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.Configurable;
020import com.oracle.labs.mlrg.olcut.provenance.ConfiguredObjectProvenance;
021import com.oracle.labs.mlrg.olcut.provenance.Provenancable;
022import org.tribuo.math.la.SparseVector;
023
024import java.io.Serializable;
025
026/**
027 * An interface for a Mercer kernel function.
028 * <p>
029 * It's preferable for kernels to override toString.
030 */
031public interface Kernel extends Configurable, Provenancable<ConfiguredObjectProvenance>, Serializable {
032
033    /**
034     * Calculates the similarity between two {@link SparseVector}s.
035     * @param first The first SparseVector.
036     * @param second The second SparseVector.
037     * @return A value between 0 and 1, where 1 is most similar and 0 is least similar.
038     */
039    public double similarity(SparseVector first, SparseVector second);
040
041}