How to obtain the fuzzy input membership grades for all MFs given an input value

Hi and Good Day all,

I need your help in the following:

When we evaluate a set of input, either using evalfis function or through the FIS Editor menu of View->Rules, how do we get the input's membership grades for each input membership functions that we have? Let say I have 3 input membership functions ie. Good, Moderate and Poor. So how do I get the grades for all of these 3 MF. The evalfis and View->Rules menu only display the output results. I also found out that I have the similar problem to get the grades of the input MF in the Interval Type-2 Fuzzy Toolbox.

I really hope to get some help from the group. Thank you very much in advance for your time and concern.

Answer 1

[Sam Chak]

Hi @mhilmi

Other than the evalfis() function, the evalmf() function can be used to obtain the membership function values.

%% initialize the FIS type
fis = mamfis;

%% add fuzzy variable
fis.Inputs(1) = fisvar([0 10], "Name", "Performance");

%% add fuzzy membership functions
fis.Inputs(1).MembershipFunctions(1) = fismf("linzmf", [2 5  ], "Name", "Poor");
fis.Inputs(1).MembershipFunctions(2) = fismf( "trimf", [2 5 8], "Name", "Moderate");
fis.Inputs(1).MembershipFunctions(3) = fismf("linsmf", [  5 8], "Name", "Good");

%% evaluate multiple MFs to get the membership function values
xinput = 6;
MFs_mu = evalmf(fis.Inputs(1).MembershipFunctions, xinput)

MFs_mu = 3×1

0 0.6667 0.3333

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%% plot results
figure
hold on
plotmf(fis, 'input', 1, 1001), ylim([-0.5, 1.5])
grid on, title('Input fuzzy sets')
plot(xinput, MFs_mu(2), 'ko')
plot(xinput, MFs_mu(3), 'ko')
hinput  = line([xinput xinput], [-0.2 1.0], 'Color', '#7F7F7F', 'LineStyle','--'); 
tinput  = text(xinput-0.5, -0.25,' input', 'FontWeight', 'bold');
hold off