We obtain approximation ratio [Formula presented] for the (undirected) k-CONNECTED SUBGRAPH problem, where [Formula presented] is the largest integer such that 2ℓ−1k2ℓ+1≤n. For large values of n this improves the ratio 6 of Cheriyan and Végh  when n≥k3 (the case ℓ=1). Our result implies an fpt-approximation ratio 4+ϵ that matches (up to the “+ϵ” term) the best known ratio 4 for k=6,7 for both the general and the easier augmentation versions of the problem. Similar results are shown for the problem of covering an arbitrary symmetric crossing supermodular biset function.
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- Approximation algorithm
- Crossing supermodular functions
- k-connected subgraph