using DSP

"""
    tfest(y,u)

Estimate a transfer function model using the Correlogram approach
H = Syu/Suu
"""
function tfest(y,u)
    Cyu = xcorr(y,u)
    Cuu = xcorr(u,u)
    Syu = welch_pgram(Cyu)
    Suu = welch_pgram(Cuu)
    return H = TFdata(Syu.power./Suu.power,Syu.freq)
end

tfest(iddata::IdData) = tfest(iddata.y,iddata.u)