def _scaling_func_list(bdry_fracs, exponent):
    """Return a list of lists of scaling functions for the boundary."""
    def scaling(factor):
        def scaling_func(x):
            return x * factor
        return scaling_func

    func_list = []
    for frac_l, frac_r in bdry_fracs:
        func_list_entry = []
        if np.isclose(frac_l, 1.0):
            func_list_entry.append(None)
        else:
            func_list_entry.append(scaling(frac_l ** (1 / exponent)))

        if np.isclose(frac_r, 1.0):
            func_list_entry.append(None)
        else:
            func_list_entry.append(scaling(frac_r ** (1 / exponent)))

        func_list.append(func_list_entry)
    return func_list
Return a list of lists of scaling functions for the boundary.