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

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?

Answer 1

[Steven Lord]

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.

[Donald]

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!