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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13 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 ## General Public License for more details.
16 ## You should have received a copy of the GNU General Public License
17 ## along with Octave; see the file COPYING. If not, see
18 ## <http://www.gnu.org/licenses/>.
21 ## @deftypefn {Function File} {} exppdf (@var{x}, @var{lambda})
22 ## For each element of @var{x}, compute the probability density function
23 ## (PDF) at @var{x} of the exponential distribution with mean @var{lambda}.
26 ## Author: KH <Kurt.Hornik@wu-wien.ac.at>
27 ## Description: PDF of the exponential distribution
29 function pdf = exppdf (x, lambda)
35 if (!isscalar (lambda))
36 [retval, x, lambda] = common_size (x, lambda);
38 error ("exppdf: X and LAMBDA must be of common size or scalars");
42 if (iscomplex (x) || iscomplex (lambda))
43 error ("exppdf: 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) & (lambda > 0);
57 pdf(k) = exp (- x(k) / lambda) / lambda;
59 pdf(k) = exp (- x(k) ./ lambda(k)) ./ lambda(k);
66 %! x = [-1 0 0.5 1 Inf];
67 %! y = gampdf (x, 1, 2);
68 %!assert(exppdf (x, 2*ones(1,5)), y);
69 %!assert(exppdf (x, 2*[1 0 NaN 1 1]), [y(1) NaN NaN y(4:5)]);
70 %!assert(exppdf ([x, NaN], 2), [y, NaN]);
72 %% Test class of input preserved
73 %!assert(exppdf (single([x, NaN]), 2), single([y, NaN]));
74 %!assert(exppdf ([x, NaN], single(2)), single([y, NaN]));
76 %% Test input validation
79 %!error exppdf (1,2,3)
80 %!error exppdf (ones(3),ones(2))
81 %!error exppdf (ones(2),ones(3))