I am trying to compute the zero of a function using fzero, but the system always says my function must be finite and real. How can I solve that? Thank you!

1 view (last 30 days)
I want to find the zero of f(x) = 2(3x+4)(x^3+4x^2-10)/(x^2(3x+8)^2)
Here is the screenshot for the error:

Accepted Answer

Matt J
Matt J on 24 Sep 2021
Edited: Matt J on 24 Sep 2021
Clearly, your function is non-finite at x=0. There is a factor of x^2 in its denominator.
Regardless, fzero() is the wrong tool for analyzing a rational function. Just use roots() to get the roots of the numerator polynomial.
r=[roots([1 0 4 -10]).' ,-4/3];
r=real( r( abs(imag(r))<1e-10 ))
r = 1×2
1.5568 -1.3333
And, of course, you must make sure that none of the numerator roots coincide with any denominator roots, but that is obvious here by inspection.

More Answers (0)

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!