Bad News:
Not approximable within 2
for any
[421].
Comment:
Not in APX if the distances do not satisfy the triangle inequality.
MAXIMUM EDGE SUBGRAPH is the variation where the measure is the average
distance between any pair of facilities [421].
Variation in which we allow the points in F to lie in edges (considered as
curves) is also approximable within 2 and is not approximable within
[449].