Verify whether the given variables satisfy the constraints？

Answered

YJ Z

January 24, 2024 03:36

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Are there any api I can use to verify whether  specific variables given by programmer satisfy the constraints?  So that I can find  wrong constrains write by myself.

Thank you

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  Jaromił Najman

  • Gurobi Staff

  January 24, 2024 08:28

  There is no particular single function to achieve that. However, you can fix all variables to a specific value and optimize the model. If the model is infeasible then, you can compute an IIS and write it to a file to see which of the constraints and fixed values cause the infeasibility. You can open the IIS file with any standard text editor.

  A pseudo code would look something like

  model = gp.Model()
  # ...
  # construct model as usual
  # ...
  # add equality constraints to fix variables to some values
  fixedvalues = [...] # list of fixed values for variables you would like to check for feasiblity
  vars = model.getVars()
  for i in range(len(vars)):
    model.addConstr(vars[i] == fixedvalues[i])
  
  model.optimize()
  
  if model.status == GRB.OPTIMAL:
    print("Fixed point is feasible")
  elif model.status == GRB.INFEASIBLE:
    print("Fixed point is infeasible. Computing IIS")
    model.computeIIS()
    model.write("IIS.ilp")
    print("IIS written to file IIS.ilp")

  Of course you can generate the fixing equality constraints in a different way.

  Best regards, 
  Jaromił

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