2D bin packing problem

Answered

Faria Kalim

March 25, 2020 02:32

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Hi, 

I am trying to solve a 2D bin packing problem. I have three types of bins where each bin has an associated cost. The problem's objective is to minimize the total cost of using bins. Thus, the number of each bin type is a variable. So I can have 0 number of the first bin, 10 of the second and 5 of the third bin, if that means all balls fit and this is the minimum cost. However, I am having trouble expressing a variable number of bins through the python API. This is my current attempt: machines = [] # this list is meant to contain all the finally used bins def create_num_machines():      num_machines = len(machines_lcm) # machines_lcm contains the original bins      variables = []      for i in range(0, num_machines):          variable = m.addVar(vtype = GRB.INTEGER, lb = 0, ub = 10, name = "m" + str(i))           for x in range (0, variable):              machines.append(machines_lcm[i])          variables.append(variable)      return variables However, this gives me the following error at the line 'for x in range (0, variable)': 'TypeError: 'Var' object cannot be interpreted as an integer' How do I avoid this?

 

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• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  June 23, 2025 03:16 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?.
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  Darren O'Connor

  April 14, 2020 04:37

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  Hi Faria, I have a similar problem to model. Did you find an answer for this? - Darren

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  Jaromił Najman

  • Gurobi Staff

  September 04, 2020 13:17 Edited

  Hi,

  In your code snippet, \(\texttt{variable}\) is a Var object. The \(\texttt{range}\) function requires two integer objects as arguments thus, you get the \(\texttt{TypeError}\). It should be enough for your problem to replace \(\texttt{range(0, variable)}\) with \(\texttt{range(0, i)}\).

  Best regards,
  Jaromił

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