%% this function plots the fft of and input x
function showfft(data)
figure
ld=length(data);
f=0:1/ld:1-1/ld;
df=abs(fft(data));
df=df/max(df);
semilogy(f,df)
axis([0:1, 0.001 1.1])
xlabel('f/f_s');
ylabel('Spectrum of data')