dm10403.m

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

% dm10403
% 傅里叶变换的时移特性
display('please input the value of t0(0<t0<0.4)');
t0 = input('t0 = ');                                           %输入时移量
dt = 0.02;
t = -5:dt:5;
N = 300;
W = 5*pi*2;                                                   %采样角频率
k = -N:N;
w = k*W/N;
%定义f1(t)=1/2*exp(-2*t)*u(t)
f1 = 1/2*exp(-2*t).*Heaviside(t);  
F1 = dt*f1*exp(-j*t'*w);                                     %求f1(t)的傅里叶变换F1(ω)
F1m = abs(F1);                                               %求F1(ω)的幅度频谱
P1a = angle(F1);                                             % 求F1(ω)的相位频谱
%定义f2(t)=1/2*exp(-2*(t-t0))*u(t-t0)
f2 = 1/2*exp(-2*(t-t0)).*Heaviside(t-t0);   
F2 = dt*f2*exp(-j*t'*w);                                     %求f2(t)的傅里叶变换F2(ω)
F2m = abs(F2);                                               %求F2(ω)的幅度频谱
P2a = angle(F2);                                             %求F2(ω)的相位频谱
%定义f3(t)=1/2*exp(-2*(t+t0))*u(t+t0)
f3 = 1/2*exp(-2*(t+t0)).*Heaviside(t+t0);  
F3 = dt*f3*exp(-j*t'*w);                                    %求f3(t)的傅里叶变换F3(ω)
F3m = abs(F3);                                              %求F3(ω)的幅度频谱
P3a = angle(F3);                                            %求F3(ω)的相位频谱
%绘制图形
subplot(311);
h1 = plot(t,f1,'r');                                       %用红色实心线绘制f1(t)
xlabel('t');
ylabel('f(t)');
hold on 
h2 = plot(t,f2,'b:');                                      %用蓝色虚线绘制f2(t)
h3 = plot(t,f3,'g-.');                                     %用绿色点画线绘制f3(t)
axis([-6 6 0 0.6]);
legend('f1(t)','f2(t)','f3(t)');
subplot(312);
plot(w,F1m,'r');
xlabel('w');
ylabel('F(jw)');
hold on 
plot(w,F2m,'b:');
plot(w,F3m,'g-.');
axis([-6 6 0 0.3]);
subplot(313);
plot(w,P1a*180/pi,'r');
xlabel('w');
ylabel('P(度)');
hold on
plot(w,P2a*180/pi,'b:');
plot(w,P3a*180/pi,'g-.');
axis([-6 6 -200 200]);
%End