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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 ## usage: polyval (c, x) |
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21 ## |
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22 ## Evaluate a polynomial. |
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23 ## |
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24 ## In octave, a polynomial is represented by it's coefficients (arranged |
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25 ## in descending order). For example a vector c of length n+1 corresponds |
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26 ## to the following nth order polynomial |
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27 ## |
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28 ## p(x) = c(1) x^n + ... + c(n) x + c(n+1). |
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29 ## |
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30 ## polyval(c,x) will evaluate the polynomial at the specified value of x. |
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31 ## |
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32 ## If x is a vector or matrix, the polynomial is evaluated at each of the |
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33 ## elements of x. |
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34 ## |
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35 ## SEE ALSO: polyvalm, poly, roots, conv, deconv, residue, filter, |
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36 ## polyderiv, polyinteg |
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37 |
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38 ## Author: Tony Richardson <amr@mpl.ucsd.edu> |
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39 ## Created: June 1994 |
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40 ## Adapted-By: jwe |
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41 |
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42 function y = polyval (c, x) |
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43 |
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44 if (nargin != 2) |
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45 usage ("polyval (c, x)"); |
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46 endif |
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47 |
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48 if (! (is_vector (c) || isempty (c))) |
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49 error ("polyval: first argument must be a vector."); |
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50 endif |
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51 |
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52 if (isempty (x)) |
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53 y = []; |
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54 return; |
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55 endif |
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56 |
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57 if (length (c) == 0) |
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58 y = c; |
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59 return; |
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60 endif |
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61 |
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62 n = length (c); |
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63 y = c (1) * ones (rows (x), columns (x)); |
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64 for index = 2:n |
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65 y = c (index) + x .* y; |
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66 endfor |
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67 |
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68 endfunction |
