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/*******************************************************************************
 * 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.
 * 
 *  non-negativity: d(x, y) ≥ 0
 * 
 isolation: d(x, y) = 0 if and only if x = y
 * 
 symmetry: d(x, y) = d(x, y)
 * 
 triangular inequality: d(x, y) + d(y, z) ≥ d(x, z).
 * .
 *
 * @author Haifeng Li
 */
public interface Metric extends Distance {

}