modules/ml/src/main/java/org/apache/ignite/ml/math/distances/BrayCurtisDistance.java

/*
 * 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.ignite.ml.math.distances;

import org.apache.ignite.ml.math.exceptions.math.CardinalityException;
import org.apache.ignite.ml.math.primitives.vector.Vector;
import org.apache.ignite.ml.math.util.MatrixUtil;

/**
 * Calculates the Bray Curtis distance between two points.
 *
 * @see <a href="https://en.wikipedia.org/wiki/Bray%E2%80%93Curtis_dissimilarity">
 *   Bray–Curtis dissimilarity</a>
 */
public class BrayCurtisDistance implements DistanceMeasure {
  /** Serializable version identifier. */
  private static final long serialVersionUID = 1771556549784040091L;

  /** {@inheritDoc} */
  @Override public double compute(Vector a, Vector b)
      throws CardinalityException {
    double diff = MatrixUtil.localCopyOf(a).minus(b).kNorm(1);
    double sum = MatrixUtil.localCopyOf(a).plus(b).kNorm(1);

    return diff / sum;
  }

  /** {@inheritDoc} */
  @Override public boolean equals(Object obj) {
    if (this == obj)
      return true;

    return obj != null && getClass() == obj.getClass();
  }

  /** {@inheritDoc} */
  @Override public int hashCode() {
    return getClass().hashCode();
  }

  /** {@inheritDoc} */
  @Override public String toString() {
    return "BrayCurtisDistance{}";
  }
}