I am using the algorithm implemented by the library
networkx to solve a Steiner minimal tree problem.
They claim their algorithm to give an approximated solution.
However, I am working on a specific group of graphs, namely, grid lattices (with capacity 1).
I believe this group of circuit belongs the Euclidean group, which should be hard to solve as well(?).
On my experiments I keep getting the optimal solutions, so I wonder what property my graph has to guarantee that. Is it because of the capacity? Or maybe because it is a grid?