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function [ave, std] = runstats(x) 
%RUNSTATS Generate running ave / std deviation 
% Function RUNSTATS generates a running average  
% and standard deviation of a data set.  The 
% values x must be passed to this function one 
% at a time.  A call to RUNSTATS with the argument 
% 'reset' will reset tue running sums. 
  
% Define variables: 
%   ave      -- Running average 
%   msg      -- Error message 
%   n        -- Number of data values 
%   std      -- Running standard deviation 
%   sum_x    -- Running sum of data values 
%   sum_x2   -- Running sum of data values squared 
%   x        -- Input value 
 
%  Record of revisions: 
%      Date       Programmer          Description of change 
%      ====       ==========          ===================== 
%    12/16/98    S. J. Chapman        Original code 
 
% Declare persistent values 
persistent n            % Number of input values 
persistent sum_x        % Running sum of values 
persistent sum_x2       % Running sum of values squared 
 
% Check for a legal number of input arguments. 
msg = nargchk(1,1,nargin); 
error(msg); 
 
% If the argument is 'reset', reset the running sums. 
if x == 'reset' 
   n = 0; 
   sum_x = 0; 
   sum_x2 = 0; 
else 
   n = n + 1; 
   sum_x = sum_x + x; 
   sum_x2 = sum_x2 + x^2; 
end 
 
% Calculate ave and sd 
if n == 0 
   ave = 0; 
   std = 0; 
elseif n == 1 
   ave = sum_x; 
   std = 0; 
else 
   ave = sum_x / n;  
   std = sqrt((n*sum_x2 - sum_x^2) / (n*(n-1))); 
end