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} {} expcdf (@var{x}, @var{lambda})
22 ## For each element of @var{x}, compute the cumulative distribution
23 ## function (CDF) at @var{x} of the exponential distribution with
26 ## The arguments can be of common size or scalars.
29 ## Author: KH <Kurt.Hornik@wu-wien.ac.at>
30 ## Description: CDF of the exponential distribution
32 function cdf = expcdf (x, lambda)
38 if (!isscalar (lambda))
39 [retval, x, lambda] = common_size (x, lambda);
41 error ("expcdf: X and LAMBDA must be of common size or scalars");
45 if (iscomplex (x) || iscomplex (lambda))
46 error ("expcdf: X and LAMBDA must not be complex");
49 if (isa (x, "single") || isa (lambda, "single"))
50 cdf = zeros (size (x), "single");
52 cdf = zeros (size (x));
55 k = isnan (x) | !(lambda > 0);
58 k = (x == Inf) & (lambda > 0);
61 k = (x > 0) & (x < Inf) & (lambda > 0);
63 cdf(k) = 1 - exp (- x(k) / lambda);
65 cdf(k) = 1 - exp (- x(k) ./ lambda(k));
72 %! x = [-1 0 0.5 1 Inf];
73 %! y = [0, 1 - exp(-x(2:end)/2)];
74 %!assert(expcdf (x, 2*ones(1,5)), y);
75 %!assert(expcdf (x, 2), y);
76 %!assert(expcdf (x, 2*[1 0 NaN 1 1]), [y(1) NaN NaN y(4:5)]);
78 %% Test class of input preserved
79 %!assert(expcdf ([x, NaN], 2), [y, NaN]);
80 %!assert(expcdf (single([x, NaN]), 2), single([y, NaN]));
81 %!assert(expcdf ([x, NaN], single(2)), single([y, NaN]));
83 %% Test input validation
86 %!error expcdf (1,2,3)
87 %!error expcdf (ones(3),ones(2))
88 %!error expcdf (ones(2),ones(3))