gurobipy.GurobiError: Divisor must be a constant

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Danning Xie

2022年03月07日 16:56

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I was trying to add an objective function to maximize the average probability:

model.setObjectiveN(-sum(x[i,j]*prob[i][j] for i in range(n) for j in range(m))/x.sum(), index=0)

where x is variable defined as:

x = model.addVars(n,m, vtype=GRB.BINARY)

and `prob` is a matrix of size n*m which is previously known data.

 

But I got error

Traceback (most recent call last):
  File "src/gurobipy/linexpr.pxi", line 523, in gurobipy.LinExpr.__truediv__
TypeError: float() argument must be a string or a number, not 'gurobipy.LinExpr'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "constr_solver.py", line 172, in <module>
    main(...)
  File "constr_solver.py", line 137, in main
    x = optimize(...)
  File "constr_solver.py", line 72, in optimize
    model.setObjectiveN(-sum(x[i,j]*prob[i][j] for i in range(n) for j in range(m))/x.sum(), index=0)
  File "src/gurobipy/linexpr.pxi", line 525, in gurobipy.LinExpr.__truediv__
gurobipy.GurobiError: Divisor must be a constant

 

 

 

I want to maximize the average probability for the chosen x.  Is there any other way I can define this? Thank you

 

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• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2025年11月16日 23:42

  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 try Gurobot, our chatbot interface offering instant, expert-level support.
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  Jaromił Najman

  • Gurobi Staff

  2022年03月08日 10:54 編集済み

  Dividing by a variable (or a sum of variables) is currently not supported in Gurobi. However, with a few auxiliary variables and equality constraints, it is possible to formulate your objective function in Gurobi.

  To formulate a division by an optimization variable, you should introduce an auxiliary variable \(z_n\) for the numerator expression and an auxiliary variable \(z_d\) for the denominator expression, i.e., add equality constraints \(z_n = \text{numerator}\) and \(z_d = \text{denominator}\).
  Next, you can follow the instructions in How do I divide by a variable in Gurobi? to model the division \(\frac{1}{z_d} = x\).
  You can then finally use \(x\) and \(z_n\) in your objective function as \(z_n \cdot x\).
  Please note that your model is nonconvex and you have to set the NonConvex parameter.

  Best regards, 
  Jaromił

   

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  Danning Xie

  2022年03月09日 17:15

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  Thank you! It helps. 

   

   

  Danning

  0

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