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Paper

#### A Note on Hardness of Diameter Approximation

##### Locator

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##### Fulltext (public)

arXiv:1705.02127.pdf

(Preprint), 582KB

##### Supplementary Material (public)

There is no public supplementary material available

##### Citation

Bringmann, K., & Krinninger, S. (2017). A Note on Hardness of Diameter Approximation. Retrieved from http://arxiv.org/abs/1705.02127.

Cite as: http://hdl.handle.net/11858/00-001M-0000-002D-89B7-D

##### Abstract

We revisit the hardness of approximating the diameter of a network. In the
CONGEST model, $ \tilde \Omega (n) $ rounds are necessary to compute the
diameter [Frischknecht et al. SODA'12]. Abboud et al. DISC 2016 extended this
result to sparse graphs and, at a more fine-grained level, showed that, for any
integer $ 1 \leq \ell \leq \operatorname{polylog} (n) $, distinguishing between
networks of diameter $ 4 \ell + 2 $ and $ 6 \ell + 1 $ requires $ \tilde \Omega
(n) $ rounds. We slightly tighten this result by showing that even
distinguishing between diameter $ 2 \ell + 1 $ and $ 3 \ell + 1 $ requires $
\tilde \Omega (n) $ rounds. The reduction of Abboud et al. is inspired by
recent conditional lower bounds in the RAM model, where the orthogonal vectors
problem plays a pivotal role. In our new lower bound, we make the connection to
orthogonal vectors explicit, leading to a conceptually more streamlined
exposition. This is suited for teaching both the lower bound in the CONGEST
model and the conditional lower bound in the RAM model.