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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.
+
+## Called by logistic_regression.  Calculates derivates of the
+## log-likelihood for ordinal logistic regression model.
+  
+## Author:  Gordon K. Smyth <gks@maths.uq.oz.au>
+## Adapted-By:  KH <Kurt.Hornik@ci.tuwien.ac.at>
+## Description:  Derivates of log-likelihood in logistic regression
+
+function [dl, d2l] ...
+      = logistic_regression_derivatives (x, z, z1, g, g1, p)
+  
+  ## first derivative
+  v = g .* (1 - g) ./ p; v1 = g1 .* (1 - g1) ./ p;
+  dlogp = [dmult (v, z) - dmult (v1, z1) dmult (v - v1, x)];
+  dl = sum (dlogp)';
+
+  ## second derivative
+  w = v .* (1 - 2 * g); w1 = v1 .* (1 - 2 * g1);
+  d2l = [z x]' * dmult (w, [z x]) - [z1 x]' * dmult (w1, [z1 x]) ...
+      - dlogp' * dlogp;
+  
+endfunction
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