1 ## Copyright (C) 2012 Rik Wehbring
2 ## Copyright (C) 1995-2012 Kurt Hornik
4 ## This file is part of Octave.
6 ## Octave is free software; you can redistribute it and/or modify it
7 ## under the terms of the GNU General Public License as published by
8 ## the Free Software Foundation; either version 3 of the License, or (at
9 ## your option) any later version.
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14 ## General Public License for more details.
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21 ## @deftypefn {Function File} {} poisspdf (@var{x}, @var{lambda})
22 ## For each element of @var{x}, compute the probability density function
23 ## (PDF) at @var{x} of the Poisson distribution with parameter @var{lambda}.
26 ## Author: KH <Kurt.Hornik@wu-wien.ac.at>
27 ## Description: PDF of the Poisson distribution
29 function pdf = poisspdf (x, lambda)
35 if (!isscalar (lambda))
36 [retval, x, lambda] = common_size (x, lambda);
38 error ("poisspdf: X and LAMBDA must be of common size or scalars");
42 if (iscomplex (x) || iscomplex (lambda))
43 error ("poisspdf: X and LAMBDA must not be complex");
46 if (isa (x, "single") || isa (lambda, "single"))
47 pdf = zeros (size (x), "single");
49 pdf = zeros (size (x));
52 k = isnan (x) | !(lambda > 0);
55 k = (x >= 0) & (x < Inf) & (x == fix (x)) & (lambda > 0);
56 if (isscalar (lambda))
57 pdf(k) = exp (x(k) * log (lambda) - lambda - gammaln (x(k) + 1));
59 pdf(k) = exp (x(k) .* log (lambda(k)) - lambda(k) - gammaln (x(k) + 1));
66 %! x = [-1 0 1 2 Inf];
67 %! y = [0, exp(-1)*[1 1 0.5], 0];
68 %!assert(poisspdf (x, ones(1,5)), y, eps);
69 %!assert(poisspdf (x, 1), y, eps);
70 %!assert(poisspdf (x, [1 0 NaN 1 1]), [y(1) NaN NaN y(4:5)], eps);
71 %!assert(poisspdf ([x, NaN], 1), [y, NaN], eps);
73 %% Test class of input preserved
74 %!assert(poisspdf (single([x, NaN]), 1), single([y, NaN]), eps("single"));
75 %!assert(poisspdf ([x, NaN], single(1)), single([y, NaN]), eps("single"));
77 %% Test input validation
80 %!error poisspdf (1,2,3)
81 %!error poisspdf (ones(3),ones(2))
82 %!error poisspdf (ones(2),ones(3))
83 %!error poisspdf (i, 2)
84 %!error poisspdf (2, i)