Working With Inverse of Polynomials

Question

Daniel Scrobe about 9 hours 前

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编辑： Torsten about 3 hours 前

Hello, this is my first post in this form and I am new to MatLab. I would like to take the inverse of a polynomial in factored form and express the answer in polynomial form. For example, I wish to convert 10/((x+3)^2(x+5)) in regular polynomial form.

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Walter Roberson about 3 hours 前

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It is difficult to tell what you want?

syms x

f = 10/((x+3).^2.*(x+5))

f =

[N, D] = numden(f)

N =

10

D =

C = coeffs(D, x)

C =

poly2sym(C, x)

ans =

tf(double(N), double(C))

ans = 10 -------------------------- 45 s^3 + 39 s^2 + 11 s + 1 Continuous-time transfer function.

Torsten about 3 hours 前

编辑：Torsten about 3 hours 前

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syms x

p = (x+3)^2*(x+5)

p =

expand(p)

ans =

coeffs(p)

ans =

What do you want to do next ?

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Answer 1

Sam Chak about 8 hours 前

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Hi @Daniel Scrobe

Are looking for an inverse like this?

syms x

f(x) = 10/((x+3)^2*(x+5))

f(x) =

g = finverse(f)

g(x) =

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Answer 2

Naga about 8 hours 前

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编辑：Walter Roberson about 4 hours 前

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Hello Daniel,

To convert a polynomial in factored form to regular polynomial form, you can use the poly function in MATLAB. Here's an example:

% Define the factored polynomial
num = 10;
den = conv(conv([1 3], [1 3]), [1 5]);
% Convert to regular polynomial form
coeffs = num * poly(den)
coeffs = 1x5
          10        -960       27740     -219840      193050
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The 'poly' function converts the factored form to regular polynomial form, and then we multiply it by the numerator to get the coefficients of the regular polynomial. Please refer to the following documentation for more information on 'poly' function:

https://www.mathworks.com/help/matlab/ref/poly.html

Hope this helps!

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Daniel Scrobe about 5 hours 前

编辑：Daniel Scrobe about 5 hours 前

Hello Naga,

When I divide the numerator by the denominator, I get an error using the "/" symbol: Matrix dimensions must agree. How would I get rid of the denominator? I was thinking if I could take the inverse of it, I could bring that up into the numerator section.

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