Getting the Polynomial coefficients

Question

Kamuran 2015-4-26

0
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https://ww2.mathworks.cn/matlabcentral/answers/213624-getting-the-polynomial-coefficients

编辑： Kamuran 2015-4-26

Hello,

I am trying to identify if a given function is polynomial or not and if it is polynomial what the coefficients are. For example;

sym F x
F= 5*x^5+cos(x)*x^2+1   % This is not polynomial because of cos(x) and I want to identify that. 
[c,t] = coeffs(F);
PolyCoef = sym2poly(F);
c =
[ 5, 1, 1]  % no cos(x) is given in here
>> t
t =
[ [x^5, 1], [x^2, x], [1, 1]]  % no cos (x) is given in here

and sym2poly will give error. I am okay with the error as long as it does not stop the program and tell me that input function is not polynomial.

Thanks for the help.

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Answer 1

Mohammad Abouali 2015-4-26

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/213624-getting-the-polynomial-coefficients#answer_176717

在 MATLAB Online 中打开

Part I

You are using SYM() while using SYMS style of command. They are different. So change sym F x to syms F X or if you insist on using sym() then you need to use it properly such as F=sym('F')'

Part II

You can use that error to determine both the coefficient and if it was polynomial or not. You can use try/catch as follows:

try 
  PolyCoef = sym2poly(F);
catch
  disp('that was not a polynomial')
  PolyCoef=[];
end

In this case the program is not halted. If the statement(s) between catch and end (catch block) is only executed if, the statements between try and catch (try block), i.e. PolyCoef = sym2poly(F) in this case, produces any error. Refer to try/catch for further info on that.