--- /dev/null
+function [SE,M]=sem(x,DIM, W)
+% SEM calculates the standard error of the mean
+%
+% [SE,M] = SEM(x [, DIM [,W]])
+% calculates the standard error (SE) in dimension DIM
+% the default DIM is the first non-single dimension
+% M returns the mean.
+% Can deal with complex data, too.
+%
+% DIM dimension
+% 1: SEM of columns
+% 2: SEM of rows
+% N: SEM of N-th dimension
+% default or []: first DIMENSION, with more than 1 element
+% W weights to compute weighted mean and s.d. (default: [])
+% if W=[], all weights are 1.
+% number of elements in W must match size(x,DIM)
+%
+% features:
+% - can deal with NaN's (missing values)
+% - weighting of data
+% - dimension argument
+% - compatible to Matlab and Octave
+%
+% see also: SUMSKIPNAN, MEAN, VAR, STD
+
+% This program is free software; you can redistribute it and/or modify
+% it under the terms of the GNU General Public License as published by
+% the Free Software Foundation; either version 3 of the License, or
+% (at your option) any later version.
+%
+% This program is distributed in the hope that it will be useful,
+% but WITHOUT ANY WARRANTY; without even the implied warranty of
+% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+% GNU General Public License for more details.
+%
+% You should have received a copy of the GNU General Public License
+% along with this program; If not, see <http://www.gnu.org/licenses/>.
+
+% Copyright (C) 2000-2003,2008,2009 by Alois Schloegl <alois.schloegl@gmail.com>
+% $Id: sem.m 8223 2011-04-20 09:16:06Z schloegl $
+% This function is part of the NaN-toolbox
+% http://pub.ist.ac.at/~schloegl/matlab/NaN/
+
+
+if nargin>2,
+ [S,N,SSQ] = sumskipnan(x,DIM,W);
+elseif nargin>1,
+ [S,N,SSQ] = sumskipnan(x,DIM);
+else
+ [S,N,SSQ] = sumskipnan(x);
+end
+
+M = S./N;
+SE = (SSQ.*N - real(S).^2 - imag(S).^2)./(N.*N.*(N-1));
+SE(SE<=0) = 0; % prevent negative value caused by round-off error
+SE = sqrt(real(SE));
+