// Catalano Statistics Library
// The Catalano Framework
//
// Copyright © César Souza, 2009-2013
// cesarsouza at gmail.com
//
//    This library is free software; you can redistribute it and/or
//    modify it under the terms of the GNU Lesser General Public
//    License as published by the Free Software Foundation; either
//    version 2.1 of the License, or (at your option) any later version.
//
//    This library is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
//    Lesser General Public License for more details.
//
//    You should have received a copy of the GNU Lesser General Public
//    License along with this library; if not, write to the Free Software
//    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
//

package Catalano.Statistics.Kernels;

/**
 * Power Kernel.
 * Also known as the (Unrectified) Triangular Kernel.
 * @author Diego
 */
public class Power implements IMercerKernel{
    
    private double degree;

    /**
     * Constructs a new Power kernel.
     * @param degree A constant intercept term. Default is 1.
     */
    public Power(double degree){
        this.degree = degree;
    }

    /**
     * Gets the kernel's degree.
     * @return Kernel's degree.
     */
    public double getDegree(){
        return degree;
    }

    /**
     * Sets the kernel's degree.
     * @param degree Kernel's degree.
     */
    public void setDegree(double degree){
        degree = degree;
    }

    /**
     * Linear kernel function.
     * @param x Vector x in input space.
     * @param y Vector y in input space.
     * @return Dot product in feature (kernel) space.
     */
    public double Function(double[] x, double[] y){
        double norm = 0;
        for (int i = 0; i < x.length; i++){
            double d = x[i] - y[i];
            norm += d * d;
        }

        return -Math.pow(norm, degree);
    }
}