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diff --git a/octave_packages/m/statistics/distributions/gamcdf.m b/octave_packages/m/statistics/distributions/gamcdf.m
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+## Copyright (C) 2012 Rik Wehbring
+## Copyright (C) 1995-2012 Kurt Hornik
+##
+## 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/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {} gamcdf (@var{x}, @var{a}, @var{b})
+## For each element of @var{x}, compute the cumulative distribution
+## function (CDF) at @var{x} of the Gamma distribution with shape
+## parameter @var{a} and scale @var{b}.
+## @end deftypefn
+
+## Author: TT <Teresa.Twaroch@ci.tuwien.ac.at>
+## Description: CDF of the Gamma distribution
+
+function cdf = gamcdf (x, a, b)
+
+  if (nargin != 3)
+    print_usage ();
+  endif
+
+  if (!isscalar (a) || !isscalar (b))
+    [retval, x, a, b] = common_size (x, a, b);
+    if (retval > 0)
+      error ("gamcdf: X, A, and B must be of common size or scalars");
+    endif
+  endif
+
+  if (iscomplex (x) || iscomplex (a) || iscomplex (b))
+    error ("gamcdf: X, A, and B must not be complex");
+  endif
+
+  if (isa (x, "single") || isa (a, "single") || isa (b, "single"))
+    cdf = zeros (size (x), "single");
+  else
+    cdf = zeros (size (x));
+  endif
+
+  k = isnan (x) | !(a > 0) | !(a < Inf) | !(b > 0) | !(b < Inf);
+  cdf(k) = NaN;
+
+  k = (x > 0) & (a > 0) & (a < Inf) & (b > 0) & (b < Inf);
+  if (isscalar (a) && isscalar (b))
+    cdf(k) = gammainc (x(k) / b, a);
+  else
+    cdf(k) = gammainc (x(k) ./ b(k), a(k));
+  endif
+
+endfunction
+
+
+%!shared x,y
+%! x = [-1 0 0.5 1 2 Inf];
+%! y = [0, gammainc(x(2:end), 1)];
+%!assert(gamcdf (x, ones(1,6), ones(1,6)), y);
+%!assert(gamcdf (x, 1, ones(1,6)), y);
+%!assert(gamcdf (x, ones(1,6), 1), y);
+%!assert(gamcdf (x, [0 -Inf NaN Inf 1 1], 1), [NaN NaN NaN NaN y(5:6)]);
+%!assert(gamcdf (x, 1, [0 -Inf NaN Inf 1 1]), [NaN NaN NaN NaN y(5:6)]);
+%!assert(gamcdf ([x(1:2) NaN x(4:6)], 1, 1), [y(1:2) NaN y(4:6)]);
+
+%% Test class of input preserved
+%!assert(gamcdf ([x, NaN], 1, 1), [y, NaN]);
+%!assert(gamcdf (single([x, NaN]), 1, 1), single([y, NaN]), eps("single"));
+
+%% Test input validation
+%!error gamcdf ()
+%!error gamcdf (1)
+%!error gamcdf (1,2)
+%!error gamcdf (1,2,3,4)
+%!error gamcdf (ones(3),ones(2),ones(2))
+%!error gamcdf (ones(2),ones(3),ones(2))
+%!error gamcdf (ones(2),ones(2),ones(3))
+%!error gamcdf (i, 2, 2)
+%!error gamcdf (2, i, 2)
+%!error gamcdf (2, 2, i)
+