Increase the precision of the finding roots

4 次查看（过去 30 天）
Atta Oveisi
Atta Oveisi 2011-11-17
评论： Walter Roberson 2018-11-21
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.

请先登录，再回答此问题。

采纳的回答

Walter Roberson
Walter Roberson 2011-11-17
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 个评论
显示 2更早的评论
Dima
Dima 2018-11-21
Try
roots(conv(conv([1 -2 1],[1 -2 1]),[1 -2 1]))
There is still a problem with multiple roots.
Walter Roberson
Walter Roberson 2018-11-21
You are correct that roots does not do a good job on that . solve(poly2sym()) of the vector produces exact solutions though .

请先登录，再进行评论。

更多回答（1 个）

Andrew Newell
Andrew Newell 2011-11-17
Unless this is an exercise, you could just use roots to solve your problem.
  3 个评论
显示 1更早的评论
Andrew Newell
Andrew Newell 2011-11-17
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.
Atta Oveisi
Atta Oveisi 2011-11-17
I myself want to use "root" but the roblem is this function use it's own number of precision.my question is how to increase this.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Number Theory 的更多信息

标签

Community Treasure Hunt

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

Start Hunting!

Translated by