1## Copyright (C) 2012 Rik Wehbring
2## Copyright (C) 2007-2016 David Bateman
3##
4## This program is free software: you can redistribute it and/or
5## modify it under the terms of the GNU General Public License as
6## published by the Free Software Foundation, either version 3 of the
7## License, or (at your option) any later version.
8##
9## This program is distributed in the hope that it will be useful, but
10## WITHOUT ANY WARRANTY; without even the implied warranty of
11## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
12## General Public License for more details.
13##
14## You should have received a copy of the GNU General Public License
15## along with this program; see the file COPYING.  If not, see
16## <http://www.gnu.org/licenses/>.
17
18## -*- texinfo -*-
19## @deftypefn {} {} unidpdf (@var{x}, @var{n})
20## For each element of @var{x}, compute the probability density function (PDF)
21## at @var{x} of a discrete uniform distribution which assumes
22## the integer values 1--@var{n} with equal probability.
23##
24## Warning: The underlying implementation uses the double class and will only
25## be accurate for @var{n} < @code{flintmax} (@w{@math{2^{53}}} on
26## IEEE 754 compatible systems).
27## @end deftypefn
28
29function pdf = unidpdf (x, n)
30
31  if (nargin != 2)
32    print_usage ();
33  endif
34
35  if (! isscalar (n))
36    [retval, x, n] = common_size (x, n);
37    if (retval > 0)
38      error ("unidpdf: X and N must be of common size or scalars");
39    endif
40  endif
41
42  if (iscomplex (x) || iscomplex (n))
43    error ("unidpdf: X and N must not be complex");
44  endif
45
46  if (isa (x, "single") || isa (n, "single"))
47    pdf = zeros (size (x), "single");
48  else
49    pdf = zeros (size (x));
50  endif
51
52  k = isnan (x) | ! (n > 0 & n == fix (n));
53  pdf(k) = NaN;
54
55  k = ! k & (x >= 1) & (x <= n) & (x == fix (x));
56  if (isscalar (n))
57    pdf(k) = 1 / n;
58  else
59    pdf(k) = 1 ./ n(k);
60  endif
61
62endfunction
63
64
65%!shared x,y
66%! x = [-1 0 1 2 10 11];
67%! y = [0 0 0.1 0.1 0.1 0];
68%!assert (unidpdf (x, 10*ones (1,6)), y)
69%!assert (unidpdf (x, 10), y)
70%!assert (unidpdf (x, 10*[0 NaN 1 1 1 1]), [NaN NaN y(3:6)])
71%!assert (unidpdf ([x, NaN], 10), [y, NaN])
72
73## Test class of input preserved
74%!assert (unidpdf (single ([x, NaN]), 10), single ([y, NaN]))
75%!assert (unidpdf ([x, NaN], single (10)), single ([y, NaN]))
76
77## Test input validation
78%!error unidpdf ()
79%!error unidpdf (1)
80%!error unidpdf (1,2,3)
81%!error unidpdf (ones (3), ones (2))
82%!error unidpdf (ones (2), ones (3))
83%!error unidpdf (i, 2)
84%!error unidpdf (2, i)
85