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+## Copyright (C) 2004-2011 Paul Kienzle
+##
+## This file is part of Octave.
+##
+## Octave 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.
+##
+## Octave 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 Octave; see the file COPYING.  If not, see
+## <http://www.gnu.org/licenses/>.
+##
+## Original version by Paul Kienzle distributed as free software in the
+## public domain.
+
+## Undocumented internal function.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {} __isequal__ (@var{nans_compare_equal}, @var{x1}, @var{x2}, @dots{})
+## Undocumented internal function.
+## @end deftypefn
+
+## Actual implementation of sprand and sprandn happens here.
+
+function S = __sprand_impl__ (varargin)
+
+  if (nargin == 2)
+    m = varargin{1};
+    randfun = varargin{2};
+    [i, j] = find (m);
+    [nr, nc] = size (m);
+    S = sparse (i, j, randfun (size (i)), nr, nc);
+    return;
+  endif
+
+  [m, n, d, funname, randfun] = deal(varargin{:});
+
+  if (!(isscalar (m) && m == fix (m) && m > 0))
+    error ("%s: M must be an integer greater than 0", funname);
+  endif
+
+  if (!(isscalar (n) && n == fix (n) && n > 0))
+    error ("%s: N must be an integer greater than 0", funname);
+  endif
+
+  if (d < 0 || d > 1)
+    error ("%s: density D must be between 0 and 1", funname);
+  endif
+
+  mn = m*n;
+  k = round (d*mn);
+  idx = randperm (mn, k);
+
+  [i, j] = ind2sub ([m, n], idx);
+  S = sparse (i, j, randfun (k, 1), m, n);
+
+endfunction
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