Plotting complex roots of polynomial
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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
回答（1 个）
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
Thomas Sun
2020-5-19
David Goodmanson
2020-5-19
here is the code I used
z = -2:0.01:1;
p = z.^9 + z.^8 - z.^7 + z.^6 - z.^5 + z + 1;
r = roots([1 1 -1 1 -1 0 0 0 1 1])
plot(z,p);
hold on
plot(r,'o')
% scatter(real(r),imag(r)) % this one works too
hold off
Thomas Sun
2020-5-19
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 ....?
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2020-5-19
2020-5-19
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