Abstract
We present almost linear time approximation schemes for several generalized matching problems on nonbipartite graphs. Our results include \(O_\epsilon (m\alpha (m, n))\)-time algorithms for \((1-\epsilon )\)-maximum weight f-matching and \((1+\epsilon )\)-approximate minimum weight f-edge cover. As a byproduct, we also obtain direct algorithms for the exact cardinality versions of these problems running in \(O(m\alpha (m, n)\sqrt{f(V)})\) time, where f(V) is the sum of degree constraint on the entire vertex set. The technical contributions of this work include an efficient method for maintaining relaxed complementary slackness in generalized matching problems and approximation-preserving reductions between the f-matching and f-edge cover problems.






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The b-matching problem can be regarded as an f-matching problem on a multigraph in which there is implicitly an infinite supply of each edge.
Using relaxed complementary slackness, matched and unmatched edges have different eligibility criteria (to be included in augmenting paths and blossoms) whereas b-matching blossoms require that all copies of an edge—matched and unmatched alike—are all eligible or all ineligible.
These issues only arise when finding augmenting paths in batches, not one-at-a-time [11], and when the problem is f-matching, not matching.
We use \(yz_F\) and \(yz_C\) to denote the aggregated dual yz for f-matching and f-edge cover respectively. We will omit the subscript if it is clear from the context.
In an actual implementation, the inner/outer labelling can be computed in the search in Blossom Formation step. The labelling continues to be valid after contracting a maximal set of blossoms.
Of course, if \(B_v\) is inner and reachable in \(\widehat{G}\), this only implies that \(\beta (B_v)\) is reachable from an unsaturated vertex in G; other vertices in \(B_v\) may not be reachable in G.
This is because multiple augmenting walks in the underlying graph can intersect a single blossom in \(\Omega \) before we contract the blossom, while after contracting a blossom, any augmenting walk or alternating cycle going through the blossom will forbid the other walks and cycle to use the same blossom again (as it must go through the base edge).
It is still possible that later we discover some path from a descendant of C back to the root that circumvents C
Getting to the active walk does not automatically imply that you can then get to the root, since the ancestral path might not alternate at the vertex when it first reaches the active walk
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Supported by NSF grants CCF-1217338, CNS-1318294, CCF-1514383, CCF-1637546, and CCF-1815316.
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Huang, D., Pettie, S. Approximate Generalized Matching: f-Matchings and f-Edge Covers. Algorithmica 84, 1952–1992 (2022). https://doi.org/10.1007/s00453-022-00949-5
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DOI: https://doi.org/10.1007/s00453-022-00949-5