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.classification.sgd;
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 com.oracle.labs.mlrg.olcut.util.Pair;
023import org.tribuo.math.la.SGDVector;
024import org.tribuo.math.util.VectorNormalizer;
025
026/**
027 * An interface for single label prediction objectives.
028 * <p>
029 * An objective knows if it generates a probabilistic model or not,
030 * and what kind of normalization needs to be applied to produce probability values.
031 */
032public interface LabelObjective extends Configurable, Provenancable<ConfiguredObjectProvenance> {
033
034    /**
035     * Scores a prediction, returning the loss and a vector of per label gradients.
036     * @param truth The true label id.
037     * @param prediction The prediction for each label id.
038     * @return The score and per label gradient.
039     */
040    public Pair<Double,SGDVector> valueAndGradient(int truth, SGDVector prediction);
041
042    /**
043     * Generates a new {@link VectorNormalizer} which normalizes the predictions into [0,1].
044     * @return The vector normalizer for this objective.
045     */
046    public VectorNormalizer getNormalizer();
047
048    /**
049     * Does the objective function score probabilities or not?
050     * @return boolean.
051     */
052    public boolean isProbabilistic();
053
054}