/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.math.optimization.linear;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

import org.apache.commons.math.linear.MatrixUtils;
import org.apache.commons.math.linear.RealVector;
import org.apache.commons.math.linear.ArrayRealVector;

/**
 * An objective function for a linear optimization problem.
 * <p>
 * A linear objective function has one the form:
 * 
 * <pre>
 * c<sub>1</sub>x<sub>1</sub> + ... c<sub>n</sub>x<sub>n</sub> + d
 * </pre>
 * 
 * The c<sub>i</sub> and d are the coefficients of the equation, the
 * x<sub>i</sub> are the coordinates of the current point.
 * </p>
 * 
 * @version $Revision$ $Date$
 * @since 2.0
 */
public class LinearObjectiveFunction implements Serializable {

	/** Serializable version identifier. */
	private static final long serialVersionUID = -4531815507568396090L;

	/** Coefficients of the constraint (c<sub>i</sub>). */
	private final transient RealVector coefficients;

	/** Constant term of the linear equation. */
	private final double constantTerm;

	/**
	 * @param coefficients
	 *            The coefficients for the linear equation being optimized
	 * @param constantTerm
	 *            The constant term of the linear equation
	 */
	public LinearObjectiveFunction(double[] coefficients, double constantTerm) {
		this(new ArrayRealVector(coefficients), constantTerm);
	}

	/**
	 * @param coefficients
	 *            The coefficients for the linear equation being optimized
	 * @param constantTerm
	 *            The constant term of the linear equation
	 */
	public LinearObjectiveFunction(RealVector coefficients, double constantTerm) {
		this.coefficients = coefficients;
		this.constantTerm = constantTerm;
	}

	/**
	 * Get the coefficients of the linear equation being optimized.
	 * 
	 * @return coefficients of the linear equation being optimized
	 */
	public RealVector getCoefficients() {
		return coefficients;
	}

	/**
	 * Get the constant of the linear equation being optimized.
	 * 
	 * @return constant of the linear equation being optimized
	 */
	public double getConstantTerm() {
		return constantTerm;
	}

	/**
	 * Compute the value of the linear equation at the current point
	 * 
	 * @param point
	 *            point at which linear equation must be evaluated
	 * @return value of the linear equation at the current point
	 */
	public double getValue(final double[] point) {
		return coefficients.dotProduct(point) + constantTerm;
	}

	/**
	 * Compute the value of the linear equation at the current point
	 * 
	 * @param point
	 *            point at which linear equation must be evaluated
	 * @return value of the linear equation at the current point
	 */
	public double getValue(final RealVector point) {
		return coefficients.dotProduct(point) + constantTerm;
	}

	/** {@inheritDoc} */
	@Override
	public boolean equals(Object other) {

		if (this == other) {
			return true;
		}

		if (other == null) {
			return false;
		}

		try {

			LinearObjectiveFunction rhs = (LinearObjectiveFunction) other;
			return (constantTerm == rhs.constantTerm) && coefficients.equals(rhs.coefficients);

		} catch (ClassCastException ex) {
			// ignore exception
			return false;
		}

	}

	/** {@inheritDoc} */
	@Override
	public int hashCode() {
		return Double.valueOf(constantTerm).hashCode() ^ coefficients.hashCode();
	}

	/**
	 * Serialize the instance.
	 * 
	 * @param oos
	 *            stream where object should be written
	 * @throws IOException
	 *             if object cannot be written to stream
	 */
	private void writeObject(ObjectOutputStream oos) throws IOException {
		oos.defaultWriteObject();
		MatrixUtils.serializeRealVector(coefficients, oos);
	}

	/**
	 * Deserialize the instance.
	 * 
	 * @param ois
	 *            stream from which the object should be read
	 * @throws ClassNotFoundException
	 *             if a class in the stream cannot be found
	 * @throws IOException
	 *             if object cannot be read from the stream
	 */
	private void readObject(ObjectInputStream ois) throws ClassNotFoundException, IOException {
		ois.defaultReadObject();
		MatrixUtils.deserializeRealVector(this, "coefficients", ois);
	}

}
