Double for loop problem. Function within 2nd for loop no longer works properly.

I'm trying to create graphs of 8 Fourier transform calcultations. When I input the nmax value manually, my function works correctly, but as I'd like to graph all 8 results simultanneously, i've created another for loop. However, this is changing the function output and I don't understand why. nmax(i) has the correct value becuase it's displayed in the graph subtitle correctly, yet the function does not output the same graph as when I input the values for nmax manually.

It must be an issue with the structure of my for loops. I'm new to MATLAB. Any help apprecitated, thank you :)

clear, clc, clf;

nmax = [1, 3, 5, 10, 20, 50, 100, 200];

t = 0:0.01:20;

T = 5;

A = 2;

a0 = A/2;

wo = 2*pi/T;

Q = ones(1,length(t));

FS = a0*Q;

for i = 1:length(nmax)

for n = 1:nmax(i)

an = A / (pi*n) * sin(pi*n);

bn = A * (1- cos(pi*n)) / (pi*n);

FS = FS + an*cos(n*wo*t) + bn*sin(n*wo*t);

end

subplot(length(nmax)/2,2,i);

plot(FS);

title('Trigonometric Fourier Series Sum');

txt=['nMax = ', num2str(nmax(i))];

subtitle(txt);

xlabel('Time');

ylabel('Amplitude');

ylim ([-5 20]);

end

Answer 1

[Voss]

Move this line:

FS = a0*Q;

into your outer for loop (but still outside the inner loop). This will re-initialize FS each time through the outer loop, which is necessary because otherwise the result is accumulated with the previously calculated FS values.

[Ben Robson]

That's it! Thanks for your help.