Approximation by lexicographically maximal solutions in matching and matroid intersection problems

• Published in: Theoretical computer science Vol. 910; pp. 48 - 53
• Main Authors: Bérczi, Kristóf, Király, Tamás, Yamaguchi, Yutaro, Yokoi, Yu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 02.04.2022
• Subjects: Approximation ratio; Lexicographical maximality; Matching; Matroid intersection; Matching; Lexicographical maximality; Matroid intersection; Approximation ratio
• ISSN: 0304-3975; 1879-2294
• DOI: 10.1016/j.tcs.2022.01.035

We study how good a lexicographically maximal solution is in the weighted matching and matroid intersection problems. A solution is lexicographically maximal if it takes as many heaviest elements as possible, and subject to this, it takes as many second heaviest elements as possible, and so on. If the distinct weight values are sufficiently dispersed, e.g., the minimum ratio of two distinct weight values is at least the ground set size, then the lexicographical maximality and the usual weighted optimality are equivalent. We show that the threshold of the ratio for this equivalence to hold is exactly 2. Furthermore, we prove that if the ratio is less than 2, say α, then a lexicographically maximal solution achieves (α/2)-approximation, and this bound is tight.