Increase the precision of the finding roots
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Atta Oveisi
on 17 Nov 2011
Commented: Walter Roberson
on 21 Nov 2018
Hi I have written a m file in which I'm trying to find ROOTs of a polynomial of of 6'th degree.I do this in a cycle using "do" because a parameter in the coefficients of the polynomial have to change in each step and the ROOTs should be calculated and saved for further mathmatical calculations. The problem is that in this exact case of mine the real part of each root is very small so that matlab ignores them in some steps and doesnt ignore in other cases(by cases I mean change of that parameter).and this cause the results to oscillate.I know that this real part despite it's smallness is'nt zero. HOW CAN I INCREASE THE PRECISION IN THIS EXACT CASE? thanks for your attention.
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Accepted Answer
Walter Roberson
on 17 Nov 2011
If the function uses its own precision, then we would need to see the function in order to see how to increase the precision. There is not just one method for doing extended precision calculations.
If you have access to the symbolic toolbox, consider using that for the calculations.
Note: in any finite precision calculation scheme, there are calculations that will oscillate in the manner you describe.
4 Comments
Dima
on 21 Nov 2018
Try
roots(conv(conv([1 -2 1],[1 -2 1]),[1 -2 1]))
There is still a problem with multiple roots.
Walter Roberson
on 21 Nov 2018
You are correct that roots does not do a good job on that . solve(poly2sym()) of the vector produces exact solutions though .
More Answers (1)
Andrew Newell
on 17 Nov 2011
3 Comments
Andrew Newell
on 17 Nov 2011
I'm just saying that if you don't have any compelling reason to write the m file yourself, you'd be better off using the MATLAB function.
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