# Online Directed Spanners and Steiner Forests

arXiv: https://arxiv.org/abs/2103.04543 · HTML: https://mlsanity.com/paper/2103.04543/

## Key facts

- Cited by 1 papers in the map (data through 14 Oct 2026).
- First posted on arXiv 8 Mar 2021.

## Built on by (most cited first, 1 of 1)

- [Learning-Augmented Algorithms for Online Linear and Semidefinite Programming](https://mlsanity.com/paper/2209.10614/) (2022)

## Abstract (arXiv)

We present online algorithms for directed spanners and Steiner forests. These problems fall under the unifying framework of online covering linear programming formulations, developed by Buchbinder and Naor (MOR, 34, 2009), based on primal-dual techniques. Our results include the following: For the pairwise spanner problem, in which the pairs of vertices to be spanned arrive online, we present an efficient randomized tildeO(n4/5)-competitive algorithm for graphs with general lengths, where n is the number of vertices. With uniform lengths, we give an efficient randomized tildeO(n2/3+ε)-competitive algorithm, and an efficient deterministic tildeO(k1/2+ε)-competitive algorithm, where k is the number of terminal pairs. These are the first online algorithms for directed spanners. In the offline setting, the current best approximation ratio with uniform lengths is tildeO(n3/5 + ε), due to Chlamtac, Dinitz, Kortsarz, and Laekhanukit (TALG 2020). For the directed Steiner forest problem with uniform costs, in which the pairs of vertices to be connected arrive online, we present an efficient randomized tildeO(n2/3 + ε)-competitive algorithm. The state-of-the-art online algorithm for general costs is due to Chakrabarty, Ene, Krishnaswamy, and Panigrahi (SICOMP 2018) and is tildeO(k1/2 + ε)-competitive. In the offline version, the current best approximation ratio with uniform costs is tildeO(n4/7 + ε), due to Abboud and Bodwin (SODA 2018). A small modification of the online covering framework by Buchbinder and Naor implies a polynomial-time primal-dual approach with separation oracles, which a priori might perform exponentially many calls. We convert the online spanner problem and the online Steiner forest problem into online covering problems and round in a problem-specific fashion.