What is fuzzy logic?

Question

I'm working with a couple of AI algorithms at school and I find people use the words Fuzzy Logic to explain any situation that they can solve with a couple of cases. When I go back to the books I just read about how instead of a state going from On to Off it's a diagonal line and something can be in both states but in different "levels".

I've read the wikipedia entry and a couple of tutorials and even programmed stuff that "uses fuzzy logic" (an edge detector and a 1-wheel self-controlled robot) and still I find it very confusing going from Theory to Code... for you, in the less complicated definition, what is fuzzy logic?

Answer 1

Fuzzy logic is logic where state membership is, essentially, a float with range 0..1 instead of an int 0 or 1. The mileage you get out of it is that things like, for example, the changes you make in a control system are somewhat naturally more fine-tuned than what you'd get with naive binary logic.

An example might be logic that throttles back system activity based on active TCP connections. Say you define "a little bit too many" TCP connections on your machine as 1000 and "a lot too many" as 2000. At any given time, your system has a "too many TCP connections" state from 0 (<= 1000) to 1 (>= 2000), which you can use as a coefficient in applying whatever throttling mechanisms you have available. This is much more forgiving and responsive to system behavior than naive binary logic that only knows how to determine "too many", and throttle completely, or "not too many", and not throttle at all.

Answer 2

I'd like to add to the answers (that have been modded up) that, a good way to visualize fuzzy logic is follows:

Traditionally, with binary logic you would have a graph whose membership function is true or false whereas in a fuzzy logic system, the membership function is not.

 1|  |   /\  |  /  \  | /    \ 0|/      \  ------------    a  b c   d 

Assume for a second that the function is "likes peanuts"

 a. kinda likes peanuts b. really likes peanuts c. kinda likes peanuts d. doesn't like peanuts 

The function itself doesn't have to be triangular and often isn't (it's just easier with ascii art).

A fuzzy system will likely have many of these, some even overlapping (even opposites) like so:

 1|   A    B  |   /\  /\      A = Likes Peanuts  |  /  \/  \     B = Doesn't Like Peanuts  | /   /\   \ 0|/   /  \   \  ------------   a  b  c d 

so now c is "kind likes peanuts, kinda doesn't like peanuts" and d is "really doesn't like peanuts"

And you can program accordingly based on that info.

Hope this helps for the visual learners out there.