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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 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} {} cond (@var{a}) |
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22 ## Compute the (two-norm) condition number of a matrix. @code{cond (a)} is |
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23 ## defined as @code{norm (a) * norm (inv (a))}, and is computed via a |
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24 ## singular value decomposition. |
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25 ## @end deftypefn |
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26 ## |
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27 ## @seealso{norm, svd, and rank} |
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28 |
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29 ## Author: jwe |
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30 |
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31 function retval = cond (a) |
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32 |
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33 if (nargin == 1) |
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34 if (ndims (a) > 2) |
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35 error ("cond: Only valid on 2-D objects") |
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36 endif |
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37 |
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38 [nr, nc] = size (a); |
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39 if (nr == 0 || nc == 0) |
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40 retval = 0.0; |
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41 endif |
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42 if (any (any (isinf (a) | isnan (a)))) |
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43 error ("cond: argument must not contain Inf or NaN values"); |
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44 else |
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45 sigma = svd (a); |
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46 sigma_1 = sigma(1); |
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47 sigma_n = sigma(length (sigma)); |
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48 if (sigma_1 == 0 || sigma_n == 0) |
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49 retval = Inf; |
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50 else |
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51 retval = sigma_1 / sigma_n; |
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52 endif |
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53 endif |
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54 else |
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55 usage ("cond (a)"); |
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56 endif |
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57 |
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58 endfunction |
