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A Java's Collaborative Filtering library to carry out experiments in research of Collaborative Filtering based Recommender Systems. The library has been designed from researchers to researchers.
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.math3.geometry.partitioning;

import org.apache.commons.math3.geometry.Space;

/** This interface represents the remaining parts of an hyperplane after
 * other parts have been chopped off.

 * sub-hyperplanes are obtained when parts of an {@link
 * Hyperplane hyperplane} are chopped off by other hyperplanes that
 * intersect it. The remaining part is a convex region. Such objects
 * appear in {@link BSPTree BSP trees} as the intersection of a cut
 * hyperplane with the convex region which it splits, the chopping
 * hyperplanes are the cut hyperplanes closer to the tree root.

 * 
 * Note that this interface is not intended to be implemented
 * by Apache Commons Math users, it is only intended to be implemented
 * within the library itself. New methods may be added even for minor
 * versions, which breaks compatibility for external implementations.
 * 

 * @param  Type of the embedding space.

 * @since 3.0
 */
public interface SubHyperplane {

    /** Copy the instance.
     * The instance created is completely independent of the original
     * one. A deep copy is used, none of the underlying objects are
     * shared (except for the nodes attributes and immutable
     * objects).
     * @return a new sub-hyperplane, copy of the instance
     */
    SubHyperplane copySelf();

    /** Get the underlying hyperplane.
     * @return underlying hyperplane
     */
    Hyperplane getHyperplane();

    /** Check if the instance is empty.
     * @return true if the instance is empty
     */
    boolean isEmpty();

    /** Get the size of the instance.
     * @return the size of the instance (this is a length in 1D, an area
     * in 2D, a volume in 3D ...)
     */
    double getSize();

    /** Compute the relative position of the instance with respect
     * to an hyperplane.
     * @param hyperplane hyperplane to check instance against
     * @return one of {@link Side#PLUS}, {@link Side#MINUS}, {@link Side#BOTH},
     * {@link Side#HYPER}
     * @deprecated as of 3.6, replaced with {@link #split(Hyperplane)}.{@link SplitSubHyperplane#getSide()}
     */
    @Deprecated
    Side side(Hyperplane hyperplane);

    /** Split the instance in two parts by an hyperplane.
     * @param hyperplane splitting hyperplane
     * @return an object containing both the part of the instance
     * on the plus side of the hyperplane and the part of the
     * instance on the minus side of the hyperplane
     */
    SplitSubHyperplane split(Hyperplane hyperplane);

    /** Compute the union of the instance and another sub-hyperplane.
     * @param other other sub-hyperplane to union (must be in the
     * same hyperplane as the instance)
     * @return a new sub-hyperplane, union of the instance and other
     */
    SubHyperplane reunite(SubHyperplane other);

    /** Class holding the results of the {@link #split split} method.
     * @param  Type of the embedding space.
     */
    class SplitSubHyperplane {

        /** Part of the sub-hyperplane on the plus side of the splitting hyperplane. */
        private final SubHyperplane plus;

        /** Part of the sub-hyperplane on the minus side of the splitting hyperplane. */
        private final SubHyperplane minus;

        /** Build a SplitSubHyperplane from its parts.
         * @param plus part of the sub-hyperplane on the plus side of the
         * splitting hyperplane
         * @param minus part of the sub-hyperplane on the minus side of the
         * splitting hyperplane
         */
        public SplitSubHyperplane(final SubHyperplane plus,
                                  final SubHyperplane minus) {
            this.plus  = plus;
            this.minus = minus;
        }

        /** Get the part of the sub-hyperplane on the plus side of the splitting hyperplane.
         * @return part of the sub-hyperplane on the plus side of the splitting hyperplane
         */
        public SubHyperplane getPlus() {
            return plus;
        }

        /** Get the part of the sub-hyperplane on the minus side of the splitting hyperplane.
         * @return part of the sub-hyperplane on the minus side of the splitting hyperplane
         */
        public SubHyperplane getMinus() {
            return minus;
        }

        /** Get the side of the split sub-hyperplane with respect to its splitter.
         * @return {@link Side#PLUS} if only {@link #getPlus()} is neither null nor empty,
         * {@link Side#MINUS} if only {@link #getMinus()} is neither null nor empty,
         * {@link Side#BOTH} if both {@link #getPlus()} and {@link #getMinus()}
         * are neither null nor empty or {@link Side#HYPER} if both {@link #getPlus()} and
         * {@link #getMinus()} are either null or empty
         * @since 3.6
         */
        public Side getSide() {
            if (plus != null && !plus.isEmpty()) {
                if (minus != null && !minus.isEmpty()) {
                    return Side.BOTH;
                } else {
                    return Side.PLUS;
                }
            } else if (minus != null && !minus.isEmpty()) {
                return Side.MINUS;
            } else {
                return Side.HYPER;
            }
        }

    }

}