org.simmetrics.Distance Maven / Gradle / Ivy
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* #%L
* Simmetrics Core
* %%
* Copyright (C) 2014 - 2015 Simmetrics Authors
* %%
* 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
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
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* #L%
*/
package org.simmetrics;
/**
* Measures the unnormalized dissimilarity between two arbitrary objects of the
* same type. The measurement results in a non-negative value. A value of zero
* indicates that the objects are similar.
*
* The distance measure should be consistent with equals such that
* {@code a.equals(b) => distance(a,b) == 0.0}.
*
* The distance measure should be reflexive such that
* {@code distance(a,a) == 0.0}.
*
* The distance measure should be symmetric such that
* {@code distance(a,b) == distance(b,a)}.
*
* The distance measure may be transitive such that
* {@code distance(a, c) ≤ distance(a, b) + distance(b, c)}
*
* The distance measure may satisfy the coincidence axiom such that
* {@code compare(a, b) = 0 if and only if a.equals(b)}
*
* Implementations may not modify the arguments. Arguments should be treated as
* if they were unmodifiable.
*
* @see Wikipedia -
* Metric
*
* @param
* type of the elements compared
*
*/
public interface Distance {
/**
* Measures the distance between a and b. The measurement results in a
* non-negative value. A value of {@code 0.0} indicates that {@code a} and
* {@code b} are similar.
*
* @param a
* object a to compare
* @param b
* object b to compare
* @return a non-negative value
* @throws NullPointerException
* when either a or b is null
*/
float distance(T a, T b);
}