Reply
 
LinkBack Thread Tools Display Modes
  #1   Report Post  
Old April 22nd 04, 09:33 PM
Jean-François GAZET
 
Posts: n/a
Default extensions

Good morning,

i'm trying to add extensions to my engine. I'm using a classical alphabeta
function :
int alphabeta(int depth, int alpha, int beta)
depth is dicreased 1 by 1 :
eval=-alphabeta(depth-1,-beta,-alpha);

At the beginning at the function alphabeta(), if king is incheck, i do
++depth. This works fine.

In the main move loop, if do a ++depth on a promoting move, juste before
calling -alphabeta... the engine searches for ever when the first promoting
move is found. Then, if i add "if depth1" or 2, i don't see any
improvment.

I don't understand how engines like GnuChess can write : depth+=DEPTH when
extending.
(DEPTH is 12).

Regards.


  #2   Report Post  
Old April 28th 04, 06:15 PM
David Richerby
 
Posts: n/a
Default extensions

Jean-François GAZET wrote:
I don't understand how engines like GnuChess can write : depth+=DEPTH
when extending. (DEPTH is 12).


It may be using `fractional plies'. Certain features of the position
would be worth a fraction of a ply extension so that, while one of those
features won't trigger an extension, a combination of them would. For
example, if you decided that giving check was worth half a ply of
extension and promoting a pawn was worth three quarters of a ply,
promoting with check would be worth 1.25, so would trigger a one-ply
extension, but promoting without check or checking by some other means
wouldn't give a promotion. (This is a silly example but it should give
the idea.)

Fractional plies are most efficiently implemented by scaling so one ply
might be depth four, meaning that depth 2 is half a ply and so on.

I've not looked at the GNUchess source so I don't know if that is what
it's doing but I thought I'd post this anyway for general education.


Dave.

--
David Richerby Homicidal Vomit (TM): it's like a pile
www.chiark.greenend.org.uk/~davidr/ of puke but it wants to kill you!
Reply
Thread Tools
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Search extensions and transposition tables Delphi rec.games.chess.computer (Computer Chess) 2 August 21st 03 10:10 PM


All times are GMT +1. The time now is 01:43 PM.

Powered by vBulletin® Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright ©2004-2019 ChessBanter.
The comments are property of their posters.
 

About Us

"It's about Chess"

 

Copyright © 2017