function[t,st]=bpf(f,sf,B1,B2)
df=f(2)-f(1);
T=1/df;
hf=zeros(1,length(f));
bf=[floor(B1/df):floor(B2/df)];
bf1=floor(length(f)/2)+bf;
bf2=floor(length(f)/2)-bf;
hf(bf1)=1/sqrt(2*(B2-B1));
hf(bf2)=1/sqrt(2*(B2-B1));



yf=hf.*sf.*exp(-j*2*pi*f*0.1*T);
[t,st]=F2T(f,yf);

这个程序是一个带通滤波器
f: frequency samples
sf:input data spectrum samples
B1: bandpass's lower frequency
B2:bandpass's higher frequency
t:time samples
st:output data's time samples