fouriertransform with piecewise function

Question

Elisa 2022-12-11

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1876037-fouriertransform-with-piecewise-function

编辑： Paul 2022-12-13

I am trying to apply a fft (fourier transform) into a piecewise function, but i receive the following message: "Error using fft

Invalid data type. First argument must be double, single, int8, uint8, int16, uint16, int32, uint32, or logical."

Code:

figure(1);
syms t
x = piecewise(-1/2<=t<=1/2, 1-abs(t), t<-1/2, 0 , t>1/2, 0);
fplot(x,[-2,2])
grid
xlabel("Time")
ylabel("Amplitude")
fa = 15000; 
t = 0:1/fa:2; 
y=fft(x);
f = -fa:1:fa;
figure(2);
subplot(2,1,1);
plot(f,abs(y_ajustado)/fa);
xlabel("Frequency (Hz)")
ylabel("Amplitude")
xlim([0 400]) 
subplot(2,1,2)
plot(f,angle(y_ajustado));
xlabel("Frequency (Hz)")
ylabel("Fase (Graus)")
xlim([0 400])

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Answer 1

VBBV 2022-12-11

1
链接

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https://ww2.mathworks.cn/matlabcentral/answers/1876037-fouriertransform-with-piecewise-function#answer_1125732

在 MATLAB Online 中打开

use double and subs() the result of x

figure(1);

syms t

x = piecewise(-1/2<=t<=1/2, 1-abs(t), t<-1/2, 0 , t>1/2, 0)

x =

fplot(x,[-2,2])

grid

xlabel("Time")

ylabel("Amplitude")

fa = 15000;

t = 0:1/fa:2;

y=fft(double(subs(x,t)));

plot(t,real(y),t,imag(y))

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Elisa 2022-12-12

thank you!!!!

Paul 2022-12-12

编辑：Paul 2022-12-13

Why is y plotted agains t? Shouldn't y be plotted against frequency? And the fft is only taken for the portion of the signal for t>=0, but it's non-zero for t < 0.

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