Plotting complex roots of polynomial

26 次查看（过去 30 天）
Thomas Sun
Thomas Sun 2020-5-19
评论： David Goodmanson 2020-5-19
Hi I need to plot of the roots of a polynomial in the complex plane. This is the code I have so far but it doesn't seem to be working.
z = -1:0.01:1;
p = z.^9 + z.^8 - z.^7 + z.^6 - z.^5 + z + 1;
plot(z,p)
hold on
r = roots(p);
scatter(real(r),imag(r))
hold off

请先登录，再回答此问题。

回答（1 个）

David Goodmanson
David Goodmanson 2020-5-19
Hi Thomas,
what the roots function is looking for is the coefficients of the powers of z in decreasing order. In this case that would be
r = roots([1 1 -1 1 -1 0 0 0 1 1])
This shows one real root at approximately -1.9, and eight complex roots. If you use
z = -2:0.01:1;
you can see the curve go through the real root.
  4 个评论
显示 2更早的评论
Thomas Sun
Thomas Sun 2020-5-19
Hi Dave
I tried your code but with it a graph for p doesnt even show up
David Goodmanson
David Goodmanson 2020-5-19
what do you get for the sizes of z and p?
maybe if you tried 'close all' and put 'figure(1)' just before the plot command ....?

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Polynomials 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