big and means e de or u is relatively big in a negative direction ns is negative small and means e de or u is relatively small in a negative direction ps is positive small and means e de or u is relatively small in a positive direction pb is positive big it means e de or u is relatively big in a positive direction the membership function is a graphic representation of the degree of membership of each input to a specific fuzzy subset the number of membership functions associated with an input equals the number of fuzzy subsets subdomains defined for that particular input fig3 a and 3b show a graphic representation of the five membership functions nb ns ze ps pb associated with each subdomain e and de the linguistic variable for the controller output is u the membership functions for the input fuzzy sets negative small ns zero ze positive small ps are triangular and the membership functions for negative big nb and positive big pb are half triangular with shoulders indicating the physical limits for the process the fuzzy controller 221 evaluates the inputs e and de using a set of rules corresponding to if a and b then c the part of the rule delimited by u201c if u201d is the antecedent of the rule and refers to the status of the inputs the part of the rule following u201c then u201d is the consequent and describes the status of.