Calculate Variance: the square of the standard deviation in Java

/*  w  w  w.ja v  a 2  s  .  c  o  m*/
/**
 * <p>Static methods for doing useful math</p><hr>
 *
 * @author  : $Author: brian $
 * @version : $Revision: 1.1 $
 *
 * <hr><p><font size="-1" color="#336699"><a href="http://www.mbari.org">
 * The Monterey Bay Aquarium Research Institute (MBARI)</a> provides this
 * documentation and code &quot;as is&quot;, with no warranty, express or
 * implied, of its quality or consistency. It is provided without support and
 * without obligation on the part of MBARI to assist in its use, correction,
 * modification, or enhancement. This information should not be published or
 * distributed to third parties without specific written permission from
 * MBARI.</font></p><br>
 *
 * <font size="-1" color="#336699">Copyright 2002 MBARI.<br>
 * MBARI Proprietary Information. All rights reserved.</font><br><hr><br>
 *
 */
import java.util.Arrays;


/**
 * <p>Static methods for doing useful math</p><hr>
 *
 * @author  : $Author: brian $
 * @version : $Revision: 1.1 $
 *
 * <hr><p><font size="-1" color="#336699"><a href="http://www.mbari.org">
 * The Monterey Bay Aquarium Research Institute (MBARI)</a> provides this
 * documentation and code &quot;as is&quot;, with no warranty, express or
 * implied, of its quality or consistency. It is provided without support and
 * without obligation on the part of MBARI to assist in its use, correction,
 * modification, or enhancement. This information should not be published or
 * distributed to third parties without specific written permission from
 * MBARI.</font></p><br>
 *
 * <font size="-1" color="#336699">Copyright 2002 MBARI.<br>
 * MBARI Proprietary Information. All rights reserved.</font><br><hr><br>
 *
 */

public class Main {
   public static void main(String[] argv){
         System.out.println(variance(new double[]{1.2,1.3,1.4,1.5,1.4}));
   }
            
    /**
     * Variance: the square of the standard deviation. A measure of the degree
     * of spread among a set of values; a measure of the tendency of individual
     * values to vary from the mean value.
     *
     * @param values
     * @return
     */
    public static double variance(double[] values) {
        double std = standardDeviation(values);
        return std * std;
    }
    /**
     * Standard deviation is a statistical measure of spread or variability.The
     * standard deviation is the root mean square (RMS) deviation of the values
     * from their arithmetic mean.
     *
     * <b>standardDeviation</b> normalizes values by (N-1), where N is the sample size.  This is the
     * sqrt of an unbiased estimator of the variance of the population from
     * which X is drawn, as long as X consists of independent, identically
     * distributed samples.
     *
     * @param values
     * @return
     */
    public static strictfp double standardDeviation(double[] values) {
        double mean = mean(values);
        double dv = 0D;
        for (double d : values) {
            double dm = d - mean;
            dv += dm * dm;
        }
        return Math.sqrt(dv / (values.length - 1));
//        double[] deviation = deviationFromMean(values);
//        double s = 0D;
//        for (double d : deviation) {
//            s += (d * d);
//        }
//        return Math.sqrt(s / values.length - 1);
    }

    /**
     * Calculate the mean of an array of values
     *
     * @param values The values to calculate
     * @return The mean of the values
     */
    public static strictfp double mean(double[] values) {
        return sum(values) / values.length;
    }
    /**
     * Sum up all the values in an array
     *
     * @param values an array of values
     * @return The sum of all values in the Array
     */
    public static strictfp double sum(double[] values) {
        if (values == null || values.length == 0) {
            throw new IllegalArgumentException("The data array either is null or does not contain any data.");
        }
        else {
            double sum = 0;
            for (int i = 0; i < values.length; i++) {
                sum += values[i];
            }
            return sum;
        }
    }
}