During the callback process(benders decomposition), for one step, when the dual is unbounded, the unbounded ray retrieved by Gorubi is 0-vector.
I write this model to an lp file, read and optimize it. The model is feasible and unbounded but shows that the extreme ray can not be extracted.
What would that happen?
from gurobipy import *
m = read('extreme_ray.lp')
The lp file
The code result:
AttributeError: Unable to retrieve attribute 'UnbdRay'
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