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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, 675 Mass Ave, Cambridge, MA 02139, 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 = [1, zeros (1, n)]; |
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49 for j = 1:n; |
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50 y(2:(j+1)) = y(2:(j+1)) - v(j) .* y(1:j); |
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51 endfor |
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52 |
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53 if (all (all (imag (x) == 0))) |
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54 y = real (y); |
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55 endif |
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56 |
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57 endfunction |
