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1 ## Copyright (C) 1996, 1997 John W. Eaton |
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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 3 of the License, or (at |
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8 ## your option) 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, see |
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17 ## <http://www.gnu.org/licenses/>. |
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18 |
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19 ## -*- texinfo -*- |
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20 ## @deftypefn {Function File} {} orth (@var{a}, @var{tol}) |
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21 ## Return an orthonormal basis of the range space of @var{a}. |
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22 ## |
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23 ## The dimension of the range space is taken as the number of singular |
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24 ## values of @var{a} greater than @var{tol}. If the argument @var{tol} is |
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25 ## missing, it is computed as |
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26 ## |
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27 ## @example |
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28 ## max (size (@var{a})) * max (svd (@var{a})) * eps |
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29 ## @end example |
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30 ## @end deftypefn |
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31 |
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32 ## Author: KH <Kurt.Hornik@wu-wien.ac.at> |
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33 ## Created: 24 December 1993. |
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34 ## Adapted-By: jwe |
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35 |
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36 function retval = orth (A, tol) |
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37 |
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38 if (nargin == 1 || nargin == 2) |
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39 |
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40 [U, S, V] = svd (A); |
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41 |
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42 [rows, cols] = size (A); |
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43 |
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44 [S_nr, S_nc] = size (S); |
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45 |
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46 if (S_nr == 1 || S_nc == 1) |
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47 s = S(1); |
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48 else |
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49 s = diag (S); |
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50 endif |
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51 |
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52 if (nargin == 1) |
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53 tol = max (size (A)) * s (1) * eps; |
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54 endif |
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55 |
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56 rank = sum (s > tol); |
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57 |
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58 if (rank > 0) |
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59 retval = -U (:, 1:rank); |
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60 else |
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61 retval = zeros (rows, 0); |
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62 endif |
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63 |
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64 else |
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65 |
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66 print_usage (); |
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67 |
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68 endif |
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69 |
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70 endfunction |
