Initial conditions and refinement regions. The black, blue, violet, green, yellow, and red curves show the isodensity contours that contain 90%, 80%, 70%, 60%, 50%, and 40% of the disc mass at t = 0, respectively. The black, blue, violet, green, yellow, and red dashed lines show the cylinders within which the cell size equals 1/8, 1/16, 1/32, 1/64, 1/128, and 1/256 of the disc exponential scale length, respectively.