def sn_ratio(signal_power, noise_power,
             output=None,
             verbose=0):
    """
    Returns the signal-to-noise ratio.

    Parameters
    ----------
    signal_power : power of signal [eV^2]
    noise_power : power of noise [eV^2]
    output : output dictionary (default: None)
    verbose : verbosity (default: 0)
    """

    # ratio
    res = signal_power / noise_power

    if type(output) == dict:

        # saving to ouput dictionary
        output['S/N_power'] = res

        if verbose > 0:
            print("S/N computed and saved in output['S/N_power'].")

    return res