001/*
002 * Copyright (c) 2015-2020, Oracle and/or its affiliates. All rights reserved.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *     http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.tribuo.math.kernel;
018
019import com.oracle.labs.mlrg.olcut.config.Config;
020import com.oracle.labs.mlrg.olcut.provenance.ConfiguredObjectProvenance;
021import com.oracle.labs.mlrg.olcut.provenance.impl.ConfiguredObjectProvenanceImpl;
022import org.tribuo.math.la.SparseVector;
023
024/**
025 * A Radial Basis Function (RBF) kernel, exp(-gamma*|u-v|^2).
026 */
027public class RBF implements Kernel {
028    private static final long serialVersionUID = 1L;
029
030    @Config(mandatory = true,description="Kernel output = exp(-gamma*|u-v|^2).")
031    private double gamma;
032
033    /**
034     * For olcut.
035     */
036    private RBF() {}
037
038    /**
039     * A Radial Basis Function (RBF) kernel, exp(-gamma*|u-v|^2).
040     * @param gamma The length scale of the gaussian.
041     */
042    public RBF(double gamma) {
043        this.gamma = gamma;
044    }
045
046    @Override
047    public double similarity(SparseVector a, SparseVector b) {
048        return Math.exp(-gamma * Math.pow(a.subtract(b).twoNorm(),2.0));
049    }
050
051    @Override
052    public String toString() {
053        return "RBF(gamma="+gamma+")";
054    }
055
056    @Override
057    public ConfiguredObjectProvenance getProvenance() {
058        return new ConfiguredObjectProvenanceImpl(this,"Kernel");
059    }
060}