Welcome to GameHourz.com!
FAQFAQ   SearchSearch      ProfileProfile    Private MessagesPrivate Messages   Log inLog in

discrepancy in alpha-beta

 
   Game Forums (Home) -> AI Games RSS
Related Topics:
[REQUEST] Minimax alpa beta algorithm for Othello games - any body help me please... i want to implement minimax alpa beta algorithm for othello games... anybody have the source code.... please share it to me, please ;-) please mail me at Thanks for alllllll ;)

TBC Fast Package(1-70) - Any Class Free 2000G - Wow per level per level. Dear Sir or Madam Hot Sale!For all of our news and are some Special Package! We now provide measured by..

A* and multi-goals - Hello, I am using A* to find the shortest path in a 3D I have waypoints at each rooms, points to create the graph. At the moment I can select a start and goal node, the A* algorithm do the rest and my

bigtest - bigtest

AI and C# - HI all... does anybody know a book about AI, which includes examples in c#? thx for reading ;)
Next:  alpha beta  
Author Message
bob

External


Since: Sep 19, 2005
Posts: 71



(Msg. 1) Posted: Mon Sep 19, 2005 8:43 pm
Post subject: discrepancy in alpha-beta
Archived from groups: comp>ai>games (more info?)

I noticed some pseudocode from wikipedia
(http://en.wikipedia.org/wiki/Alpha-beta_pruning) that does these
checks in alpha beta:

min:
if beta <= alpha return alpha

max:
if beta <= alpha return beta

Then there's code at
http://www.cs.dartmouth.edu/~rus/courses/AI/AI-03/Lectures/l6.html that
says this:

min:
If beta >= alpha return alpha

max:
If alpha >= beta return beta


As you can see, the checks for min differ. Anyone know who's right?

 >> Stay informed about: discrepancy in alpha-beta 
Back to top
Login to vote
Michael C. Horsch

External


Since: Sep 20, 2005
Posts: 1



(Msg. 2) Posted: Tue Sep 20, 2005 7:26 am
Post subject: Re: discrepancy in alpha-beta [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

When alpha < beta, things are "normal". When alpha >= beta, the current
path can be pruned.

When you are maximizing, you are trying out a bunch of potential moves
for max, which means you are looking at a bunch of new alpha values.
Then you test a new alpha value against the current beta value. So if
you find a violation of alpha < beta, you return the alpha immediately.

When you are minimizing, you are trying out a bunch of of new beta
values associated with min's move. Here you test the current alpha
value against each new beta value. If you find one that violates alpha
< beta, you return it immediately.

So it looks like Wikipedia is correct here, and the test for min
in the Dartmouth notes is in error (possibly a typo).

Mike

 >> Stay informed about: discrepancy in alpha-beta 
Back to top
Login to vote
bob

External


Since: Sep 19, 2005
Posts: 71



(Msg. 3) Posted: Tue Sep 20, 2005 10:01 am
Post subject: Re: discrepancy in alpha-beta [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

It looks like Wikipedia is correct. BTW, your explanation has some
mistakes. In max, you return beta if alpha < beta is violated.

Michael C. Horsch wrote:
> When alpha < beta, things are "normal". When alpha >= beta, the current
> path can be pruned.
>
> When you are maximizing, you are trying out a bunch of potential moves
> for max, which means you are looking at a bunch of new alpha values.
> Then you test a new alpha value against the current beta value. So if
> you find a violation of alpha < beta, you return the alpha immediately.
>
> When you are minimizing, you are trying out a bunch of of new beta
> values associated with min's move. Here you test the current alpha
> value against each new beta value. If you find one that violates alpha
> < beta, you return it immediately.
>
> So it looks like Wikipedia is correct here, and the test for min
> in the Dartmouth notes is in error (possibly a typo).
>
> Mike
 >> Stay informed about: discrepancy in alpha-beta 
Back to top
Login to vote
Display posts from previous:   
   Game Forums (Home) -> AI Games All times are: Ekaterinburg, Islamabad, Karachi, Tashkent (change)
Page 1 of 1

 
You can post new topics in this forum
You can reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum



[ Contact us | Terms of Service/Privacy Policy ]