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Abstract

The optimal $k$-restricted 2-factor problem consists of finding, in a complete undirected graph $K_n$, a minimum cost 2-factor (subgraph having degree 2 at every node) with all components having more than $k$ nodes. The problem is a relaxation of the well-known symmetric travelling salesman problem, and is equivalent to it when $\frac{n}{2}\leq k\leq n-1$. We study the $k$-restricted 2-factor polytope. We present a large class of valid inequalities, called bipartition inequalities, and describe some of their properties; some of these results are new even for the travelling salesman polytope. For the case $k=3$, the triangle-free 2-factor polytope, we derive a necessary and sufficient condition for such inequalities to be facet inducing.