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

How to plot the eigenvector calculated from eigs from the matrices created by freefem++?

Answer 1

[William Rose]

@AMIT,

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.