Why do two functions in my plot "switch" positions when plotted?

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Donald
Donald 2015-9-25
编辑： Walter Roberson 2015-9-25
Here is my code:
clear
clc
m1 = 1;
m2 = 2;
m3 = 1;
k1 = 2000:8000;
k2 = 2000;
k3 = 6000;
M = [ m1 0 0; 0 m2 0; 0 0 m3]
for n = 1:length(k1);
K = [k1(n)+k2 -k2 0; -k2 k2+k3+3 -k3; 0 -k3 k3];
EV = eig(-inv(M)*K);
w1(n) = sqrt(abs(EV(1)));
w2(n) = sqrt(abs(EV(2)));
w3(n) = sqrt(abs(EV(3)));
end
figure(1)
plot(k1,w1/(2*pi),k1,w2/(2*pi),k1,w3/(2*pi))
legend w1 w2 w3
title('Varying k1')
ylabel('Frequency (Hz)')
xlabel('k1')
my plot looks like the picture attached. I cannot figure out why w2 and w3 seem to jump to one another after about 7000.
How can I resolve this?

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采纳的回答

Steven Lord
Steven Lord 2015-9-25
EIG doesn't guarantee it always returns the eigenvalues in any particular order. If you want them to always be returned in increasing order or always in decreasing order, SORT them.
  1 个评论
Donald
Donald 2015-9-25
I'm not too familiar with using the EIG function, after going back and using the sort function to obtain the correct corresponding eigenvalues, the plot was fixed.
Thank you!

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