IIS infeasible

回答済み

Vida Yousefinezhad

2024年02月08日 22:29 編集済み

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Hi, 
I have a maximization problem, which is infeasible (status: 4) in Python with the Gurobi package. Then, I tried to do IIS infeasible to find out the constraints that make the model infeasible. But it does not show information on infeasibility and just shows LP format. How can I solve this issue. I really appreciate if anyone helps me. My code is as follows:

# Check the status of the optimization
status = model.status
print("Status:", status)

# If the model is infeasible, print infeasible constraints
if status == GRB.INFEASIBLE:
    print("Model is infeasible.")
    try:
        model.computeIIS()
        infeasible_constraints = [c.constrName for c in model.getConstrs() if c.IISConstr]
        print("Infeasible constraints:", infeasible_constraints)
        print("Number of infeasible constraints:", len(infeasible_constraints))
        print("Total number of constraints:", model.NumConstrs)
    except gp.GurobiError as e:
        print("Failed to compute IIS:", e)

# Save the Gurobi log to a file
log_file_path = "gurobi_log.lp"  # Path to save the log file with .lp extension
model.write("gurobi_log.lp")

# Read the Gurobi log file
with open(log_file_path, 'r') as log_file:
    log_contents = log_file.read()

# Print the log contents
print("Gurobi Optimizer Log:")
print(log_contents)

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  Riley Clement

  • Gurobi Staff

  2024年02月09日 02:21

  Hi Vida,

  It would be worthwhile taking a thorough look at the documentation on computeIIS.

  You need to use a .ilp extension to write the IIS.  Using a .lp extension will simply write the original model.

  - Riley

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  Vida Yousefinezhad

  2024年02月10日 10:18

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  Hi Riley,

  Thank you for your help. In my case, I could not extract IIS because there was a problem in my linearization with max function. So, I could not see any results for computing IIS. 

  -Vida

   

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