Author: Christophe Theron
Date: 21:01:45 05/19/98
Go up one level in this thread
On May 18, 1998 at 21:18:24, Dave Gomboc wrote:
>On May 18, 1998 at 18:12:53, Ren Wu wrote:
>
>>
>>On May 18, 1998 at 17:14:10, Carsten Kossendey wrote:
>>
>>
>>>First of all, your output does in no way state which scores are bounds
>>>and which are exact, so everyone will assume they are *all* exact.
>>
>>First of all, you != everyone. So you is you, please don't confuse
>>youself to everyone, which is a big mistake i think.
>>
>>>Secondly the point of the position was that Bxa8 is a *really* bad move,
>>>and a score of <= +3.81 is not exactly suggesting this. Crafty's +0.56
>>>eval (contrary to +3.16 for b6) gets a lot closer to the point, for
>>>example.
>>
>>When you know a move no good, it is little interets to find out exactly
>>how bad it is, especially if you found another move is better.
>>
>>I will not answer any follow up on this thread, because i found little
>>info it contains. What i want say at my orignal post is that a program
>>with little king safety knowledge can find the correct move at 9ply, and
>>i don't understand why other top program have difficulties.
>>
>>I have little interests to prove my program is stronger than others, it
>>is not at the moment. I am more interested in why those programs have
>>diffculties.
>>
>>And i am happy that my program did good job at this position.
>>
>>Ren (renw@iname.com)
>
>I have a hard time believing that the +3.81 for Bxa8 was an upper bound,
>not an exact score. It was the first move searched at that ply level.
>Unless you're doing something strange, that move will be resolved to a
>score before alternatives are looked at.
>
>Dave Gomboc
No Dave. You don't know what he is doing is his program. I don't either.
But a standard implementation for alpha beta with aspiration could
behave this way. That is, if the first move in the list fails low (has a
score below alpha), the program doesn't try to compute the exact score
and PV for this move, and goes directly to the others moves without
showing any PV.
So he may choose, at this time, to display the first move with a
(default) score equal to alpha (the lower bound), just to show what's
happening, or display nothing at all.
If no other move is able to bring the score into the alpha beta window,
the search starts again with a lower window.
For example, in case of a fail low, Chess Tiger displays nothing after
the first move has been searched. If another move manages to bring a
score inside the window, this move and PV is displayed, as if it was the
first to have been searched (it may look strange when you follow the
computations, but it's OK).
If no move is able to bring the score above alpha, Tiger displays
"Oops..." (self explanatory I think) and starts the search again with a
lower window. You can easily imagine that I hate to see this message...
:)
There are others ways to do it, that's why you shouldn't draw
conclusions just by seeing a program's log file.
The only thing that can be trusted (I believe) is the first move of the
PV. Everything else (rest of the PV, score) can be wrong in a particular
program. For example, it seems that Deep Blue's PV cannot be trusted
(and it's going to take a century or 2 to explain that it can happen,
and that it doesn't prove any cheating on DB side).
Christophe
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.