__
TR21-121 | 21st August 2021 11:16
__

#### Matroid Intersection: A pseudo-deterministic parallel reduction from search to weighted-decision

**Abstract:**
We study the matroid intersection problem from the parallel complexity perspective. Given

two matroids over the same ground set, the problem asks to decide whether they have a common base and its search version asks to find a common base, if one exists. Another widely studied variant is the weighted decision version where with the two matroids, we are given small weights on the ground set elements and a target weight W, and the question is to decide whether there is a common base of weight at least W. From the perspective of parallel complexity, the relation between the search and the decision versions is not well understood. We make a significant progress on this question by giving a pseudo-deterministic parallel (NC) algorithm for the search version that uses an oracle access to the weighted decision.

The notion of pseudo-deterministic NC was recently introduced by Goldwasser and Grossman [GG17], which is a relaxation of NC. A pseudo-deterministic NC algorithm for a search problem is a randomized NC algorithm that, for a given input, outputs a fixed solution with high probability. In case the given matroids are linearly representable, our result implies a pseudo-deterministic NC algorithm (without the weighted decision oracle). This resolves an open

question posed by Anari and Vazirani [AV20].