org.chocosolver.graphsolver.cstrs.symmbreaking.PropSymmetryBreaking Maven / Gradle / Ivy

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A graph module for Choco Solver.

There is a newer version: 4.2.2

package org.chocosolver.graphsolver.cstrs.symmbreaking;

import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.PropagatorPriority;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.variables.BoolVar;
import org.chocosolver.util.ESat;

/**
 * @author Моклев Вячеслав
 */
public class PropSymmetryBreaking extends Propagator {

	private int n;
	private BoolVar[] t;

	public PropSymmetryBreaking(BoolVar[] t) {
		super(t, PropagatorPriority.QUADRATIC, false);
		n = (int) Math.round(Math.sqrt(t.length));
		this.t = t;
	}

	private enum Cmp {
		LESS, EQUALS, GREATER, UNDEFINED
	}

	private Cmp compare(BoolVar a, BoolVar b) throws ContradictionException {
		if (a.isInstantiatedTo(0) && b.isInstantiatedTo(1)) {
			return Cmp.LESS;
		}
		if ((a.isInstantiatedTo(0) && b.isInstantiatedTo(0)) || (a.isInstantiatedTo(1) && b.isInstantiatedTo(1))) {
			return Cmp.EQUALS;
		}
		if (a.isInstantiatedTo(1) && b.isInstantiatedTo(0)) {
			return Cmp.GREATER;
		}
		return Cmp.UNDEFINED;
	}

	private boolean lessOrEquals(int j1, int j2) throws ContradictionException {
		for (int i = 0; i < n; i++) {
			if (t[i + j1 * n].isInstantiatedTo(1)) {
				t[i + j2 * n].instantiateTo(1, this);
			}
			Cmp cmp = compare(t[i + j1 * n], t[i + j2 * n]);
			// lexicographically less or undefined
			if (cmp == Cmp.LESS || cmp == Cmp.UNDEFINED) {
				return true;
			}
			// lexicographically greater
			if (cmp == Cmp.GREATER) {
				return false;
			}
		}
		// entirely equals
		return true;
	}

	private boolean sorted() throws ContradictionException {
		for (int j = 0; j < n - 1; j++) {
			if (!lessOrEquals(j, j + 1)) {
				return false;
			}
		}
		return true;
	}

	@Override
	public void propagate(int evtmask) throws ContradictionException {
		if (!sorted()) {
			throw new ContradictionException();
		}
	}

	@Override
	public ESat isEntailed() {
		try {
			if (!sorted()) {
				return ESat.FALSE;
			}
		} catch (ContradictionException e) {
			return ESat.FALSE;
		}
		for (BoolVar aT : t) {
			if (!aT.isInstantiated()) {
				return ESat.UNDEFINED;
			}
		}
		return ESat.TRUE;
	}
}