How to plot 3 membership function and find the µ of each one for a specific X ?

Hello ,

i want to plot 3 trapezoidal membership functions : the first one is : [ 0 0.3 0.4] second [0.3 0.4 0.6 0.7] third [0.6 0.7 1 ] like this

and i have a table of points that i want to plot here and get the membership function of each one i found how to do it with one function but not with 3 .

thank you for the help .

Answer 1

[Sam Chak]

Hi @redha wassim brahimi

You can refer to doc trapmf, and plot the membership functions.

Edit: To include the firing of fuzzy membership value μ corresponding to the x value,

x = 0:0.01:1;
y1 = trapmf(x, [-0.1 0.0 0.3 0.4]);
y2 = trapmf(x, [0.3 0.4 0.6 0.7]);
y3 = trapmf(x, [0.6 0.7 1.0 1.1]);
plot(x, y1, x, y2, x, y3, 'linewidth', 1.5)
hold on

xMark  = 0.67;
y1Mark = trapmf(xMark, [-0.1 0.0 0.3 0.4]);
y2Mark = trapmf(xMark, [0.3 0.4 0.6 0.7]);
y3Mark = trapmf(xMark, [0.6 0.7 1.0 1.1]);

plot(xMark*x, y2Mark*ones(size(x)), '--', 'linewidth', 1.25)
plot(xMark*x, y3Mark*ones(size(x)), '--', 'linewidth', 1.25)
plot(xMark*ones(size(x)), y3Mark*x, '--', 'linewidth', 1.25)
hold off

grid on
ylim([-0.2 1.4])
xlabel('x')
ylabel('Degree of Membership, \mu')
legend('faible', 'moyenne', 'forte', 'location', 'best')

[redha wassim brahimi]

thank you very much , i have seen the doc , i didn't know i can plot 3 graphs in 1 .

now i can do what i wanteds to but can i ask you another question ?

now i have for exemple the value 0.67 , i know i can get the values of the member ship function with

y1 = trapmf(0.67, [-0.1 0.0 0.3 0.4]);

y2 = trapmf(0.67, [0.3 0.4 0.6 0.7]);

y3 = trapmf(0.67, [0.6 0.7 1.0 1.1]);

but i want to plot it in the graph you showed me : exemple :

thank you again

[Sam Chak]

You are welcome, @redha wassim brahimi. In fact, you can refer the yline and xline to draw the horizontal line with constant y-value and the vertical line with constant x-value, respectively. Please consider Accept-clicking ✓ the Answer if your question is resolved.

[redha wassim brahimi]

thank you accepted !

[Sam Chak]

Hi @redha wassim brahimi

Thanks for your acceptance. I have edited the original Answer to include the firing of fuzzy membership value μ corresponding to the x value. I think you will like this, because you have more control over the plot.