Plotting a polynomial function with roots

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Christina Cruz
Christina Cruz il 23 Ott 2016
Commentato: Robert il 23 Ott 2016
Hi there! I have barely have an idea of what to do with MatLab as of now and my professor pretty much leaves us to do the problems on our own without even teaching the basics first.
He gave us this problem: plot the function showing its roots. Label the roots r1, r2, etc.
f(x) = (x^3) - 10/((2-x)^2) + 25
i got one root through the fixed point iteration method which is roughly 1.3997 but i don't know how to plot this. Any help would be highly appreciated. Thanks in advance!
  1 Commento
Robert
Robert il 23 Ott 2016
Modificato: Robert il 23 Ott 2016
Please don't forget to accept the answer Thanks!
syms x
f = (x^3) - 10/((2-x)^2) + 25 % Original function
%same function but rearranged
%Matlab needs to rearrange the function to be in the form of a polynomial
f_rearranged = x^5 -4*x^4 + 4*x^3 +25*x^2 -100*x+90
% Collect the coefficients in decending order
[My_coeffs,~] = coeffs(f_rearranged,x)
roots(My_coeffs) %Get the roots

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Risposte (1)

Andrei Bobrov
Andrei Bobrov il 23 Ott 2016
syms x
f = x^3 - 10/(2-x)^2 + 25
[n,~] = numden(f);
[c,~] = coeffs(n);
your_roots = roots(double(c));
your_roots = your_roots(imag(your_roots)==0)
  1 Commento
Robert
Robert il 23 Ott 2016
Why are you removing imaginary roots? The answer is incomplete

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