Why dosent my fourier output simulate the input?

Question

Jamie Chambers 2017-2-18

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/325750-why-dosent-my-fourier-output-simulate-the-input

评论： Jamie Chambers 2017-2-20

This is my input signal:

clc
clear all 
syms L psi f(x) t 
L=2*pi;
psi=pi;
f(x)=(t-psi)^2; 
ezplot(f(x),[0,2*pi])
xlabel ('period 0,2*pi')
ylabel ('amplitude')
title ('input signal')
pretty(f(x))

I'm trying to plot the Fourier using this code:

clc
clear all 
syms n m L t psi x 
L=2*pi;
psi=pi
f(x)=(t-psi)^2 
A0=int(f(x),t,0,2*pi)/L
ezplot(A0,[0,2*pi])
hold on 
for m=1:10
    An=int(f(x)*cos(n*t),t,0,L)*(L/1);
    An=subs(An,n,m);
    Bn=int(f(x)*sin(n*t),t,0,L)*(L/1);
    Bn=subs(Bn,n,m);
    Fo=A0+sum((An*cos(n*pi)/L)*f(x)+(Bn*sin(n*pi)/L)*f(x))
    Fo=subs(Fo,n,m);
    ezplot(Fo,[0,2*pi])
    ylim auto 
    hold on
end

I've tried numerous attempts but cant seen to generate the simulated input???? what a I doing wrong? Regards J

1 个评论
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John BG 2017-2-18

do you have the symbolic toolbox?

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Answer 1

Frank Macias-Escriva 2017-2-19

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/325750-why-dosent-my-fourier-output-simulate-the-input#answer_255407

在 MATLAB Online 中打开

Try this code bellow:

syms t n; 
L = 2*pi;
f(t) = (t-pi)^2;
figure('Name', 'Original signal');
ezplot(f(t), [0, L]);
ylim auto;
N = 100;
A0 = int(f(t), t, 0, L)/L;
A(n) = int(f(t)*cos(n*t), t, 0, L) * (2/L);
B(n) = int(f(t)*sin(n*t), t, 0, L) * (2/L);
Fo(t) = A0 + symsum(A(n)*cos(n*t) + B(n)*sin(n*t), n, 1, N);
figure('Name', 'Generated signal');
ezplot(Fo(t), [0, L]);
ylim auto;

In this code, you avoid using for loops and keep using the symbolic toolbox for the entire solution. Also, note te use of "symsum" instead of "sum". Play with N for getting different accuracies of the generated signal.

Best,

fm