Re: computer-go: Zobrist hash random?

[Don Dailey <drd@xxxxxxx>]

Hi Wolfgang,

I  don't quite  understand  your post,  you  have left  out  a lot  of
the detail,  but I think  you probably  misunderstood the  posts about
using "random numbers."

The random  numbers ARE indeed a  set of well  chosen constants.  They
are not generated during the  search, but by the programmer in advance.   

I AM a  chess programmer and I know that  almost all chess programmers
use the  Zobrist hash function.   Some chess programmers (such  as Bob
Hyatt  of Crafty who  is also  a computer  scientist) build  the table
off-line  using  the  hamming  distance  algorithm I  described  in  a
previous post.  This table is  compiled into the program a fixed table
of numbers  or constants as you  seem to be describing.   My own chess
program does it the same way.

There are  infinite possible hashing  functions, but I'm not  aware of
any that improve  on Zobrist in terms of  simplicity, speed or quality
of  key distribution,  and these  3  qualities are  what make  Zobrist
hashing so popular.

If you  could give me  more details about  your idea, I would  like to
compare to see if we are talking about the same idea or not.

Don





   Date: Fri, 13 Sep 2002 13:29:51 +0200 (MEST)
   From: nr997@xxxxxxxxxxxxxxxxx
   X-Priority: 3 (Normal)
   X-Authenticated-Sender: #0011807033@xxxxxxxxxxxxxxxxx
   X-Authenticated-IP: [80.135.21.23]
   X-Flags: 0001
   Content-Type: text/plain; charset="us-ascii"
   Sender: owner-computer-go@xxxxxxxxxxxxxxxxx
   Precedence: bulk
   Reply-To: computer-go@xxxxxxxxxxxxxxxxx

   Hi Friends

   Always i read here to take random numbers for the hash function.
   That is not the best way. You take well choosen contants.
   For example there should not be numbers like a,b,c where a xor b = c in my 
   set of constants, for advoiding too early hash collisions. 
   That is one of the main advatages of this hash function not to have
   collisions too early.
   So you have ...
   Ask some good chess programmers, they know. 
   So it is granted not to have the same hash value for positions which differs

   only (a few stones more or less) little.
   For a tree search you want to have it.

   Always i read such nonsense of random numbers.
   ...

   Have fun 
   Wolfgang

   -- 
   GMX - Die Kommunikationsplattform im Internet.
   http://www.gmx.net