/*
* Apache License
* Version 2.0, January 2004
* http://www.apache.org/licenses/
*
* Copyright 2013 Aurelian Tutuianu
* Copyright 2014 Aurelian Tutuianu
* Copyright 2015 Aurelian Tutuianu
* Copyright 2016 Aurelian Tutuianu
*
* Licensed 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 rapaio.ml.classifier.svm.kernel;
import rapaio.data.Frame;
import rapaio.sys.WS;
/**
* The Generalized T-Student Kernel has been proven to be a
* Mercel Kernel, thus having a positive semi-definite Kernel
* matrix (Boughorbel, 2004).
* It is given by:
* <p>
* k(x,y) = \frac{1}{1 + \lVert x-y \rVert ^d}
* <p>
* Created by <a href="mailto:padreati@yahoo.com">Aurelian Tutuianu</a> at 1/21/15.
*/
public class GeneralizedStudentTKernel extends AbstractKernel {
private static final long serialVersionUID = -1302773223473974349L;
private final double degree;
public GeneralizedStudentTKernel(double degree) {
this.degree = degree;
}
@Override
public double eval(Frame df1, int row1, Frame df2, int row2) {
double dot = deltaDotProd(df1, row1, df2, row2);
return 1.0 / (1.0 + Math.pow(dot, degree));
}
@Override
public Kernel newInstance() {
return new GeneralizedStudentTKernel(degree);
}
@Override
public String name() {
return "GeneralizedStudent(degree=" + WS.formatFlex(degree) + ")";
}
}