Surface density and eccentricity evolution for the circumbinary disk. Here e_d represents the mass-averaged particle eccentricity magnitude and is used as a statistical measure of orbital noncircularity. From top to bottom, the rows show the results for models with (e_b = 0,  q = 1.92), (e_b = 0.2,  q = 1.92), (e_b = 0.4,  q = 1.92), (e_b = 0,  q = 1.00), and (e_b = 0,  q = 0.52), respectively (runs 5–9).