def comp_radius_mid_active(self):
    """Compute the radius at the middle of the active part of the slot

    Parameters
    ----------
    self : Slot
        A Slot object

    Returns
    -------
    Rmw: float
        Mid active radius [m]

    """

    Rbo = self.get_Rbo()
    Hslot = self.comp_height()
    Hwind = self.comp_height_active()
    if self.is_outwards():
        return Rbo + Hslot - Hwind / 2
    else:
        return Rbo - Hslot + Hwind / 2