nom.bdezonia.zorbage.algorithm.ApproxVariance Maven / Gradle / Ivy

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/*
 * Zorbage: an algebraic data hierarchy for use in numeric processing.
 *
 * Copyright (c) 2016-2021 Barry DeZonia All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 * 
 * Redistributions of source code must retain the above copyright notice, this list
 * of conditions and the following disclaimer.
 * 
 * Redistributions in binary form must reproduce the above copyright notice, this
 * list of conditions and the following disclaimer in the documentation and/or other
 * materials provided with the distribution.
 * 
 * Neither the name of the  nor the names of its contributors may
 * be used to endorse or promote products derived from this software without specific
 * prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL  BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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 * DAMAGE.
 */
package nom.bdezonia.zorbage.algorithm;

import nom.bdezonia.zorbage.algebra.Addition;
import nom.bdezonia.zorbage.algebra.Algebra;
import nom.bdezonia.zorbage.algebra.Invertible;
import nom.bdezonia.zorbage.algebra.Multiplication;
import nom.bdezonia.zorbage.algebra.Ordered;
import nom.bdezonia.zorbage.algebra.Unity;
import nom.bdezonia.zorbage.datasource.IndexedDataSource;

/**
 * 
 * @author Barry DeZonia
 *
 */
public class ApproxVariance {

	// do not instantiate
	
	private ApproxVariance() {}
	
	/**
	 * ApproxVariance gives an approximate estimate of the variance
	 * of a list of numbers. It is approximate in the sense that adjustments
	 * are made to avoid overall data loss at the expense of absolute
	 * accuracy. If you need absolute accuracy use the {@link Variance}
	 * algorithm using {@link HighPrecisionMember}s to contain the results. 
	 * 
	 * @param alg
	 * @param storage
	 * @param result
	 */
	public static  & Addition & Multiplication & Unity &
								Invertible & Ordered, U>
		void compute(T alg, IndexedDataSource storage, U result)
	{
		long storageSize = storage.size();
		if (storageSize == 0 || storageSize == 1) {
			alg.zero().call(result);
			return;
		}
		U avg = alg.construct();
		U sum = alg.construct();
		U count = alg.construct();
		U one = alg.construct();
		alg.unity().call(one);
		ApproxSumOfSquaredDeviationsWithCount.compute(alg, storage, avg, sum, count);
		alg.subtract().call(count, one, count);
		alg.divide().call(sum, count, result);
	}
}