Mercurial > octave
view scripts/specfun/factorial.m @ 23220:092078913d54
maint: Merge stable to default.
author | John W. Eaton <jwe@octave.org> |
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date | Wed, 22 Feb 2017 12:58:07 -0500 |
parents | ef4d915df748 3ac9f9ecfae5 |
children | 194eb4bd202b |
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## Copyright (C) 2000-2017 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/>. ## -*- texinfo -*- ## @deftypefn {} {} factorial (@var{n}) ## Return the factorial of @var{n} where @var{n} is a real non-negative ## integer. ## ## If @var{n} is a scalar, this is equivalent to @code{prod (1:@var{n})}. For ## vector or matrix arguments, return the factorial of each element in the ## array. ## ## For non-integers see the generalized factorial function @code{gamma}. ## Note that the factorial function grows large quite quickly, and even ## with double precision values overflow will occur if @var{n} > 171. For ## such cases consider @code{gammaln}. ## @seealso{prod, gamma, gammaln} ## @end deftypefn function x = factorial (n) if (nargin != 1) print_usage (); elseif (! isreal (n) || any (n(:) < 0 | n(:) != fix (n(:)))) error ("factorial: all N must be real non-negative integers"); endif x = round (gamma (n+1)); ## FIXME: Matlab returns an output of the same type as the input. ## This doesn't seem particularly worth copying--for example uint8 would ## saturate for n > 5. If desired, however, the following code could be ## uncommented. # if (! isfloat (x)) # x = cast (x, class (n)); # endif endfunction %!assert (factorial (5), prod (1:5)) %!assert (factorial ([1,2;3,4]), [1,2;6,24]) %!assert (factorial (70), exp (sum (log (1:70))), -128*eps) %!assert (factorial (0), 1) %!error factorial () %!error factorial (1,2) %!error <must be real non-negative integers> factorial (2i) %!error <must be real non-negative integers> factorial (-3) %!error <must be real non-negative integers> factorial (5.5)