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annotate scripts/linear-algebra/cond.m @ 7016:93c65f2a5668

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[project @ 2007-10-12 06:40:56 by jwe]
author jwe
date Fri, 12 Oct 2007 06:41:26 +0000
parents 34f96dd5441b
children a1dbe9d80eee
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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} {} cond (@var{a})
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21 ## Compute the (two-norm) condition number of a matrix. @code{cond (a)} is
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22 ## defined as @code{norm (a) * norm (inv (a))}, and is computed via a
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23 ## singular value decomposition.
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24 ## @seealso{norm, svd, rank}
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25 ## @end deftypefn
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27 ## Author: jwe
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29 function retval = cond (a)
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31 if (nargin == 1)
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32 if (ndims (a) > 2)
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33 error ("cond: Only valid on 2-D objects")
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34 endif
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36 [nr, nc] = size (a);
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37 if (nr == 0 || nc == 0)
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38 retval = 0.0;
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39 endif
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40 if (any (any (isinf (a) | isnan (a))))
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41 error ("cond: argument must not contain Inf or NaN values");
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42 else
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43 sigma = svd (a);
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44 sigma_1 = sigma(1);
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45 sigma_n = sigma(length (sigma));
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46 if (sigma_1 == 0 || sigma_n == 0)
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47 retval = Inf;
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48 else
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49 retval = sigma_1 / sigma_n;
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50 endif
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51 endif
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52 else
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53 print_usage ();
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54 endif
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55
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56 endfunction