Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!waikato.ac.nz!comp.vuw.ac.nz!cc-server4.massey.ac.nz!G.Moretti Newsgroups: comp.ai Subject: Re: What is "fuzzy logic"? Message-ID: <1991Apr2.225508.19059@massey.ac.nz> From: G.Moretti@massey.ac.nz (Giovanni Moretti) Date: Tue, 2 Apr 91 22:55:08 GMT References: <1991Mar28.192533.3272@waikato.ac.nz> <13842@ccncsu.ColoState.EDU> Organization: Massey University, Palmerston North, New Zealand Keywords: Fuzzy Logic, expert systems, bibliography X-Reader: NETNEWS/PC Version 2.2 Lines: 101 The easiest way I've found to think about fuzzy logic as related to expert systems, is that you have rules with conditions and results in the usual way, except that the conditions may have a modifier attached to them so they're not BOOLEAN (ie TRUE or FALSE) but have some degree of being TRUE or applicable. How well the conditions are fulfilled affects how much significance is given to the conclusion. So, instead of the usual rules: 1) if HEATSINK_TEMP > HOT and AMBIENT_TEMPERATURE = HOT then FAN:= ON 2) if HEATSINK_TEMP < HOT Then FAN:= OFF where Heatsink_temp is an integer and hot = 55 we could have in a fuzzy system 3) if HEATSINK_TEMP is HOT then INCREASE power_to_fan 4) if HEATSINK_TEMP is COLD then DECREASE power_to_fan where Heatsink temperature is one of COLD, COOL, MODERATE, WARM and HOT THIS is CRUCIAL *********************************************************************** * ALL OF THE RULES AND THEIR CONCLUSIONS ARE EVALUATED EVERY TIME * *********************************************************************** This means that: -rule 3's conclusion will be evaluated even if the temperature is COLD but the value of the increase will be very small. However as the temperature increases, the increase in fan power from rule 3 starts to dominate as the value of HEATSINK_TEMP approaches HOT (the gradations of TEMPERATURE may be COLD, COOL, MODERATE, WARM and HOT). The value of INCREASE or DECREASE are related to how closely the conditions are met. This would give much smoother control of the temperature with only two rules than the brute force FULL-ON or FULL-OFF approach. *** This evaluation of all of the rules all of the time means that the system can easily handle conflicting rules and inputs. *** The significance given to the conclusion is related to how well the conditions are met, meaning that fewer rules are necessary. There you have it - my understanding in a nutshell ... I just wish it didn't sound so authoritative :-) For more info: REFERENCES: Here's some of the articles I've found relating to Fuzzy Logic, listed in order of ease of comprehension for a newcomer. "Designing with Fuzzy Logic", Kevin Self, IEEE Spectrum, Nov 1990 p42 .. Easy to read introduction - START HERE. "Knowledge Representation in Fuzzy Logic" by Lofti Zaheh. IEEE Transactions on Knowledge and Data Engineering, Vo1 No1 March 1989, p89. This is a good article to go back to after you've read the one above as it describes Knowledge Representation in fuzzy logic but not particularly in terms of expert systems. "Implementing Fuzzy Rule-Based Systems on Silicon Chips" by Men-Hiot Lim and Yoshiyasu Takifuji. IEEE Expert, February 1990, p31 Building a chip to perform fuzzy inferencing using an example of determining whether or not to grant a loan based on several financial criteria. Takes some thinking about but covers a lot of ground and does it quite well. "Parallel Rule-based Fuzzy Inference on Mesh-connected Systolic Arrays" by M.A. Eshera and S.C.Barash. IEEE Expert, Winter 1989 (Vol 4 no 4), p27... I don't even understand the title and haven't tried to digest the article. It's heavily into parallel processing, as you might expect from the title :-). Cheers Giovanni -- ------------------------------------------------------------------------------ Giovanni Moretti, Consultant | G.Moretti@massey.ac.nz, Pkt-ZL2BOI@ZL2TCX Computer Centre, Massey University| Ph 64 63 69099 x8398, FAX 64 63 505607 Palmerston North, New Zealand | QUITTERS NEVER WIN, WINNERS NEVER QUIT ------------------------------------------------------------------------------