Characterization of the split closure via geometric lifting

• We analyze split cuts from the perspective of cut generating functions.
• We show that k-cuts give all the split cuts for the mixed-integer corner relaxation.
• This implies that all splits are restrictions of splits for the infinite relaxation.
• We construct pure-integer IPs with arbitrarily bad split closure.

We analyze split cuts from the perspective of cut generating functions via geometric lifting. We show that α-cuts, a natural higher-dimensional generalization of the k-cuts of Cornuéjols et al., give all the split cuts for the mixed-integer corner relaxation. As an immediate consequence we obtain that the k-cuts are equivalent to split cuts for the 1-row mixed-integer relaxation. Further, we show that split cuts for finite-dimensional corner relaxations are restrictions of split cuts for the infinite-dimensional relaxation. In a final application of this equivalence, we exhibit a family of pure-integer programs whose split closure has arbitrarily bad integrality gap. This complements the mixed-integer example provided by Basu et al. (2011).