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1 ## Copyright (C) 2001 Paul Kienzle |
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2 ## |
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3 ## This file is part of Octave. |
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4 ## |
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5 ## Octave is free software; you can redistribute it and/or modify it |
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6 ## under the terms of the GNU General Public License as published by |
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7 ## the Free Software Foundation; either version 2, or (at your option) |
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8 ## any later version. |
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9 ## |
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10 ## Octave is distributed in the hope that it will be useful, but |
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of |
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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13 ## General Public License for more details. |
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14 ## |
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15 ## You should have received a copy of the GNU General Public License |
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16 ## along with Octave; see the file COPYING. If not, write to the Free |
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17 ## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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18 ## 02110-1301, USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {} perms (@var{v}) |
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22 ## |
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23 ## Generate all permutations of @var{v}, one row per permutation. The |
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24 ## result has size @code{factorial (@var{n}) * @var{n}}, where @var{n} |
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25 ## is the length of @var{v}. |
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26 ## |
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27 ## As an example, @code{perms([1, 2, 3])} returns the matrix |
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28 ## @example |
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29 ## 1 2 3 |
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30 ## 2 1 3 |
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31 ## 1 3 2 |
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32 ## 2 3 1 |
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33 ## 3 1 2 |
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34 ## 3 2 1 |
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35 ## @end example |
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36 ## @end deftypefn |
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37 |
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38 function A = perms (v) |
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39 if (nargin != 1) |
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40 print_usage (); |
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41 endif |
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42 v = v(:); |
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43 n = length (v); |
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44 if (n == 1) |
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45 A = v; |
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46 else |
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47 B = perms (v(1:n-1)); |
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48 Bidx = 1:size (B, 1); |
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49 A = v(n) * ones (prod (2:n), n); |
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50 A(Bidx,1:n-1) = B; |
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51 k = size (B, 1); |
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52 for i = n-1:-1:2 |
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53 A(k+Bidx,1:i-1) = B(Bidx,1:i-1); |
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54 A(k+Bidx,i+1:n) = B(Bidx,i:n-1); |
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55 k = k + size (B, 1); |
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56 endfor |
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57 A(k+Bidx,2:n) = B; |
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58 endif |
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59 endfunction |
