Computes alpha and beta for periods when the benchmark return is negative.

    Parameters
    ----------
    see documentation for `alpha_beta`.

    Returns
    -------
    alpha : float
    beta : float

def down_alpha_beta(returns, factor_returns, **kwargs):
    """
    Computes alpha and beta for periods when the benchmark return is negative.

    Parameters
    ----------
    see documentation for `alpha_beta`.

    Returns
    -------
    alpha : float
    beta : float
    """
    return down(returns, factor_returns, function=alpha_beta_aligned, **kwargs)