# how to plot eigenvector calculated from eigs from the matrices created by freefem++

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AMIT on 12 Feb 2024
Answered: William Rose on 12 Feb 2024
How to plot the eigenvector calculated from eigs from the matrices created by freefem++?

William Rose on 12 Feb 2024
quiver() is good for 2-D vectors; quiver3() for 3D.
For an example, I will use the magic square matrix, but I could use some opther random 2x2 matrix.
[v,d]=eigs(magic(2))
v = 2×2
-0.6000 -0.7071 -0.8000 0.7071
d = 2×2
5 0 0 -2
Plot the eigenvectors, with their bases at the origin:
quiver([0,0],[0,0],v(1,:),v(2,:));
axis equal; grid on
I use 'axis equal' to get a plot with equal scale factors on the x and y axes. If you don't do this, then vectors that are at right angles may look like they're not, etc.

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