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 polynomial kernel, (gamma*u.dot(v) + intercept)^degree.
026 */
027public class Polynomial implements Kernel {
028    private static final long serialVersionUID = 1L;
029
030    @Config(mandatory = true,description="Coefficient to multiply the dot product by.")
031    private double gamma;
032
033    @Config(mandatory = true,description="Scalar to add to the dot product.")
034    private double intercept;
035
036    @Config(mandatory = true,description="Degree of the polynomial.")
037    private double degree;
038
039    /**
040     * For olcut.
041     */
042    private Polynomial() {}
043
044    /**
045     * A polynomial kernel, (gamma*u.dot(v) + intercept)^degree.
046     * @param gamma The scalar coefficient.
047     * @param intercept An additive coefficient.
048     * @param degree The degree of the polynomial.
049     */
050    public Polynomial(double gamma, double intercept, double degree) {
051        this.gamma = gamma;
052        this.intercept = intercept;
053        this.degree = degree;
054    }
055
056    @Override
057    public double similarity(SparseVector a, SparseVector b) {
058        return Math.pow(gamma * a.dot(b) + intercept, degree);
059    }
060
061    @Override
062    public String toString() {
063        return "Polynomial(gamma="+gamma+",intercept="+intercept+",degree="+degree+")";
064    }
065
066    @Override
067    public ConfiguredObjectProvenance getProvenance() {
068        return new ConfiguredObjectProvenanceImpl(this,"Kernel");
069    }
070}