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The core of LensKit, providing basic implementations and algorithm support.
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/*
 * LensKit, an open source recommender systems toolkit.
 * Copyright 2010-2016 LensKit Contributors.  See CONTRIBUTORS.md.
 * Work on LensKit has been funded by the National Science Foundation under
 * grants IIS 05-34939, 08-08692, 08-12148, and 10-17697.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */
package org.lenskit.bias;

import it.unimi.dsi.fastutil.longs.Long2DoubleMap;
import it.unimi.dsi.fastutil.longs.Long2DoubleMaps;
import it.unimi.dsi.fastutil.longs.LongSet;
import org.grouplens.grapht.annotation.DefaultProvider;
import org.lenskit.inject.Shareable;

import net.jcip.annotations.Immutable;
import java.io.Serializable;

/**
 * Bias model that only uses a global bias.
 */
@Shareable
@Immutable
@DefaultProvider(GlobalAverageRatingBiasModelProvider.class)
public class GlobalBiasModel implements BiasModel, Serializable {
    private static final long serialVersionUID = 1L;

    private final double intercept;

    /**
     * Construct a new global bias model.
     * @param bias The global bias.
     */
    public GlobalBiasModel(double bias) {
        intercept = bias;
    }

    @Override
    public double getIntercept() {
        return intercept;
    }

    @Override
    public double getUserBias(long user) {
        return 0;
    }

    @Override
    public double getItemBias(long item) {
        return 0;
    }

    @Override
    public Long2DoubleMap getUserBiases(LongSet users) {
        return Long2DoubleMaps.EMPTY_MAP;
    }

    @Override
    public Long2DoubleMap getItemBiases(LongSet items) {
        return Long2DoubleMaps.EMPTY_MAP;
    }

    @Override
    public Long2DoubleMap getUserBiases() {
        return Long2DoubleMaps.EMPTY_MAP;
    }

    @Override
    public Long2DoubleMap getItemBiases() {
        return Long2DoubleMaps.EMPTY_MAP;
    }
}