Multiplies the two-event Expected Force by the logarithm of alpha times
seed degree (Lawyer 2015, equation 2). Alpha defaults to two, as in the
paper, and must be finite and strictly greater than one. Directed input
uses outgoing degree, consistent with the outgoing transmission process.
An isolate scores zero without evaluating the logarithm of zero.
All graph, event-counting and zero-force conventions of
centrality_expected_force apply. Native log addition avoids
overflow when alpha times degree cannot be represented.