def from_string(psd_name, length, delta_f, low_freq_cutoff):
    """Generate a frequency series containing a LALSimulation PSD specified
    by name.

    Parameters
    ----------
    psd_name : string
        PSD name as found in LALSimulation, minus the SimNoisePSD prefix.
    length : int
        Length of the frequency series in samples.
    delta_f : float
        Frequency resolution of the frequency series.
    low_freq_cutoff : float
        Frequencies below this value are set to zero.

    Returns
    -------
    psd : FrequencySeries
        The generated frequency series.
    """

    # check if valid PSD model
    if psd_name not in get_psd_model_list():
        raise ValueError(psd_name + ' not found among analytical '
                         'PSD functions.')

    # if PSD model is in LALSimulation
    if psd_name in get_lalsim_psd_list():
        lalseries = lal.CreateREAL8FrequencySeries(
            '', lal.LIGOTimeGPS(0), 0, delta_f, lal.DimensionlessUnit, length)
        try:
            func = lalsimulation.__dict__[
                                        _name_prefix + psd_name + _name_suffix]
        except KeyError:
            func = lalsimulation.__dict__[_name_prefix + psd_name]
            func(lalseries, low_freq_cutoff)
        else:
            lalsimulation.SimNoisePSD(lalseries, 0, func)
        psd = FrequencySeries(lalseries.data.data, delta_f=delta_f)

    # if PSD model is coded in PyCBC
    else:
        func = pycbc_analytical_psds[psd_name]
        psd = func(length, delta_f, low_freq_cutoff)

    # zero-out content below low-frequency cutoff
    kmin = int(low_freq_cutoff / delta_f)
    psd.data[:kmin] = 0

    return psd
Generate a frequency series containing a LALSimulation PSD specified
    by name.

    Parameters
    ----------
    psd_name : string
        PSD name as found in LALSimulation, minus the SimNoisePSD prefix.
    length : int
        Length of the frequency series in samples.
    delta_f : float
        Frequency resolution of the frequency series.
    low_freq_cutoff : float
        Frequencies below this value are set to zero.

    Returns
    -------
    psd : FrequencySeries
        The generated frequency series.