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## Copyright (C) 1995, 1996, 1997 Kurt Hornik
##
## 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 2, 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 file. If not, write to the Free Software Foundation,
## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
## usage: studentize (x)
##
## If x is a vector, subtract its mean and divide by its standard
## deviation.
##
## If x is a matrix, do the above for each column.
## Author: KH <Kurt.Hornik@ci.tuwien.ac.at>
## Description: Subtract mean and divide by standard deviation
function t = studentize (x)
if (nargin != 1)
usage ("studentize (x)");
endif
if is_vector (x)
if (std (x) == 0)
t = zeros (size (x));
else
t = (x - mean (x)) / std (x);
endif
elseif is_matrix (x)
l = ones (rows (x), 1);
t = x - l * mean (x);
t = t ./ (l * max ([std (t); !any (t)]));
else
error ("studentize: x must be a vector or a matrix.");
endif
endfunction
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