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annotate scripts/polynomial/poly.m @ 1336:33d5c2471c09

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[project @ 1995-08-25 01:53:42 by jwe]
author jwe
date Fri, 25 Aug 1995 01:53:42 +0000
parents 611d403c7f3d
children 5d29638dd524
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1 # Copyright (C) 1995 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 the
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7 # Free Software Foundation; either version 2, or (at your option) any
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8 # later version.
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9 #
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10 # Octave is distributed in the hope that it will be useful, but WITHOUT
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11 # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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12 # FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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13 # 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 02111-1307, USA.
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18
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19 function y = poly (x)
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20
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21 # usage: poly (x)
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22 #
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23 # If A is a square n-by-n matrix, poly (A) is the row vector of
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24 # the coefficients of det (z * eye(n) - A), the characteristic
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25 # polynomial of A.
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26 #
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27 # If x is a vector, poly (x) is a vector of coefficients of the
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28 # polynomial whose roots are the elements of x.
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29
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30 # Written by KH (Kurt.Hornik@neuro.tuwien.ac.at) Dec 24, 1993.
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31
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32 if (nargin != 1)
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33 usage ("poly (x)");
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34 endif
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35
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36 m = min (size (x));
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37 n = max (size (x));
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38 if (m == 0)
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39 y = 1;
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40 elseif (m == 1)
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41 v = x;
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42 elseif (m == n)
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43 v = eig (x);
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44 else
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45 usage ("poly (x), where x is a vector or a square matrix");
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46 endif
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47
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48 y = zeros (1, n+1);
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49 y(1) = 1;
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50 for j = 1:n;
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51 y(2:(j+1)) = y(2:(j+1)) - v(j) .* y(1:j);
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52 endfor
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53
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54 if (all (all (imag (x) == 0)))
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55 y = real (y);
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56 endif
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57
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58 endfunction