function f=f(t)
T=1/270833;
N=8;
dt=T/N;
t=[4*T:dt:10*T];                                        %顯示三個周期
f=zeros(1,length(t)); 
close all;
hold on
for i=1:50                                              %畫圖50次
b=sign(randn(1,2000));
  for n=1:length(t)
       k=floor(t(n)/T);                                 %下取整
       L=sum(b(1:k-3));
       %L=mod(sum(b(1:k-3)),4);                         %畫眼圖時取模可減少計算次數
       f1=pi*b(k-2)*quad(@g,-2.5*T,1.5*T+t(n)-k*T);     %對g（t）積分
       f2=pi*b(k-1)*quad(@g,-2.5*T,0.5*T+t(n)-k*T);
       f3=pi*b( k )*quad(@g,-2.5*T,-0.5*T+t(n)-k*T);
       f4=pi*b(k+1)*quad(@g,-2.5*T,-1.5*T+t(n)-k*T);
       f5=pi*b(k+2)*quad(@g,-2.5*T,-2.5*T+t(n)-k*T);
       f(n)=f1+f2+f3+f4+f5+L*pi/2;
  end
plot(t,cos(f));                                
end