Online minimum matching with uniform metric and random arrivals

We consider Online Minimum Bipartite Matching under the uniform metric. We show that Randomized Greedy achieves a competitive ratio equal to $(1+1/n) (H_{n+1}-1)$, which matches the lower bound. Comparing with the fact that RG achieves an optimal ratio of $\mathrm{\Theta }(\ln n)$ for the same problem but under the adversarial order, we find that the weaker arrival assumption of random order doesn’t offer any extra algorithmic advantage for RG, or make the model strictly more tractable.