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 Post subject: A discussion about AIPosted: Wed Feb 20, 2008 5:54 am
 SON OF A GUN

Joined: Mon Nov 01, 2004 5:41 am
Posts: 11605
We don't really have a "theory section" and I don't think we should, because the PP isn't a horribly overrun section and it wouldn't hurt to keep them together... so I am going to start a thread on AI. On the homework that I just turned in lastnight, there was this question (With my answer) I am curious as to what everyone's thoughts are:

Q:Sometimes there is no good evaluation function for a problem, but there is a good comparison method: a way to tell whether one node is better than another, without assigning numerical values to either. Show that this is enough to do a best-first search. Is there an analog of A*?

A:The idea behind a best-first search is that it chooses each successor / child node based on some rule that defines which nodes are better than one another, typically a function f(n). As long as the comparison method provides a way to determine if one is better than another then a best-first search can be performed choosing each node in succession based on it being better than another. Due to A* being classified as a best-first search and there is a way to qualify a better node from a less ideal node; one could construct a function/method to track each paths overall status related to how â€œgoodâ€

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 Post subject: Re: A discussion about AIPosted: Fri Feb 22, 2008 2:09 am
 Bitchin' Fast 3D Z8000*

Joined: Tue Jun 29, 2004 11:32 pm
Posts: 2555
Location: Somewhere between compilation and linking
Not bad. You should probably scratch out a C with that answer. =)

Are you using the green someone and Norvig AI book? If so, which chapter and question number?

I should have some time on Saturday to get into it.

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 Post subject: Posted: Fri Feb 22, 2008 6:57 am
 SON OF A GUN

Joined: Mon Nov 01, 2004 5:41 am
Posts: 11605
http://aima.cs.berkeley.edu/

I think it was 4.12.

That wasn't the only one on the assignment. I will post my whole HW thing here (should be safe, it was due Wed, and he doesn't give partial credit/late credit...) 4.2, 4.3, 4.11, and the question above, 4.12. His biggest thing is mostly about demonstrating an understanding, after I talked to him... that seemed to be his biggest thing, even if our numbers/answers aren't quite right... although there isn't much in the way of partial credit, so either you get it or you don't.

4.2 wrote:
The heuristic path algorithm is a best-first search with the objective function: f(n)=(2-w)*g(n)+ w*h(n) For what values of w is this algorithm guaranteed to be optimal? What kind of search is performed for the following values for w?
w = 0 â†’ f(n)=2*g(n)
w = 1 â†’ f(n)=g(n)+ h(n)
w = 2 â†’ f(n)=2*h(n)

This algorithm will be found to be optimal for any values of w that make the h(n) portion of the function negligible if it is not already admissible. If it is overestimating the distance from the goal it would be made optimal for w = 0. This happens because w = 0 removes h(n) from the decision function removing the effect of overestimating the distance. This also makes it most like a uniform-cost search, which is optimal by its definition. For w = 1 it will also be optimal provided that h(n) is admissible. If h(n) is admissible it will also be optimal for w = 2 as it is going to choose the nodes who are closest to the goal and the factor of two out in front will not change the order they are expanded in.

For w = 0 :: f(n)=2*g(n)
This removes the â€œestimated distance from the goalâ€

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 Post subject: Posted: Tue Mar 11, 2008 9:04 am
 Bitchin' Fast 3D Z8000*

Joined: Tue Jun 29, 2004 11:32 pm
Posts: 2555
Location: Somewhere between compilation and linking
I am dying to get into this... but life keeps throwing up road blocks... :\

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 Post subject: Posted: Tue Mar 11, 2008 12:10 pm
 Java Junkie

Joined: Mon Jun 14, 2004 10:23 am
Posts: 24245
Location: Granite Heaven
I am dying to get into this... but life keeps throwing up road blocks... :\

Ditto.

I love having great conversations in this folder, and I bitch about their absence when I have the time to participate. Then, when they pop up, I find I don't have time to contribute.

Sorry Crash ...

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 Post subject: Posted: Fri Mar 14, 2008 11:01 am
 SON OF A GUN

Joined: Mon Nov 01, 2004 5:41 am
Posts: 11605
Jipstyle wrote:
Sorry Crash ...

Don't worry, this class has given me plenty of ammo. Fortunately, I figured out his trick, or at least a trick, to get a decent grade on the HW.

He is kind of stingy.

I have my A* in LISP written...

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