SigmoidalKernel.java

/*
 * MIT License
 *
 * Copyright (c) 2009-2016 Ignacio Calderon <https://github.com/kronenthaler>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package libai.common.kernels;

import libai.common.matrix.Matrix;

/**
 * Sigmoid Kernel. Follows the form: K(x,y) = tanh(a * xy + b), where a &amp; b are
 * parameters of this kernel.
 *
 * @author kronenthaler
 */
public class SigmoidalKernel implements Kernel {

    private static final long serialVersionUID = 5132845207274843125L;

    private final double a;
    private final double b;

    public SigmoidalKernel(double a, double b) {
        this.a = a;
        this.b = b;
    }

    @Override
    public double eval(Matrix A, Matrix B) {
        double dotProduct = A.dotProduct(B);
        return Math.tanh(a * dotProduct + b);
    }
}