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Java Attribute Examples

Consider the case where you have a Gurobi model $m$ . You can retrieve the number of variables in the model by querying the NumVars model attribute using the get method:

  cols = m.get(GRB.IntAttr.NumVars);

If you've performed optimization on the model, the optimal objective value can be obtained by querying the ObjVal model attribute:

  obj = m.get(GRB.DoubleAttr.ObjVal);

If you'd like to query the value that a variable takes in the computed solution, you can query the X attribute for the corresponding variable object:

  vars = m.getVars()
  for (int j = 0; j < cols; j++)
    xj = vars[j].get(GRB.DoubleAttr.X)

You can also query the value of $X$

for multiple variables in a single get call on the model $m$

  double[] xvals = m.get(GRB.DoubleAttr.X, m.getVars()))

For each attribute query method, there's an analogous $set$ routine. To set the upper bound of a variable, for example:

  v = m.getVars()[0]
  v.set(GRB.DoubleAttr.UB, 0)

(In this example, we've set the upper bound for the first variable in the model to 0).