// Catalano Statistics Library
// The Catalano Framework
//
// Copyright © Diego Catalano, 2012-2016
// diego.catalano at live.com
//
// 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;

/**
 *
 * @author Diego
 */
public class Dirichlet implements IMercerKernel{
    
    private int dimension;

    /**
     * Gets the dimension for the kernel. 
     * @return Dimension.
     */
    public int getDimension() {
        return dimension;
    }

    /**
     * Sets the dimension for the kernel. 
     * @param dimension Dimension.
     */
    public void setDimension(int dimension) {
        this.dimension = dimension;
    }

    /**
     * Constructs a new Dirichlet Kernel
     * @param dimension Dimension of the kernel.
     */
    public Dirichlet(int dimension) {
        this.dimension = dimension;
    }

    @Override
    public double Function(double[] x, double[] y) {
        // Optimization in case x and y are
        // exactly the same object reference.

        double prod = 1;
        for (int i = 0; i < x.length; i++)
        {
            double delta = x[i] - y[i];
            double num = Math.sin((dimension + 0.5) * (delta));
            double den = 2.0 * Math.sin(delta / 2.0);
            prod *= num / den;
        }

        return prod;
    }
}