dm10405.m

the code of the book come form the book of marlix laboratory with the book of singal

% dm10405
% 傅里叶变换的时域卷积定理
dt = 0.005;
t = -2:dt:2;
f = Heaviside(t+1)-Heaviside(t-1);          %脉宽为2的门信号
subplot(221);
plot(t,f)
xlabel('t');
title('f(t)');
axis([-2 2 -0 1.1]);
y = dt*conv(f,f);                            %求卷积
n = -4:dt:4;                                 %y取值范围为f取值范围的两倍(-4~+4)
subplot(222);
plot(n,y);
xlabel('t');
title('y(t)=f(t)*f(t)');
axis([-4 4 -0 2.1]);
W1 = 2*pi*5;
N = 200;
k = -N:N;
W = k*W1/N;
F = f*exp(-j*t'*W)*dt;  %求f(t)的傅里叶变换F(ω)
F = abs(F);               %求f(t)幅度频谱          
Y = y*exp(-j*n'*W)*dt;  %求y(t)的傅里叶变换Y(ω)
Y = abs(Y);                %求y(t)幅度频谱
F1 = F.*F;  %求F(ω)×F(ω) 
subplot(223);
plot(W,F);
xlabel('w');
title('F(w)的幅度频谱');
subplot(224);
plot(W,F1);
xlabel('w');
title('Y(w)= F(w)×F(w)的幅度频谱');
axis([-20 20 0 4.1]);
axis([-20 20 0 4.1]);
%En