Adding Variables Objectives and Constraints

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First, we need to set up the objective and the degree constraints. First, add the following fields to the class

private IloCplex cplex;
private TspInstance<V,E> tspInstance;
private final ImmutableBiMap<E,IloIntVar> edgeVariables;

and initialize them, as below.

	public TspIpSolver(TspInstance<V,E> tspInstance, EnumSet<Option> options) throws IloException{
		this.options = options;
		this.tspInstance = tspInstance;
		this.cplex = new IloCplex();
		UndirectedGraph<V,E> graph = tspInstance.getGraph(); //for convenience, we will be using this a lot
		this.edgeVariables = Util.makeBinaryVariables(cplex, graph.getEdges());
		//the degree constraints
		//the objective		
	}

The constraints and objective still need to be added to the cplex object. Try adding them yourself! The following methods should be useful for making the constraints:

From Util, public static <T> IloLinearIntExpr integerSum(IloCplex cplex, BiMap<T,IloIntVar> variables, Iterable<T> set)
- For each element
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  e
  of set, finds the corresponding variable
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  x_e
  and returns
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  \sum_{e \in \text{set}} x_e
From IloCplex, public IloRange addEq(IloNumExpr e, double v)
- Adds the equality constraint e = v
From UndirectedGraph<V,E>, public Collection<E> getIncidentEdges(V vertex)
- returns the edges of the graph that are incident to vertex

If you are unfamiliar with Java, consider viewing the solution for the constraint, then trying the objective yourself.
Solution

For the objective, we need the functions:

From Util, public static <T> IloLinearNumExpr sum(IloCplex cplex, BiMap<T,IloIntVar> variables, Iterable<T> set, Function<? super T,? extends Number> coefficients)
- For every element
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  e
  of set, gets the corresponding variable
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  x_e
  from variables and the number
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  d_e
  from coefficients and returns an expression for
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  \sum_{e \in \text{set}} d_e x_e
  .

Solution

Child pages

Adding Variables Objectives and Constraints