Using CPLEX in TspIpSolver
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;
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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
}
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The constraints and objective still need to be added to the cplex object. Try adding them yourself! The following methods (as defined in Solver Specification and Java Style for CPLEX) should be useful for making the constraints:
- From
Util , the static method integerSum(IloCplex cplex, BiMap<T,IloIntVar> variables, Iterable<T> set)
- From
IloCplex , the method addEq(IloNumExpr e, double v)
- From
UndirectedGraph<V,E> , the method getIncidentEdges(V vertex)
If you are unfamiliar with Java, consider viewing the solution for the constraint, then trying the objective yourself.
Solution
//the degree constraints
for(V vertex: graph.getVertices()){
cplex.addEq(Util.integerSum(cplex, edgeVariables,
graph.getIncidentEdges(vertex)), 2);
}
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For the objective, we need the functions:
- From
Util , the static method sum(IloCplex cplex, BiMap<T,IloIntVar> variables, Iterable<T> set, Function<? super T,? extends Number> coefficients)
- From
UndirectedGraph<V,E> , the method getEdges()
- From
TspInstance , the method getEdgeWeights
Solution
//the objective
cplex.addMinimize(Util.integerSum(
cplex, edgeVariables, graph.getEdges(),tspInstance.getEdgeWeights()));
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