fouri1.m

傅立叶变换源程序

clear;
t=0:0.001:1;
tdata=square(2*pi*15*t);
subplot(5,1,1);
plot(t,tdata);
axis([0 0.5 -2 2]);
N = length(tdata);
fs = 1 / (t(2) - t(1));
df = fs / N;
f = [0:df:df * (N - 1)] - fs / 2;
fdata = fft(tdata);
fdata = fftshift(fdata / fs);

subplot(5,1,2);
plot(t,tdata);
axis([0 0.5 -2 2]);
xlabel('时间');
ylabel('信号');

subplot(5,1,3);
plot(f,abs(fdata));
xlabel('频率');
ylabel('幅度');
title('傅立叶正变换')
N = length(fdata);
ts = 1 / (f(2) - f(1));
dt = ts / N;
t = [0 : dt : dt * (N - 1)];
tdata = ifft(ifftshift(fdata));
tdata = tdata / dt;
subplot(5,1,4);
plot(f,abs(fdata));
xlabel('频率');
ylabel('幅度');

subplot(5,1,5);
plot(t,abs(tdata) .* sign( angle(tdata)));
xlabel('时间');
ylabel('幅度');
title('傅立叶反变换')
axis([0 0.5 -2 2]);