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diff --git a/octave_packages/m/statistics/distributions/poisspdf.m b/octave_packages/m/statistics/distributions/poisspdf.m
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+## Copyright (C) 2012 Rik Wehbring
+## Copyright (C) 1995-2012 Kurt Hornik
+##
+## This file is part of Octave.
+##
+## Octave 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.
+##
+## Octave 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 Octave; see the file COPYING.  If not, see
+## <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {} poisspdf (@var{x}, @var{lambda})
+## For each element of @var{x}, compute the probability density function
+## (PDF) at @var{x} of the Poisson distribution with parameter @var{lambda}.
+## @end deftypefn
+
+## Author: KH <Kurt.Hornik@wu-wien.ac.at>
+## Description: PDF of the Poisson distribution
+
+function pdf = poisspdf (x, lambda)
+
+  if (nargin != 2)
+    print_usage ();
+  endif
+
+  if (!isscalar (lambda))
+    [retval, x, lambda] = common_size (x, lambda);
+    if (retval > 0)
+      error ("poisspdf: X and LAMBDA must be of common size or scalars");
+    endif
+  endif
+
+  if (iscomplex (x) || iscomplex (lambda))
+    error ("poisspdf: X and LAMBDA must not be complex");
+  endif
+
+  if (isa (x, "single") || isa (lambda, "single"))
+    pdf = zeros (size (x), "single");
+  else
+    pdf = zeros (size (x));
+  endif
+
+  k = isnan (x) | !(lambda > 0);
+  pdf(k) = NaN;
+
+  k = (x >= 0) & (x < Inf) & (x == fix (x)) & (lambda > 0);
+  if (isscalar (lambda))
+    pdf(k) = exp (x(k) * log (lambda) - lambda - gammaln (x(k) + 1));
+  else
+    pdf(k) = exp (x(k) .* log (lambda(k)) - lambda(k) - gammaln (x(k) + 1));
+  endif
+
+endfunction
+
+
+%!shared x,y
+%! x = [-1 0 1 2 Inf];
+%! y = [0, exp(-1)*[1 1 0.5], 0];
+%!assert(poisspdf (x, ones(1,5)), y, eps);
+%!assert(poisspdf (x, 1), y, eps);
+%!assert(poisspdf (x, [1 0 NaN 1 1]), [y(1) NaN NaN y(4:5)], eps);
+%!assert(poisspdf ([x, NaN], 1), [y, NaN], eps);
+
+%% Test class of input preserved
+%!assert(poisspdf (single([x, NaN]), 1), single([y, NaN]), eps("single"));
+%!assert(poisspdf ([x, NaN], single(1)), single([y, NaN]), eps("single"));
+
+%% Test input validation
+%!error poisspdf ()
+%!error poisspdf (1)
+%!error poisspdf (1,2,3)
+%!error poisspdf (ones(3),ones(2))
+%!error poisspdf (ones(2),ones(3))
+%!error poisspdf (i, 2)
+%!error poisspdf (2, i)
+