Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!zaphod.mps.ohio-state.edu!think.com!spool.mu.edu!snorkelwacker.mit.edu!hsdndev!husc6!purdue!ccncsu!longs.LANCE.ColoState.EDU!ah314368
From: ah314368@longs.LANCE.ColoState.EDU (Vincent Huffaker)
Newsgroups: comp.ai
Subject: Re: What is "fuzzy logic"?
Message-ID: <13842@ccncsu.ColoState.EDU>
Date: 29 Mar 91 17:40:55 GMT
References: <1991Mar28.192533.3272@waikato.ac.nz>
Sender: news@ccncsu.ColoState.EDU
Reply-To: ah314368@longs.LANCE.ColoState.EDU (Vincent Huffaker)
Organization: Colorado State U. Center for Computer Assisted Engineering.
Lines: 63

>This is a novice question. I've read precisely one article on
>"fuzzy logic" so far that was at all informative, and the
>understanding I got from it goes like this:

>* Traditional feedback systems are analog in implementation. Their
>control signals can be characterized as analytic functions of their...

>* With computers, it becomes possible to have control outputs
>which are arbitrary combinatorial functions of present and...

>* "Fuzzy logic" lies somewhere between a purely analytic and
>an arbitrarily combinatorial form; control functions are now....

>Does this agree with what other people understand by "fuzzy logic"?
>If so, there isn't really anything in it that can be described
>as "fuzzy". Please correct me if I'm wrong.


Recently, I've also been wondering about fuzzy logic and just what it is. 
There's been an incredible amount of hype about it.  If a reporter doesn't 
understand the logic behind something, it suddenly becomes "fuzzy-logic".
According to all the sources, Japan loves it and America doesn't care about 
it (so, of course, America is behind).  There's supposed to be new 
cameras coming out that use "fuzzy-logic" for their auto-focusing mechanisms.

As for your description, I've never heard of fuzzy logic being described as 
a analog-digital hybrid before.  But then again, I've never heard any
satisfactory descriptions of fuzzy-logic (I'm still thinking about yours).
All the times I've heard about it, its description has sounded like 
conditional logic (or probabilistic logic).  All the reports talk about 
how now you can define "fuzzy" sets like (short, medium, tall, very tall) 
rather being restricted to two-valued sets (true, false).

In normal logic, if you have a set (say a set of tall people), then a person
is either in the set or not in the set.  There is no in-between.  Conditional 
logic allows you to assign probabilities to statements.  A person can be in
the set with a certain probability.  The complications begin when you start
to apply operators like 'and' or 'or'.  In normal logic, this is easy 
(true 'and' true) = true.  In conditional logic, you might have multiple
probabilistic dependencies that have to be calculated in a reasonable manner.

If I recall right, the expert system Mycin used a simplistic method to apply
those operators.  If you had three statements with probabilities of
0.2,0.4, and
0.8, then the 'OR' of those three statements was simply the greatest
value (0.8)
and the 'AND' of those three statements was simply the lowest value (0.2).  

So, in order to give something that people can respond to (I'm really
curious about what fuzzy-logic really is), I make the following claim:

Fuzzy-logic is essentially conditional logic but with a well-defined
method (I don't know what it is) for applying operators (like 'and' or 'or')
to statements with multiple probabilistic dependencies.

Any comments?  (I hope so.)

-Vincent Huffaker

 e-mail = ah314368@longs.lance.colostate.edu

-------------------------------------------------------------------
No, I haven't made my .sig file yet and thanks so much for reminding me.