Can the callback function combine two check mechanism?(TSP subtour elimination + Bender's decomposition)
AnsweredHello, I use callback function to optimize a MIP problem.
if where == GRB.Callback.MIPSOL:
selected = gb.tuplelist((i, j) for i in range(N + 1) for j in range(N + 1)
if model.cbGetSolution(model.getVarByName('r_' + str(i) + str(j))) > 0.5)
# find the shortest cycle in the selected edge list
tour = self.subtour(selected)
if len(tour) < N+1:
# Add the subtour elimination constraint
# ...
# ...
else:
# Bender's cut
LB = model.cbGet(GRB.Callback.MIPSOL_OBJBND)
status, UB = sub_problem(z_1)
if status == 3:
# Add the feasibility cut
# ...
if status == 2:
if abs(UB  LB) >= 0.1:
# Add the optimality cut
elif len(tour) == N:
model.terminate()
The logic is quite clear. However, it doesn't terminate according to the termination condition. It ends automatically and the length of tour is less than N. I don't know what's wrong with my code... And I want to know why the callback process would end by itself???
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I have verified that all the lazy constraints' formulations are correct。。。
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Hi Jacob,
Could you briefly explain what is \(\texttt{N}\) in your code snippet?
The case \(\texttt{len(tour) == N}\) cannot be reached because it always lands in \(\texttt{len(tour) < N+1}\).
Best regards,
Jaromił0
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