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 sigmoid kernel, tanh(gamma*u.dot(v) + intercept).
026 */
027public class Sigmoid 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 intercept to add to the dot product.")
034    private double intercept;
035
036    /**
037     * For olcut.
038     */
039    private Sigmoid() {}
040
041    /**
042     * A sigmoid kernel, tanh(gamma*u.dot(v) + intercept).
043     * @param gamma A scalar coefficient.
044     * @param intercept An additive coefficient.
045     */
046    public Sigmoid(double gamma, double intercept) {
047        this.gamma = gamma;
048        this.intercept = intercept;
049    }
050
051    @Override
052    public double similarity(SparseVector a, SparseVector b) {
053        return Math.tanh(gamma * a.dot(b) + intercept);
054    }
055
056    @Override
057    public String toString() {
058        return "Sigmoid(gamma="+gamma+",intercept="+intercept+")";
059    }
060
061    @Override
062    public ConfiguredObjectProvenance getProvenance() {
063        return new ConfiguredObjectProvenanceImpl(this,"Kernel");
064    }
065}