def METHOD_NAME(array, time_step):
    """
    PSD function (Power Spectral Density) by Niels
    """
    f_axis = np.fft.fftfreq(len(array), time_step)
    idx = np.argsort(f_axis)
    f_axis = f_axis[idx]
    period = time_step*len(array)
    psd = time_step*time_step/period*(np.abs(np.fft.fft(array)))**2
    psd = psd[idx]
    return f_axis[len(psd)//2:], psd[len(psd)//2:]