%P213 4
syms t
f1=sym('(1+t/2)*(Heaviside(t+2)-Heaviside(t))+(1-t/2)*(Heaviside(t)-Heaviside(t-2))');
f1_2=subs(f1,t,t-2);
f=f1_2*cos(10*t)
%求f1的傅立葉變換F1
R=0.02;t0=-4:R:4;
f1=subs(f1,t,t0);
W1=2*pi*5;
N=500;k=-N:N;W=k*W1/N;
F1=f1*exp(-j*t0'*W)*R;
F1w=abs(F1);
P1w=angle(F1);
figure(1)
subplot(3,1,1);plot(t0,f1);xlabel('t');ylabel('f(t)');title('f(t)=(1+t/2)*(Heaviside(t+2)-Heaviside(t))+(1-t/2)*(Heaviside(t)-Heaviside(t-2))');
subplot(3,1,2);plot(W,F1w);xlabel('w');ylabel('|F(w)|');
subplot(3,1,3),plot(W,P1w);xlabel('w');ylabel('|P(w)|');
%求f1(t-2)的傅立葉變換
R=0.02;t0=-4:R:4;
f1_2=subs(f1_2,t,t0);
W1=2*pi*5;
N=500;k=-N:N;W=k*W1/N;
F1_2=f1_2*exp(-j*t0'*W)*R;
F1_2w=abs(F1_2);
P1_2w=angle(F1_2);
figure(2)
subplot(3,1,1);plot(t0,f1_2);xlabel('t');ylabel('f(t)');title('f(t－2)');
subplot(3,1,2);plot(W,F1_2w);xlabel('w');ylabel('|F(w)|');
subplot(3,1,3),plot(W,P1_2w);xlabel('w');ylabel('|P(w)|');
%求f的傅立葉變換
R=0.02;t0=-4:R:4;
f=subs(f,t,t0);
W1=2*pi*5;
N=500;k=-N:N;W=k*W1/N;
F=f*exp(-j*t0'*W)*R;
Fw=abs(F);
Pw=angle(F);
figure(3)
subplot(3,1,1);plot(t0,f);xlabel('t');ylabel('f(t)');title('f(t－2)*cos(100t)');
subplot(3,1,2);plot(W,Fw);xlabel('w');ylabel('|F(w)|');
subplot(3,1,3),plot(W,Pw);xlabel('w');ylabel('|P(w)|');