The syntax to add output membership functions is incorrect. Use 'addMF()' instead. However, it is highly recommended to use the Fuzzy Logic Designer app with interactive user interface.
% Create a sample FIS
fis = mamfis('Name',"tipper");
fis = addInput(fis,'NumMFs',3,'MFType',"gaussmf");
% Create Fuzzy Input #1
fis.Inputs(1).Name = "service";
fis.Inputs(1).Range = [0 10];
% Create Fuzzy Input #2
fis.Inputs(2).Name = "food";
fis.Inputs(2).Range = [0 10];
% Create Fuzzy Output #1
fis.Outputs(1).Name = "tip";
fis.Outputs(1).Range = [0 30];
% Add output membership functions
fis = addMF(fis, 'tip', 'zmf', [ 0 15], 'Name', 'low');
fis = addMF(fis, 'tip', 'zmf', [10 20], 'Name', 'medium');
fis = addMF(fis, 'tip', 'zmf', [15 25], 'Name', 'high');
fis = addMF(fis, 'tip', 'zmf', [20 30], 'Name', 'very_high');
plotmf(fis, 'output', 1), grid on, title('Tip')
% % Add rules
% rules = [...
% "If service is poor and food is rancid, then tip is cheap"; ...
% "If service is good and food is delicious, then tip is generous"; ...
% "If service is excellent and food is amazing, then tip is very generous"; ...
% "If service is poor and food is delicious, then tip is average"; ...
% "If service is good and food is rancid, then tip is little"; ...
% ];
% fis = addRule(fis, rules);
%
% % Perform rule pruning
% [pruned_fis, pruned_rules, pruned_outputs] = pruneRules(fis, 0.2);
%
% % Get remaining rules
% remaining_rules = getRuleValues(pruned_fis);
