My guess is that the answer is wrong. Instead of pairing with Billy, Mary can easily connect to Dustin and Alecia can then pair with Billy. When I run the results in Table to get maximum flows value I get 3 or 4. Am I wrong or is there something strange with the FindMaximumFlow function?
Yep, broken, specifically with vertex capacities (not edge capacities). I have a little notebook with some of these bugs. It’s been sent to WRI more than once.
Now fd["FlowTable"] and fd["ResidualGraph"] don’t work. Retrieving multiple properties also doesn’t work, despite being documented: fd[{"CostValue", "EdgeList"}].
Some of these problems actually show in the documentation notebooks. You can also check online, just open Scope, and you’ll see the bugs immediately in the Out[] cells. OptimumFlowData—Wolfram Documentation
There was a recent Twitch stream dealing with Graph stuff, and you can see bug counts mentioned in the meeting notebooks. It sounded as if there were a new drive to eliminate some of these bugs.