/**
* Copyright (C) 2009 - present by OpenGamma Inc. and the OpenGamma group of companies
*
* Please see distribution for license.
*/
package com.opengamma.analytics.math.statistics.descriptive;
import org.apache.commons.lang.Validate;
import com.opengamma.analytics.math.function.Function1D;
/**
* Calculates the geometric mean of a series of data.
* <p>
* The geometric mean $\mu$ of a series of elements $x_1, x_2, \dots, x_n$ is given by:
* $$
* \begin{align*}
* \mu = \left({\prod\limits_{i=1}^n x_i}\right)^{\frac{1}{n}}
* \end{align*}
* $$
*
*/
public class GeometricMeanCalculator extends Function1D<double[], Double> {
/**
* @param x The array of data, not null or empty
* @return The geometric mean
*/
@Override
public Double evaluate(final double[] x) {
Validate.notNull(x, "x");
Validate.isTrue(x.length > 0, "x cannot be empty");
final int n = x.length;
double mult = x[0];
for (int i = 1; i < n; i++) {
mult *= x[i];
}
return Math.pow(mult, 1. / n);
}
}