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[project @ 1994-10-11 00:34:13 by jwe] Initial revision
author jwe
date Tue, 11 Oct 1994 00:34:39 +0000
parents
children 3470f1e25a79
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787
c5d35bb139b6 [project @ 1994-10-11 00:34:13 by jwe]
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1 function y = poly (x)
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2 #
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3 # If A is a square n-by-n matrix, poly (A) is the row vector of
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4 # the coefficients of det (z * eye(n) - A), the characteristic
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5 # polynomial of A.
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6 # If x is a vector, poly (x) is a vector of coefficients of the
c5d35bb139b6 [project @ 1994-10-11 00:34:13 by jwe]
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7 # polynomial whose roots are the elements of x.
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8
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9 # Written by KH (Kurt.Hornik@neuro.tuwien.ac.at) on Dec 24, 1993
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10 # Copyright Dept of Probability Theory and Statistics TU Wien
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11
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12 m = min (size (x));
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13 n = max (size (x));
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14 if (m == 0)
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15 y = 1;
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16 elseif (m == 1)
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17 v = x;
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18 elseif (m == n)
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19 v = eig (x);
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20 else
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21 error ("usage: poly(x), where x is a vector or a square matrix");
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22 endif
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23
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24 y = [1, zeros (1, n)];
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25 for j = 1:n;
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26 y(2:(j+1)) = y(2:(j+1)) - v(j) .* y(1:j);
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27 endfor
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28
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29 if (all (all (imag (x) == 0)))
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30 y = real (y);
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31 endif
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32
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33 endfunction