamming distance between random keys: 31 bits
>
>If your hamming distances are comparable, you can conclude
>your zobrist keys are ok, and go from there.
>
>--
>James

i never understood why people think hamming distance is a good measure for the
quality of random numbers. e.g. for 8-bit numbers i can produce a collision with
the numbers

a = 11111000
b = 11100011
c = 00011011

because b^c = a. the mutual hamming distances all come out to 3-5 :-)

cheers
  martin



This page took 0 seconds to execute

Last modified: Thu, 15 Apr 21 08:11:13 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.