content: /*******************************************************************************
   * Copyright (c) 2010 Haifeng Li
   *   
   * Licensed 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 smile.math.distance;
  
  /**
   * A metric function defines a distance between elements of a set. Besides
   * non-negativity, isolation, and symmetry, it also has to satisfy triangular
   * inequality.
   * <ul>
   * <li> non-negativity: d(x, y) &ge; 0
   * <li> isolation: d(x, y) = 0 if and only if x = y
   * <li> symmetry: d(x, y) = d(x, y)
   * <li> triangular inequality: d(x, y) + d(y, z) &ge; d(x, z).
   * </ul>.
   *
   * @author Haifeng Li
   */
  public interface Metric<T> extends Distance<T> {
  
  }
  