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Posted By

vinotht on 06/17/11


Tagged

math


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Calculate SD

 / Published in: Java
 

this simple program will calculate the SD(standard deviation) for the given input. Know more theory about standard deviation @ Standard Deviation Calculator

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  1. public class StandardDeviation{
  2.    public static double mean ( double[] data )
  3.  
  4.       {
  5.  
  6.       double mean = 0;
  7.       final int n = data.length;
  8.       if ( n < 2 )
  9.          return Double.NaN;
  10.       for ( int i=0; i<n; i++ )
  11.          mean += data[i];
  12.       mean /= n;
  13.       double sum = 0;
  14.       for ( int i=0; i<n; i++ )
  15.          {
  16.          final double v = data[i] - mean;
  17.          sum += v * v;
  18.          }
  19.       return Math.sqrt( sum / ( n - 1 ) );
  20.       }
  21.    public static double sd  ( double[] data ){
  22.  
  23.       final int n = data.length;
  24.  
  25.       if ( n < 2 )
  26.          return Double.NaN;
  27.       double avg = data[0];
  28.       double sum = 0;
  29.       for ( int i = 1; i < data.length; i++ )
  30.          {
  31.          double newavg = avg + ( data[i] - avg ) / ( i + 1 );
  32.          sum += ( data[i] - avg ) * ( data [i] -newavg ) ;
  33.          avg = newavg;
  34.          }
  35.       return Math.sqrt( sum / ( n - 1 ) );
  36.       }
  37.    public static void main ( String[] args )
  38.       {
  39.       double[] data = { 10, 100 , 50};
  40.       System.out.println(mean(data));
  41.       System.out.println(sd (data));
  42.       }
  43.    }

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