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[project @ 2005-02-23 00:40:57 by jwe]
author jwe
date Wed, 23 Feb 2005 00:40:57 +0000
parents 3e3e14ad5149
children 4c8a2e4e0717
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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, 59 Temple Place - Suite 330, Boston, MA
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18 ## 02111-1307, USA.
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19
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20 ## -*- texinfo -*-
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21 ## @deftypefn {Function File} {} poly (@var{a})
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22 ## If @var{a} is a square @math{N}-by-@math{N} matrix, @code{poly (@var{a})}
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23 ## is the row vector of the coefficients of @code{det (z * eye (N) - a)},
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24 ## the characteristic polynomial of @var{a}. If @var{x} is a vector,
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25 ## @code{poly (@var{x})} is a vector of coefficients of the polynomial
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26 ## whose roots are the elements of @var{x}.
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27 ## @end deftypefn
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29 ## Author: KH <Kurt.Hornik@neuro.tuwien.ac.at>
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30 ## Created: 24 December 1993
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31 ## Adapted-By: jwe
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33 function y = poly (x)
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35 if (nargin != 1)
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36 usage ("poly (x)");
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37 endif
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38
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39 m = min (size (x));
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40 n = max (size (x));
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41 if (m == 0)
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42 y = 1;
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43 return;
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44 elseif (m == 1)
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45 v = x;
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46 elseif (m == n)
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47 v = eig (x);
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48 else
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49 usage ("poly (x), where x is a vector or a square matrix");
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50 endif
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51
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52 y = zeros (1, n+1);
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53 y(1) = 1;
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54 for j = 1:n;
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55 y(2:(j+1)) = y(2:(j+1)) - v(j) .* y(1:j);
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56 endfor
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57
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58 if (all (all (imag (x) == 0)))
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59 y = real (y);
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60 endif
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61
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62 endfunction