def starting_guess(mini, estimate_sigma=True):
    """
    Use best a fit as a starting point for the samplers.
    If no sigmas are given, it is assumed that
    all points have the same uncertainty which will
    be also part of the sampled parameters.
    """
    vals = [i.value for i in mini.params.values() if i.vary]
    if estimate_sigma:
        vals.append(mini.residual.std())
    return vals