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# How to use the result of my matrix calculation to create 2D plot

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Jun Xiao on 31 Oct 2019
Commented: Daniel M on 1 Nov 2019
I tried to plot my the result of my matrix calculation. However, my matlab said that my calculation result lambda1 or Z is not a matrix so I cannot plot without using the command plot3. But I have to plot the 2D figure with different colors represent different result of lambda1. And the commands like pcolor and color require my results to be matrix. What should I do?
n1 = 1.5;
n2 = 3.0;
b1 = 8*10.^(-18);
c1 = pi*10.^(-13);
k1 = (2*pi)*n1;
k2 = (2*pi)*n2;
d1 = [1 1; k1 -k1];
d2 = [1 1; k2 -k2];
t1 = inv(d1);
t2 = inv(d2);
for l1= 1:0.1:10
for l2= 1:0.1:10
p2= [exp(i*k2*l2) 0; 0 exp(-i*k2*l2)];
p1= [exp(i*k1*l1) 0; 0 exp(-i*k1*l1)];
M = t1*d2*p2*t2*d1*p1;
M1= real(M);
[X,Y]= eig(M1);
lambda1 = [0 1]*Y*[0;1];
lambda2 = real([1 0]*Y*[1;0]);
Z = lambda1;
hold on
end
end
pcolor(l1,l2,Z)
##### 1 CommentShowHide None
KALYAN ACHARJYA on 31 Oct 2019
Formulate the question in an easy way so that it can be understood easily.

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### Accepted Answer

Daniel M on 31 Oct 2019
l1,l2, and Z are all a single value. You need to understand how to store values in a for loop:
##### 2 CommentsShowHide 1 older comment
Daniel M on 1 Nov 2019
Those variables don't really exist outside of the for loop. They look like vectors, but they're not. Their value is only the value of that iteration, and therefore outside of the loop they only keep the value of the last iteration. Just recreate them after the loop.

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