Mercurial > hg > octave-lyh
annotate scripts/specfun/perms.m @ 9245:16f53d29049f
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| author | John W. Eaton <jwe@octave.org> |
|---|---|
| date | Fri, 22 May 2009 10:46:00 -0400 |
| parents | 1bf0ce0930be |
| children | 804c21f3659b |
| rev | line source |
|---|---|
| 9245 | 1 ## Copyright (C) 2001, 2006, 2007, 2009 Paul Kienzle |
| 5827 | 2 ## |
| 3 ## This file is part of Octave. | |
| 4 ## | |
| 5 ## Octave is free software; you can redistribute it and/or modify it | |
| 6 ## under the terms of the GNU General Public License as published by | |
| 7016 | 7 ## the Free Software Foundation; either version 3 of the License, or (at |
| 8 ## your option) any later version. | |
| 5827 | 9 ## |
| 10 ## Octave is distributed in the hope that it will be useful, but | |
| 11 ## WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
| 13 ## General Public License for more details. | |
| 14 ## | |
| 15 ## You should have received a copy of the GNU General Public License | |
| 7016 | 16 ## along with Octave; see the file COPYING. If not, see |
| 17 ## <http://www.gnu.org/licenses/>. | |
| 5827 | 18 |
| 19 ## -*- texinfo -*- | |
| 20 ## @deftypefn {Function File} {} perms (@var{v}) | |
| 21 ## | |
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22 ## Generate all permutations of @var{v}, one row per permutation. The |
| 5827 | 23 ## result has size @code{factorial (@var{n}) * @var{n}}, where @var{n} |
| 24 ## is the length of @var{v}. | |
| 25 ## | |
| 6754 | 26 ## As an example, @code{perms([1, 2, 3])} returns the matrix |
| 27 ## @example | |
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28 ## @group |
| 6754 | 29 ## 1 2 3 |
| 30 ## 2 1 3 | |
| 31 ## 1 3 2 | |
| 32 ## 2 3 1 | |
| 33 ## 3 1 2 | |
| 34 ## 3 2 1 | |
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Rik <rdrider0-list@yahoo.com>
parents:
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35 ## @end group |
| 6754 | 36 ## @end example |
| 5827 | 37 ## @end deftypefn |
| 38 | |
| 39 function A = perms (v) | |
| 6391 | 40 if (nargin != 1) |
| 41 print_usage (); | |
| 42 endif | |
| 5827 | 43 v = v(:); |
| 44 n = length (v); | |
| 45 if (n == 1) | |
| 46 A = v; | |
| 47 else | |
| 48 B = perms (v(1:n-1)); | |
| 49 Bidx = 1:size (B, 1); | |
| 50 A = v(n) * ones (prod (2:n), n); | |
| 51 A(Bidx,1:n-1) = B; | |
| 52 k = size (B, 1); | |
| 53 for i = n-1:-1:2 | |
| 54 A(k+Bidx,1:i-1) = B(Bidx,1:i-1); | |
| 55 A(k+Bidx,i+1:n) = B(Bidx,i:n-1); | |
| 56 k = k + size (B, 1); | |
| 57 endfor | |
| 58 A(k+Bidx,2:n) = B; | |
| 59 endif | |
| 60 endfunction |