function[t st]=lpf(f,sf,B)
%This function filter an input data using a lowpass filter
%inputs:f:frequency samples
% sf:input data spectrum samples
%B:lowpass's bandwidth with a rectangle lowpass
%Outpus:t;time samples
%st:output data's times samples
df=f(2)-f(1);
T=1/df;
hf=zeros(1,length(f));
bf=[-floor(B/df):floor(B/df)]+floor(length(f)/2);
hf(bf)=1;
yf=hf.*sf;
[t,st]=F2T(f,yf);
st=real(st);