def to_sir(scale, decay, n):
    """
    Return the parameters of the equivalent SIR model.

    Parameters
    ----------
    scale : float
        See the corresponding parameters in :meth:`exp_intensity` for more
        information.
    decay : float
        See the corresponding parameters in :meth:`exp_intensity` for more
        information.
    n : int
        See the corresponding parameters in :meth:`exp_intensity` for more
        information.

    Returns
    -------
    sir_parameters : dict
        Dictionary containing the corresponding SIR parameters n, i_0, beta
        (infection rate), and gamma (recovery rate).

    Examples
    --------
    >>> obtained = HawkesN.to_sir(scale=5, decay=0.2, n=400)
    >>> desired = {"n": 400, "i_0": 1, "beta": 1.0, "gamma": 0.2}
    >>> obtained == desired
    True
    """
    i_0 = 1  # the HawkesN process is assumed to have 1 "immigrant" at t=0
    beta = scale * decay
    gamma = decay
    return {"n": n, "i_0": i_0, "beta": beta, "gamma": gamma}