Multiscenario python returns same solution for each scenario
OngoingI ran the example https://www.gurobi.com/documentation/9.0/examples/multiscenario_py.html and the output is the same for each scenario:
| Plant |
Scenario | 0 1 2 3 4 | Costs Name
0 | x | 210500 Base model
1 | x | 210500 Increased warehouse demands
2 | x | 210500 Double the warehouse demands
3 | x | 210500 Decreased plant fixed costs
4 | x | 210500 Increased warehouse demands and decreased plant fixed costs
5 | x | 210500 Force plant with largest fixed cost to stay open
6 | x | 210500 Force plant with smallest fixed cost to be closed
Running:
for s in range(m.NumScenarios):
print("scenario: {}".format(s))
# set scenario number
m.Params.ScenarioNumber = s
print("scenario name: {}".format(m.ScenNName))
print("scenario objective value: {}".format(m.ScenNObjVal))
results in a changing scenario name. However, the value ScenNObjVal is not updated and remains the same for each s in m.NumScenarios.
How do I retrieve the objective values for different scenarios? Is the example on the Gurobi website incorrect?
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Official comment
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Gurobi Staff
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Hi Olaf,
Is it possible that you are working on a Compute Server or Cloud? If yes, then you have to call the Model.update() function after setting the scenario to properly update the cached values, i.e.,
m.Params.ScenarioNumber = s
m.update()
# rest of the codeBest regards,
Jaromił0 -
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Yes! Thanks a lot.
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Please note that this behavior has been fixed for Gurobi 9.0.3 and adding the update() call is not necessary for that version.
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