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Old April 22nd 04, 09:33 PM
Jean-François GAZET
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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 :

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

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


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Old April 28th 04, 06:15 PM
David Richerby
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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.


David Richerby Homicidal Vomit (TM): it's like a pile of puke but it wants to kill you!
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