def stan_init(m):
    """Retrieve parameters from a trained model.

    Retrieve parameters from a trained model in the format
    used to initialize a new Stan model.

    Parameters
    ----------
    m: A trained model of the Prophet class.

    Returns
    -------
    A Dictionary containing retrieved parameters of m.

    """
    res = {}
    for pname in ['k', 'm', 'sigma_obs']:
        res[pname] = m.params[pname][0][0]
    for pname in ['delta', 'beta']:
        res[pname] = m.params[pname][0]
    print(f'Trained model: {res}')
    return res