# Copyright (C) 2003,2004  Michael Creel <michael.creel@uab.es>
#
# 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 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/>.

# Standardizes and normalizes data matrix,
# primarily for use by BFGS

function [zz, scalecoefs] = scale_data(z);

	n = rows(z);
	k = columns(z);

	# Scale data
	s = std(z)';
	test = s != 0;
	s = s + (1 - test); # don't scale if column is a constant (avoid div by zero)
	A = diag(1 ./ s);

	# De-mean all variables except constant, if a constant is present
	test = std(z(:,1)) != 0;
	if test
		bb = zeros(n,k);
		b = zeros(k,1);
	else
		b = -mean(z)';
		test = std(z)' != 0;
		# don't take out mean if the column is a constant, to preserve identification
		b = b .* test;
		b = A*b;
		bb = (diag(b) * ones(k,n))';
	endif
	zz = z*A + bb;
	scalecoefs = {A,b};
endfunction
