# How to define Fuzzy Rules?

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Moussa on 31 Jan 2024
Answered: Sam Chak on 31 Jan 2024
I have an assignment related to fuzzy logic. In the following part of the assignment, I have come to a halt. There are 4 inputs and 1 output, and each of them has 3 membership functions. I am required to generate 81 rules from these components. However, as you can observe from the attached image, the total number of rules is 3^5=243. I am unsure of how to select the specific 81 rules from this larger set.

Sam Chak on 31 Jan 2024
Hello @Moussa
Here's how we go about estimating the number of rules based on the given number of inputs and the number of membership functions (MFs) for each input. Ideally, you'd also want to generate 81 MFs for the output. Nevertheless, there's flexibility to reuse certain MFs for specific rules, depending on the situation as perceived by the human designer.
nInput = 4; % number of Inputs
nMFcns = 3; % number of MFs
nRules = nMFcns^nInput % number of Rules
nRules = 81