What does roots/ eig do exactly?

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I want to write a programm on Matlab, without using implemented functions. This programm should be similiar to the Matlab function roots. But I am not sure what roots does, is there any possibility to read something like a pseudo-code of roots or eig? Or is it possible to find .m file that fullfills this conditions?
Is roots simply using the QR decomposition with shifts ?

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Sean de Wolski
Sean de Wolski on 5 Aug 2015
Edited: Sean de Wolski on 5 Aug 2015
>>edit roots
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Thomas Waljor
Thomas Waljor on 5 Aug 2015
For my bachelor thesis I wrote a programm that computes the roots of a polynomial quiet fast. One part of mine assignment is to compare this algorithm with the in Matlab implemented roots function. It is impossible to compare them directly, since I had to use Matlab to programm the first algorithm. Right now I try to figure out how roots computes the roots of a polynomial.
James Tursa
James Tursa on 5 Aug 2015
By looking at the code for roots you have that answer. It constructs a matrix where the characteristic polynomial of that matrix is your polynomial. Then it uses eig to find eigenvalues of that matrix, which will be equal to the roots of the characteristic polynomial.

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