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This is a JSR331 interface for the open source Java constraint programming library "Sugar" v. 2.1.3
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package jp.kobe_u.sugar.csp;

import java.io.IOException;
import java.util.Iterator;
import java.util.Set;

import jp.kobe_u.sugar.SugarConstants;
import jp.kobe_u.sugar.SugarException;

/**
 * This class implements a comparison literal of CSP.
 * The comparison represents the condition "linearSum = 0".
 * @see CSP
 * @see LinearSum
 * @author Naoyuki Tamura ([email protected])
 */
public class LinearEqLiteral extends LinearLiteral {
    /**
     * Constructs a new comparison literal of given linear expression.
     * @param linearSum the linear expression
     */
    public LinearEqLiteral(LinearSum linearSum) {
        super(linearSum);
        cmp = "eq";
    }
    
    @Override
    public int[] getBound(IntegerVariable v) throws SugarException {
        IntegerDomain d = v.getDomain();
        int lb0 = d.getLowerBound();
        int ub0 = d.getUpperBound();
        int lb = lb0;
        int ub = ub0;
        int a = linearSum.getA(v);
        if (a > 0) {
            d = linearSum.getDomainExcept(v).neg();
            lb = ceilDiv(d.getLowerBound(), a);
            ub = floorDiv(d.getUpperBound(), a);
        } else if (a < 0) {
            d = linearSum.getDomainExcept(v);
            lb = ceilDiv(d.getLowerBound(), -a);
            ub = floorDiv(d.getUpperBound(), -a);
        }
        if (lb > ub)
            return null;
        return new int[] { lb, ub };
    }

    @Override
    public boolean isSimple() {
        return false;
    }
    
    @Override
    public boolean isValid() throws SugarException {
        IntegerDomain d = linearSum.getDomain();
        return d.size() == 1 && d.contains(0);
    }
    
    @Override
    public boolean isUnsatisfiable() throws SugarException {
        IntegerDomain d = linearSum.getDomain();
        return ! d.contains(0);
    }
    
    @Override
    public int propagate() throws SugarException {
        if (linearSum.size() == 0) {
            return 0;
        }
        int removed = 0;
        for (IntegerVariable v : linearSum.getCoef().keySet()) {
            IntegerDomain d = v.getDomain();
            int a = linearSum.getA(v);
            if (a > 0) {
                IntegerDomain d1 = linearSum.getDomainExcept(v).neg().div(a);
                int lb = d1.getLowerBound();
                int ub = d1.getUpperBound();
                removed += v.bound(lb, ub);
            } else if (a < 0) {
                IntegerDomain d1 = linearSum.getDomainExcept(v).div(- a);
                int lb = d1.getLowerBound();
                int ub = d1.getUpperBound();
                removed += v.bound(lb, ub);
            }
        }
        return removed;
    }

    @Override
    public int getCode() throws SugarException {
        throw new SugarException("Internal error " + toString()); 
    }

    /* (non-Javadoc)
     * @see Literal#isSatisfied()
     */
    @Override
    public boolean isSatisfied() {
        return linearSum.getValue() == 0;
    }
    
}