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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} {} 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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28 |
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29 ## Author: KH <Kurt.Hornik@wu-wien.ac.at> |
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30 ## Created: 24 December 1993 |
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31 ## Adapted-By: jwe |
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32 |
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33 function y = poly (x) |
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34 |
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35 if (nargin != 1) |
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36 print_usage (); |
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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 print_usage (); |
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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 |
