/**
* Creates a directed tree constraint : g forms an arborescence rooted in vertex 'root' i.e. g has
* no circuit and a path exists from the root to every node
*
* @param g a directed graph variable
* @param root the (fixed) root of the tree
* @return a directed tree constraint
*/
public static Constraint directed_tree(IDirectedGraphVar g, int root) {
int n = g.getNbMaxNodes();
int[] nbPreds = new int[n];
for (int i = 0; i < n; i++) {
nbPreds[i] = 1;
}
nbPreds[root] = 0;
return new Constraint(
"directed_tree",
new PropArborescence(g, root),
new PropNodeDegree_AtMost_Coarse(g, Orientation.PREDECESSORS, nbPreds),
new PropNodeDegree_AtLeast_Incr(g, Orientation.PREDECESSORS, nbPreds));
}
/**
* g must form a circuit
*
* @param g a directed graph variable
* @return a circuit constraint
*/
public static Constraint circuit(IDirectedGraphVar g) {
if (g.getMandatoryNodes().getSize() == g.getNbMaxNodes()) {
return hamiltonian_circuit(g);
}
return new Constraint(
"circuit",
new PropNodeDegree_AtLeast_Incr(g, Orientation.SUCCESSORS, 1),
new PropNodeDegree_AtLeast_Incr(g, Orientation.PREDECESSORS, 1),
new PropNodeDegree_AtMost_Incr(g, Orientation.SUCCESSORS, 1),
new PropNodeDegree_AtMost_Incr(g, Orientation.PREDECESSORS, 1),
new PropNbSCC(g, g.getSolver().ONE),
new PropCircuit(g));
}
/**
* Creates a path constraint : g forms a path from node 'from' to node 'to' Basic but fast
* propagation
*
* @param g a directed graph variable
* @param from an integer variable
* @param to an integer variable
* @return a path constraint
*/
public static Constraint path(IDirectedGraphVar g, int from, int to) {
int n = g.getNbMaxNodes();
int[] succs = new int[n];
int[] preds = new int[n];
for (int i = 0; i < n; i++) {
succs[i] = preds[i] = 1;
}
succs[to] = preds[from] = 0;
Propagator[] props =
new Propagator[] {
new PropNodeDegree_AtLeast_Coarse(g, Orientation.SUCCESSORS, succs),
new PropNodeDegree_AtMost_Incr(g, Orientation.SUCCESSORS, succs),
new PropNodeDegree_AtLeast_Coarse(g, Orientation.PREDECESSORS, preds),
new PropNodeDegree_AtMost_Incr(g, Orientation.PREDECESSORS, preds),
new PropPathNoCircuit(g)
};
return new Constraint("path", props);
}
/**
* Creates a strong connectedness constraint which ensures that g is strongly connected
*
* @param g a directed graph variable
* @return A strong connectedness constraint which ensures that g is strongly connected
*/
public static Constraint strongly_connected(IDirectedGraphVar g) {
return nb_strongly_connected_components(
g, VF.bounded("nbSCC", 0, g.getNbMaxNodes(), g.getSolver()));
}