[jplewicke]

Ripple is actually a generalized network flow problem, in which the flow through an edge can be multiplied by an exchange rate when converting between currencies. As a result, regular network flow algorithms don't apply. There's also another issue with using a minimum cost criterion, since the costs are in different currencies and it's not clear how to put them on the same footing.

[murbard2]

If you make cost the log of the conversion rate plus the log of the %age fee, and treat each node as a distinct node for each currency, you do get max flow min cost.