## Copyright (C) 2012 Rik Wehbring
## Copyright (C) 1995-2016 Kurt Hornik
## Copyright (C) 2023 Andreas Bertsatos <abertsatos@biol.uoa.gr>
##
## This file is part of the statistics package for GNU Octave.
##
## This program 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.
##
## This program 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
## this program; if not, see <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn  {statistics} {@var{r} =} geornd (@var{ps})
## @deftypefnx {statistics} {@var{r} =} geornd (@var{ps}, @var{rows})
## @deftypefnx {statistics} {@var{r} =} geornd (@var{ps}, @var{rows}, @var{cols}, @dots{})
## @deftypefnx {statistics} {@var{r} =} geornd (@var{ps}, [@var{sz}])
##
## Random arrays from the geometric distribution.
##
## @code{@var{r} = geornd (@var{ps})} returns an array of random numbers chosen
## from the Birnbaum-Saunders distribution with probability of success parameter
## @var{ps}.  The size of @var{r} is the size of @var{ps}.
##
## When called with a single size argument, @code{geornd} returns a square
## matrix with the dimension specified.  When called with more than one scalar
## argument, the first two arguments are taken as the number of rows and columns
## and any further arguments specify additional matrix dimensions.  The size may
## also be specified with a row vector of dimensions, @var{sz}.
##
## The geometric distribution models the number of failures (@var{x}) of a
## Bernoulli trial with probability @var{ps} before the first success.
##
## Further information about the geometric distribution can be found at
## @url{https://en.wikipedia.org/wiki/Geometric_distribution}
##
## @seealso{geocdf, geoinv, geopdf, geofit, geostat}
## @end deftypefn

function r = geornd (ps, varargin)

  ## Check for valid number of input arguments
  if (nargin < 1)
    error ("geornd: function called with too few input arguments.");
  endif

  ## Check for PS being reals
  if (iscomplex (ps))
    error ("geornd: PS must not be complex.");
  endif

  ## Parse and check SIZE arguments
  if (nargin == 1)
    sz = size (ps);
  elseif (nargin == 2)
    if (isscalar (varargin{1}) && varargin{1} == fix (varargin{1}))
      sz = [varargin{1}, varargin{1}];
    elseif (isrow (varargin{1}) && all (varargin{1} == fix (varargin{1})))
      sz = varargin{1};
    elseif (isempty (varargin{1}))
      r = [];
      return;
    else
      error (strcat ("geornd: SZ must be a scalar or a row vector", ...
                     " of integers."));
    endif
  elseif (nargin > 2)
    notint = cellfun (@(x) (! isscalar (x) || x != fix (x)), varargin);
    if (any (notint))
      error ("geornd: dimensions must be integers.");
    endif
    sz = [varargin{:}];
  endif

  ## Negative dimensions are treated as zero, as in core Octave and MATLAB
  sz = max (sz, 0);

  ## Check that parameter match requested dimensions in size
  ## Use 'size (ones (sz))' to ignore any trailing singleton dimensions in SZ
  if (! isscalar (ps) && ! isequal (size (ps), size (ones (sz))))
    error ("geornd: PS must be scalar or of size SZ.");
  endif

  ## Check for class type
  if (isa (ps, 'single'))
    cls = 'single';
  else
    cls = 'double';
  endif

  ## Generate random sample from geometric distribution
  if (isscalar (ps))
    if (ps > 0 && ps < 1);
      r = floor (- rande (sz, cls) ./ log (1 - ps));
    elseif (ps == 0)
      r = Inf (sz, cls);
    elseif (ps == 1)
      r = zeros (sz, cls);
    elseif (ps < 0 || ps > 1)
      r = NaN (sz, cls);
    endif
  else
    r = floor (- rande (sz, cls) ./ log (1 - ps));

    k = ! (ps >= 0) | ! (ps <= 1);
    r(k) = NaN;

    k = (ps == 0);
    r(k) = Inf;
  endif

endfunction

## Test output
%!assert_equal (size (geornd (0.5)), [1, 1])
%!assert_equal (size (geornd (0.5*ones (2,1))), [2, 1])
%!assert_equal (size (geornd (0.5*ones (2,2))), [2, 2])
%!assert_equal (size (geornd (0.5, 3)), [3, 3])
%!assert_equal (size (geornd (0.5, [4 1])), [4, 1])
%!assert_equal (size (geornd (0.5, 4, 1)), [4, 1])
%!assert_equal (size (geornd (0.5, [])), [0, 0])
%!assert_equal (size (geornd (0.5, [2, 0, 2, 1])), [2, 0, 2])
%!assert_equal (size (geornd (1, -1)), [0, 0])
%!assert_equal (size (geornd (1, [2, -1, 2])), [2, 0, 2])
%!assert_equal (size (geornd (1, 2, -1, 5)), [2, 0, 5])

## Test class of input preserved
%!assert_equal (class (geornd (0.5)), "double")
%!assert_equal (class (geornd (single (0.5))), "single")
%!assert_equal (class (geornd (single ([0.5 0.5]))), "single")
%!assert_equal (class (geornd (single (0))), "single")
%!assert_equal (class (geornd (single (1))), "single")

## Test input validation
%!error<geornd: function called with too few input arguments.> geornd ()
%!error<geornd: PS must not be complex.> geornd (i)
%!error<geornd: SZ must be a scalar or a row vector of integers.> ...
%! geornd (1, 1.2)
%!error<geornd: SZ must be a scalar or a row vector of integers.> ...
%! geornd (1, ones (2))
%!error<geornd: SZ must be a scalar or a row vector of integers.> ...
%! geornd (1, [2 0 2.5])
%!error<geornd: SZ must be a scalar or a row vector of integers.> ...
%! geornd (ones (2), ones (2))
%!error<geornd: dimensions must be integers.> ...
%! geornd (1, 2, 1.5, 5)
%!error<geornd: PS must be scalar or of size SZ.> geornd (ones (2,2), 3)
%!error<geornd: PS must be scalar or of size SZ.> geornd (ones (2,2), [3, 2])
%!error<geornd: PS must be scalar or of size SZ.> geornd (ones (2,2), 2, 3)
