--- /dev/null
+# Copyright (C) 2005 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/>.
+
+# Example likelihood function (Poisson for count data) with score
+
+function [log_density, score] = poisson(theta, data, otherargs)
+ y = data(:,1);
+ x = data(:,2:columns(data));
+ lambda = exp(x*theta);
+ log_density = -lambda + y .* (x*theta) - lgamma(y+1);
+ score = diag (y - lambda) * x;
+ if (otherargs{1} == 1) score = "na"; endif # provide analytic score or not?
+endfunction