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