You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: issq.m
    path of file: ./repos/CBIG/external_packages/SD/SDv1.5.1-svn593/SphericalDemons
    
    the code of the file until where you have to start completion: function [m,ssq] = issq(x,n,m0,ssq0)
% Increment the mean and the sum of squares after a new
% observation is included in the sample.
% To obtain the variance, divide the ssq by n or by n-1.
%
% Usage:
% [m,ssq] = issq(x,n,m0,ssq0)
%
% Inputs:
% x    = New observation
% n    = Observation sequential number (n > 1)
% m0   = Previous mean
% ssq0 = Previous sum of squares
%
% Outputs:
% m    = Updated mean
% ssq  = Updated sum of squares
%
% Reference:
% * Welford, B.P. Note on a method for calculating corrected sums of
%   squares and products. Technometrics (1962) 4(3):419-20

    
function [m,ssq] = issq(x,n,m0,ssq0)
% Increment the mean and the sum of squares after a new
% observation is included in the sample.
% To obtain the variance, divide the ssq by n or by n-1.
%
% Usage:
% [m,ssq] = issq(x,n,m0,ssq0)
%
% Inputs:
% x    = New observation
% n    = Observation sequential number (n > 1)
% m0   = Previous mean
% ssq0 = Previous sum of squares
%
% Outputs:
% m    = Updated mean
% ssq  = Updated sum of squares
%
% Reference:
% * Welford, B.P. Note on a method for calculating corrected sums of
%   squares and products. Technometrics (1962) 4(3):419-20
% 
% _____________________________________
% Anderson M. Winkler
% Yale University / Institute of Living
% Mar/2011

% Accept arguments
if nargin < 3,
    error('Insufficient arguments.')

elseif n <= 1 || round(n) ~= n,
    error('N has to be integer and > 1.')

end