Gurobi callback function and performance

Ongoing

Lovelesh gupta

• October 22, 2021 11:08

I was planning to use callbacks to implement terminate model run, based on certain checks. Is there any known limitation or performance impact due to callbacks? 

Do callback block the actual model run? based on my minimal testing I dont see that happening. wanted to confirm

Any guideline on what should not be done in callbacks? 

Related to

• Callbacks

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• Official comment

  

  Simranjit Kaur

  Gurobi Staff

  • December 06, 2024 00:24

  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?.
• 

  Tobias Achterberg

  Gurobi Staff

  • October 22, 2021 13:19

  Having an empty callback should not deteriorate performance much. If you are using Python, then of course a callback means that we need to always step into the Python interpreter, but even this shouldn't affect performance significantly, maybe except for corner cases like really small models on which Gurobi processes super many branch-and-bound tree nodes per second.

  While the callback is executed, everything else comes to a halt. So, if you are doing heavy computations inside your callback, then this will slow down the overall process.

  Regards,

  Tobias

   

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• 

  Namrita Varshney

  • January 16, 2024 15:20

  

  

  

   is it true that Gurobi always executes the callback only after finding the feasible solution?? or it can be the case that during the callback gurobi does not have the complete model solution??

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• 

  Riley Clement

  Gurobi Staff

  • January 16, 2024 23:34

  Hi Namrita,

  No, this is not true.  Please take a look at the following links:

  Callbacks
  Callback Codes
  callback.py

  - Riley

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• 

  Namrita Varshney

  • January 17, 2024 05:07
  • Edited

  

  

  

  thank you for reply.
  look at the code , I was not able to add   sol = model.cbGetSolution(variables) in callback_tree function, So I created a dictionary to find my solution , 
  it can be the case the the solution gurobi find during this callback , it might not satisfy all the constraint
  
  def mycallback(model, where):
      if not hasattr(model, '_last_print_time'):
          model._last_print_time = time.time()
          model._last_sol = ""

      if where == GRB.Callback.MIPSOL:
          objVal = model.cbGet(GRB.Callback.MIPSOL_OBJ)
          current_time = time.time()
          if current_time - model._last_print_time >= 10:
              variables = model.getVars()
              sol = model.cbGetSolution(variables)
              variable_dict = {var: value for var,value in zip(variables,sol)}

              root = model._root 
              print_tree(root)            
              print("==================================================")
              print("Hiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii  callback  ")
              listt = set()
              listt = callback_tree(model,root, sol, variable_dict,listt)
              print("==================================================")
              
       
              intermediate_sol ,taut_list,flag =process_intermediat_tree(model,root)
              # print(taut_list)
              
              
              if flag == 1:
                  msg = f"{listt} lazy constraint added "
                  print(msg)
                  lazy_constr = gp.quicksum(model.getVarByName(var) for var in listt) <= len(listt) - 1
                  model.cbLazy(lazy_constr)
                  model._sol = ""
              if intermediate_sol == model._sol and model.RUNTIME > 1500 and current_time - model._last_print_time >= 500 and model._sol != "":
                  print("model._countsol: ",model._countsol)
                  # model._countsol += 1
                  # if model._countsol > 4:
                  print("No change in sol")
                  model.terminate()

              model._last_print_time = current_time
              
              
  def callback_tree(model, root, sol, variable_dict,listt):
      if root is None:
          return listt
      
      value = root.node_number
      print(f"-------------------------------------------------------I am at a node {root.node_number} {root.value}------------------------------")
      # print(f"-------------------------------------------------{variable_dict[model.getVarByName(str(root.value)+str(root.node_number))]}------------------------------")
      flag=0
      for v in decl.all_list:
          varname = str(v) + str(value)
          # print(f"-------------------varname: {varname}-------------------")
          # print(type(varname))      
          var_value = variable_dict[model.getVarByName(varname)]
              
          if var_value ==1:
              flag =1
              print(f" {varname} is true")
              listt.add(varname)
              root.value = v

      if flag==0:
          print(f"Variables not found. {root.node_number}  {root.value}")
          
      listt.update(callback_tree(model, root.left, sol, variable_dict,listt))
      listt.update(callback_tree(model, root.right, sol, variable_dict,listt))
      return listt

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