why my plot is not correct?

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wenchong chen
wenchong chen 2021-4-11
评论： DGM 2021-4-11
here is my code
x = -5:0.1:5
y = x.^(1/3)
plot(x,y)
  2 个评论
wenchong chen
wenchong chen 2021-4-11
it is working, but it is giving me wrong number
wenchong chen
wenchong chen 2021-4-11
also there is a Warning: Imaginary parts of complex X and/or Y arguments ignored.

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回答（2 个）

Paul
Paul 2021-4-11
If you're looking for a plot with odd symmetry, try:
plot(x,nthroot(x,3)) % check doc nthroot for details
DGM
DGM 2021-4-11
I'm not sure what you intend the correct number to be. You're doing the cube root of negative numbers. They're going to be complex.
By default, plot() will only plot the real component of complex inputs. If you're expecting the plot to be symmetrical, consider plotting abs(y) to get the magnitude of the complex-valued region.
x = -5:0.1:5;
y = x.^(1/3);
h1=plot(x,real(y)); hold on
h2=plot(x,imag(y));
h3=plot(x,abs(y));
legend([h1,h2,h3],'real','imaginary','magnitude','location','southeast')
  2 个评论
wenchong chen
wenchong chen 2021-4-11
the^1/3 of negative numbers should be negative right? why both negative and positive side are both positive number?
DGM
DGM 2021-4-11
You probably want Paul's answer below. nthroot() calculates the real root, whereas power() or .^ calculates the complex root. The web docs include such an example.

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