On the Complexity of Sampling Redistricting Plans

A crucial task in the political redistricting problem is to sample redistricting plans i.e. a partitioning of the graph of census blocks into districts. We show that Recombination [DeFord-Duchin-Solomon’21]-a popular Markov chain to sample redistricting plans-is exponentially slow mixing on simple subgraph of ${\mathbb{Z}}_2\mathrm{.}$ We show an alternative way to sample balance, compact and contiguous redistricting plans using a “relaxed” version of ReCom and rejection sampling.