cbCut - Variable not in model

Answered

Wenbo Ma

November 15, 2021 15:57

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Hi, I was trying to add a user-cut through callback but encountered an error that I cannot resolve. There was always an GurobiError returned saying 'Variable not in model' due to the last 'model.cbCut' command while the print function in the previous line has no issue to find the variable gamma

def add_valid_cut(model, where):
    if where == GRB.Callback.MIPNODE:
        status = model.cbGet(GRB.Callback.MIPNODE_STATUS)
        if status == GRB.OPTIMAL:
            print('valid ineqaulities added')
            rel = model.cbGetNodeRel(gamma)
            for base in train_drone_bases:
            if rel[base, 1] > 1 - rel[base, 2]:
                print(base, 'valid cut added')
                print(gamma[1,1], 'gamma', gamma[1,2])
                model.cbCut((gamma[1,1] <= 1 - gamma[1,2]))

0

• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  June 23, 2025 02:44 Edited

  This post is more than three years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum. Or why not try our AI Gurobot?.
• 

  Jaromił Najman

  • Gurobi Staff

  November 17, 2021 09:47 Edited

  It is not possible to access variables \(\texttt{gamma}\) from inside your callback, because the model at this point doesn't know them. You have to save these variables as a private model object as is done in, e.g., the tsp.py example.

  So your code should read something like

  def add_valid_cut(model, where):
      if where == GRB.Callback.MIPNODE:
          status = model.cbGet(GRB.Callback.MIPNODE_STATUS)
          if status == GRB.OPTIMAL:
              print('valid ineqaulities added')
              rel = model.cbGetNodeRel(model._gamma)
              for base in train_drone_bases:
              if rel[base, 1] > 1 - rel[base, 2]:
                  print(base, 'valid cut added')
                  print(model._gamma[1,1], 'gamma', model._gamma[1,2])
                  model.cbCut((model._gamma[1,1] <= 1 - model._gamma[1,2]))
  
  
  model = Model("myModel")
  gamma = model.addVars(...)
  model._gamma = gamma
  [...]
  model.optimize(add_valid_cut)

  Best regards,
  Jaromił

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