sos.py

#!/usr/bin/env python3.11

# Copyright 2025, Gurobi Optimization, LLC

# This example creates a very simple Special Ordered Set (SOS) model.
# The model consists of 3 continuous variables, no linear constraints,
# and a pair of SOS constraints of type 1.

import gurobipy as gp
from gurobipy import GRB

try:
    # Create a new model

    model = gp.Model("sos")

    # Create variables

    x0 = model.addVar(ub=1.0, name="x0")
    x1 = model.addVar(ub=1.0, name="x1")
    x2 = model.addVar(ub=2.0, name="x2")

    # Set objective
    model.setObjective(2 * x0 + x1 + x2, GRB.MAXIMIZE)

    # Add first SOS: x0 = 0 or x1 = 0
    model.addSOS(GRB.SOS_TYPE1, [x0, x1], [1, 2])

    # Add second SOS: x0 = 0 or x2 = 0
    model.addSOS(GRB.SOS_TYPE1, [x0, x2], [1, 2])

    model.optimize()

    for v in model.getVars():
        print(f"{v.VarName} {v.X:g}")

    print(f"Obj: {model.ObjVal:g}")

except gp.GurobiError as e:
    print(f"Error code {e.errno}: {e}")

except AttributeError:
    print("Encountered an attribute error")