How to get number of binary variables and number of continous variables after doing optimisation?

Answered

Margi Shah

• October 06, 2023 08:52

I run a model using Gurobi. I want to find the number of binary variables and continuous variables of the model. How do I do it?

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  Lennart Lahrs

  Gurobi Staff

  • October 06, 2023 09:26
  • Edited

  Hi Margi,

  The Gurobi log outputs the number of continuous, integer, and binary variables.
  Note that any binary variable is also considered an integer variable. E.g.:

  Optimize a model with 0 rows, 3 columns and 0 nonzeros
  Model fingerprint: 0x5fa75176
  Variable types: 1 continuous, 2 integer (1 binary)

  Using the Gurobi Python API, you can access the information like shown below. The number of continuous variables is the total number of variables minus the number of integer variables. You can also get a list of all variables and check variable types individually.

  import gurobipy as gp
  from gurobipy import GRB
  
  m = gp.Model()
  m.addVar(vtype=GRB.CONTINUOUS)
  m.addVar(vtype=GRB.INTEGER)
  m.addVar(vtype=GRB.BINARY)
  m.optimize()
  assert m.NumVars == 3
  assert m.NumIntVars == 2
  assert m.NumBinVars == 1
  
  vars = m.getVars()
  assert vars[0].VType == GRB.CONTINUOUS
  assert vars[1].VType == GRB.INTEGER
  assert vars[2].VType == GRB.BINARY

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