def METHOD_NAME(bif_point, method='first'):
    """Calculate the diameter power relation at a bifurcation point.
    The diameter power relation is defined in https://www.ncbi.nlm.nih.gov/pubmed/18568015
    This quantity gives an indication of how far the branching is from
    the Rall ratio
    diameter_power_relation==1 means perfect Rall ratio
    """
    _raise_if_not_bifurcation(bif_point)
    if method not in {'first', 'mean'}:
        raise ValueError('Please provide a valid method for sibling ratio, found %s' % method)
    if method == 'first':
        # the first point is the same as the parent last point
        d_child = bif_point.points[-1, COLS.R]
        d_child1 = bif_point.children[0].points[1, COLS.R]
        d_child2 = bif_point.children[1].points[1, COLS.R]
    if method == 'mean':
        d_child = section_mean_radius(bif_point)
        d_child1 = section_mean_radius(bif_point.children[0])
        d_child2 = section_mean_radius(bif_point.children[1])
    return (d_child / d_child1)**(1.5) + (d_child / d_child2)**(1.5)