Past Meetup

Optimal Flow, Birdsong, and Merkle Trees

This Meetup is past

60 people went


With the Hands On session run last month it has been a while since we had another traditional meetup. But worry no more, two great talks again this month.

Register with Skillsmatter as well:

See you there!


• Optimal flow problems, the Edmonds-Karp algorithm, and birdsong - Dan Stowell (@mclduk (

Imagine you have to send as many trains-per-hour as possible from London to Edinburgh, and that different segments of the route have different maximum capacities. This is a "maximum flow" problem. They're often more difficult than A-to-B routing problems such as a car SatNav solves, because the solution is a network rather than a single path, so the search space is bigger. There are however some very elegant maximum flow algorithms. I'll describe a neat one called the Edmonds-Karp algorithm, which can be understood pictorially. I'll also tell you how I applied it in my research to detect which bird is singing when! It's an example of transforming a problem just enough that you find that graph theory has already solved it.

Bio: Dan Stowell is a researcher applying machine learning to sound. He has worked on voice, music, birdsong and environmental soundscapes. He was recently awarded an EPSRC Early Career research fellowship, based at QMUL, where he is developing new techniques in structured machine listening for soundscapes with multiple birds.

• Certificate Transparency, an authenticated data structure - Tom Fitzhenry

Certificate Transparency aims to mitigate the problem of misissued SSL certificates. It does this using an authenticated data structure: an auditable, append-only, untrusted logs of all issued certificates. The append-only property of each log is technically achieved using Merkle Trees, which can be used to efficiently show that any particular version of the log is a superset of any particular previous version.

Bio: Tom Fitzhenry is a senior software developer at Blinkbox. He is interested in security, a contributor to Certificate Transparency, and has a Mathematics degree.