roots_

Version 1.1.2 (1.44 KB) by Kenneth Johnson
roots_(c) works with poorly scaled polynomials and does not return zero when c(end) is nonzero.
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Updated 25 Aug 2024

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This fixes the MATLAB roots function to work with poorly scaled polynomials. For example,
c = 10.^(20:-1:0);
x = roots(c); max(abs(polyval(c,x))) % 7.647251195518823e-08
x = roots_(c); max(abs(polyval(c,x))) % 7.257804400984254e-14
This also fixes the MATLAB roots function to work with small roots. For example, roots([1,1,1,1e-32]) incorrectly gives a root of exact zero. roots_([1,1,1,1e-32]) gives the correct root of -1e-32.
(Reported as Case Number 04335183 on 30 Jun 2020 and Case Number 07198299 on 05 Aug 2024.)

Cite As

Kenneth Johnson (2024). roots_ (https://www.mathworks.com/matlabcentral/fileexchange/84280-roots_), MATLAB Central File Exchange. Retrieved .

MATLAB Release Compatibility
Created with R2024a
Compatible with any release
Platform Compatibility
Windows macOS Linux

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Version Published Release Notes
1.1.2

Fix problem with complex coefficients. (Replace find(logical(c)) with find(c~=0).)
1.1.1

Eliminate infinite roots.
1.1.0

Modified to work with poorly scaled polynomials.
1.0.1

Added tag "polynomial roots".
1.0.0