A (Slightly) Improved Bound on the Integrality Gap of the Subtour LP for TSP
Anna R. Karlin, Nathan Klein, Shayan Oveis Gharan · 2022
In this extended abstract, we show that for some $\epsilon>10^{-36}$ and any metric TSP instance, the max entropy algorithm studied by [1] returns a solution of expected cost at most $\frac{3}{2}-\epsilon$ times the cost of the optimal solution to the subtour elimination LP. This implies that the integrality gap of the subtour LP is at most $\frac{3}{2}-\epsilon$. This analysis also shows that there is a randomized $\frac{3}{2}-\epsilon$ approximation for the 2-edge-connected multi-subgraph problem, improving upon Christofides’ algorithm.