www.pudn.com > CryptoPhone-src-031122.zip > variance.c

/* Copyright 2001,2002,2003 NAH6 
 * All Rights Reserved 
 * 
 * Parts Copyright DoD, Parts Copyright Starium 
 * 
 */ 
/*************************************************************************** 
 
 ROUTINE 
               variance 
 
 FUNCTION 
                 
               calculates variance of the input array 
 
 SYNOPSIS 
               subroutine variance(arr,no,var,avg) 
 
   formal  
 
                       data    I/O 
       name            type    type    function 
       ------------------------------------------------------------------- 
       arr		real	i	input data array 
       no		int	i	number of elements in array 
       var		real	o	variance 
       avg		real	o	average 
 
 
**************************************************************************/ 
#include "variance.h" 
 
void variance( 
float 	*arr, 
int 	no, 
float 	*var, 
float 	*avg) 
{ int i; 
  float sum = 0.0, sum2 = 0.0, tavg; 
 
  for (i=0; i < no; i++) 
    sum += arr[i]; 
  tavg = sum / (float) no; 
 
  for (i = 0; i < no; i++) 
    sum2 += (tavg - arr[i]) * (tavg - arr[i]); 
 
  *avg = tavg; 
  *var = sum2 / (float) (no-1); 
}