## Abstract

In this paper, we introduce the concept of b-branchings in digraphs, which is a generalization of branchings serving as a counterpart of b-matchings. Here b is a positive integer vector on the vertex set of a digraph, and a b-branching is defined as a common independent set of two matroids defined by b: an arc set is a b-branching if it has at most b(v) arcs sharing the terminal vertex v, and it is an independent set of a certain sparsity matroid defined by b. We demonstrate that b-branchings yield an appropriate generalization of branchings by extending several classical results on branchings. We first present a multi-phase greedy algorithm for finding a maximum-weight b-branching. We then prove a packing theorem extending Edmonds’ disjoint branchings theorem, and provide a strongly polynomial algorithm for finding optimal disjoint b-branchings. As a consequence of the packing theorem, we prove the integer decomposition property of the bbranching polytope. Finally, we deal with a further generalization in which a matroid constraint is imposed on the b(v) arcs sharing the terminal vertex v.

Original language | English |
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Title of host publication | 43rd International Symposium on Mathematical Foundations of Computer Science, MFCS 2018 |

Editors | Igor Potapov, James Worrell, Paul Spirakis |

Publisher | Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing |

Volume | 117 |

ISBN (Print) | 9783959770866 |

DOIs | |

Publication status | Published - 2018 Aug 1 |

Event | 43rd International Symposium on Mathematical Foundations of Computer Science, MFCS 2018 - Liverpool, United Kingdom Duration: 2018 Aug 27 → 2018 Aug 31 |

### Other

Other | 43rd International Symposium on Mathematical Foundations of Computer Science, MFCS 2018 |
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Country | United Kingdom |

City | Liverpool |

Period | 18/8/27 → 18/8/31 |

## Keywords

- Arborescence
- Greedy algorithm
- Matroid intersection
- Packing
- Sparsity matroid

## ASJC Scopus subject areas

- Software