Power-law fits to the correlations between the 2–10 keV Swift/XRT X-ray flux and the interpolated g′-band flux density of MAXI J1820+070. (a): Joint fit to the initial rise of HS1 and the final decay of HS2, and a separate fit to the IMS and SS phases. (b): Joint fit to the rise phases of mini-outbursts 1 and 2. (c): Joint fit to the initial rise of HS1, the final decay of HS2, and the decay phases of mini-outbursts 1, 2, and 3. Note: The upper-limit points are not included in the fitting of (c).