Yi Wu IBM Almaden Research Joint work with Alina Ene and Jan Vondrak
Definition of Problems
Graph Multiway Cut
Goal: remove minimum number of edges to disconnect the terminals.
Graph Multiway Cut
1 2 3
Approximability of Graph Multiway Cut
Variant: Node Weighted Multiway Cut Goal: remove minimum number (weights) of nodes to disconnect the terminals.
Variant: Hypergraph Multiway Cut (HMC)
Generalization: Submodular Multiway Partition
Another interesting SMP: Hypergraph Multiway Partition
Relationship Submodular Multiway Partition Hypergraph Multiway cut = Node Weighted Multiway Cut Hypergraph Multiway Partition. Graph Multiway Cut
Our Results
Our Results (1) 4/3-approximation for 3- way submodular partion. Based on the half integrality of an LP.
Overview of the algorithm
The rounding algorithm
Our result (2) matching UG-hardness
The LP for Hypergraph Multiway Cut
The LP for general Min-CSP
Our Results (3): matching oracle hardness Q: is it a coincident that the oracle hardness is the same as the Unique Games hardness? Q: is it a coincident that the oracle hardness is the same as the Unique Games hardness?
Symmetric gap for Hypergraph Multiway Cut Optimum Symmetric solution (by independent rounding). Optimum solution (by independent rounding).
Why study symmetric gap?
Our Results (4) Q: is it a coincident that the oracle hardness is the same as the Unique Games hardness? A: No. We prove that for any CSP instance, symmetric gap = LP integrality gap.
Conclusion
Open problem