Generic univariate summary statistic objects.
        UnivariateStatistic API Usage Examples:
        UnivariateStatistic:
        /* evaluation approach */
 double[] values = new double[] { 1, 2,
            3, 4, 5 };
 UnivariateStatistic stat
            = new Mean();
 System.out.println("mean = " + stat.evaluate(values));
 
        StorelessUnivariateStatistic:
        /* incremental approach */
 double[] values = new double[] { 1, 2,
            3, 4, 5 };
 
            StorelessUnivariateStatistic stat = new Mean();
            System.out.println("mean before adding a value is NaN = " + stat.getResult());
 for (int i = 0;
            i < values.length; i++) {
     stat.increment(values[i]);
    
            System.out.println("current mean = " + 
            stat2.getResult());
 }
 
            stat.clear();
 System.out.println("mean after clear is NaN = "
            + stat.getResult());