How to use addVars() in GurobiPy using "if" conditional?

Answered

Vincent

November 29, 2020 22:51

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I have defined a variable using addVar() method as follows:

for i in range(no_nodes):
  for j in range(no_nodes):
    for k in O:
      if fij[i][j]==1 or mij[i][j]==1:
        x[i,j,k] = m.addVar(vtype=GRB.INTEGER, name="x[%s,%s,%s]" %(i,j,k))

where fij and mij are model's parameters and O is an unordered set containing more than 1000 elements.

It works properly, and there is no issue in solving the model. I just wonder how this variable definition can be revised by applying the addVars() method instead of addVar()?

Thanks.

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• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  December 06, 2024 00:39

  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?.
• 

  Matthias Miltenberger

  • Gurobi Staff

  November 30, 2020 13:35 Edited

  Hi Vincent!

  You can do the following to use addVars() and reduce the code to a single line:

  x = m.addVars([(i,j,k) for i in no_nodes for j in no_nodes for k in O if fij[i][j] or mij[i][j]],
      vtype=GRB.INTEGER, name="x")

  The name property will automatically be indexed for every single variable and assuming that fij and mij are binaries, you can also omit the "==1" part.

  You may also use itertools.product:

  from itertools import product
  x = m.addVars([(i,j,k) for (i,j) in product(no_nodes,repeat=2) for k in O if fij[i][j] or mij[i][j]],
      vtype=GRB.INTEGER, name="x")

  Cheers,
  Matthias

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  Vincent

  November 30, 2020 18:53 Edited

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  Hi Matthias,

  Thanks for your help. Is the itertools.product method faster than the first one?

  Thanks,
  Vincent

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  Matthias Miltenberger

  • Gurobi Staff

  December 02, 2020 11:57

  Hi Vincent,

  Honestly, I wouldn't worry about the performance of either implementation. Most likely, adding the variables is more expensive than looping over your lists. I would go with the implementation that results in more readable, maintainable, and extendable code.

  Cheers,
  Matthias

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