How can I plot all iterations of my for loop?

Question

Lina Alami 2020-11-16

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https://ww2.mathworks.cn/matlabcentral/answers/650148-how-can-i-plot-all-iterations-of-my-for-loop

评论： Lina Alami 2020-11-17

Hey I'm kind of new to MALAB, so bear with me please!

I'm trying to plot the real and imaginary parts of the eigenvalue results in my for loop, as a function of I from [0,4].

Here's my code:

figure
hold on
for I = 0:0.1:4
    p = [-1/3 0 -1 (I-2)]
    r = roots(p)
    x = r(3)
    A = [(1 - x^2) -40 ; 1/800 -1/40]
    e = eig(A)
    plot(I,real(e(1)),'r-',I,imag(e(1)),'b-')
end

My plot keeps coming up empty, and no error shows up. what can i do?

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Answer 1

gonzalo Mier 2020-11-17

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在 MATLAB Online 中打开

Right now, each plot is plotting only one point. To achieve the behavior you want, create the vectors and plot them outside the for loop

figure
hold on
e=[];
for I = 0:0.1:4
    p = [-1/3 0 -1 (I-2)]
    r = roots(p)
    x = r(3)
    A = [(1 - x^2) -40 ; 1/800 -1/40]
    e = [e,eig(A)]
end
 plot(0:0.1:4,real(e(1,:)),'r-',0:0.1:4,imag(e(2,:)),'b-')