user31712: There is a 2016 paper from Bitfury on a proposed routing algorithm for LN:
Flare: An Approach to Routing
in Lightning Network
What is the relation between it and was was actually implemented (the primary reference being the BOLT specs)?

user81940: As far as I know flare was never implemented for lightning nodes and is not being used. I think current implementations use sind pathfinding algorithms like BfS or  Dijkstra. The pathfinding itself is not part of the BOLTs anyway. A node could do whatever it wants with the information provided from the gossip store / gossip protocol. (BOLT 07). People could in particular decide to go for the approach given by flare. 

31712: <p>There is a 2016 paper from Bitfury on a proposed routing algorithm for LN:</p>

<p><a href="https://bitfury.com/content/downloads/whitepaper_flare_an_approach_to_routing_in_lightning_network_7_7_2016.pdf" rel="nofollow noreferrer">Flare: An Approach to Routing
in Lightning Network</a></p>

<p>What is the relation between it and was was actually implemented (the primary reference being the <a href="https://github.com/lightningnetwork/lightning-rfc/blob/master/00-introduction.md" rel="nofollow noreferrer">BOLT specs</a>)?</p>
 81940: <p>As far as I know flare was never implemented for lightning nodes and is not being used. I think current implementations use sind pathfinding algorithms like BfS or  Dijkstra. The pathfinding itself is not part of the BOLTs anyway. A node could do whatever it wants with the information provided from the gossip store / gossip protocol. (BOLT 07). People could in particular decide to go for the approach given by flare. </p>
