Finding the eigenvectors of a 2nd multiplicity engenvalue

In summary, the conversation discusses finding the eigenvectors of a given matrix, with the eigenvalues being 1,3,3 and the corresponding eigenvectors being 1,-1,0 and 1,1,1. It is mentioned that for the other eigenvector with eigenvalue 3, there are multiple possible options that satisfy certain equations. Ultimately, it is concluded that there is no one definitive eigenbasis for this matrix.
  • #1
xdrgnh
417
0

Homework Statement


I'm given this matrice 2 1 0
1 2 0
0 0 3
and I need to find it's eigenvectors



Homework Equations





The Attempt at a Solution



So I get the eigenvalues to be 1,3,3 with 3 being the one with multiplicity of 2. For the eigenvector for 1 I get 1,-1,0 and for 3 I get 1,1,1 but here is the problem. For the other eigen vector for 3 the answer can be anything that satisfies x1=x2
x2=x1
x3=x3

so can something like 1,1,2 be the answer?
 
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  • #2
xdrgnh said:

Homework Statement


I'm given this matrice 2 1 0
1 2 0
0 0 3
and I need to find it's eigenvectors



Homework Equations





The Attempt at a Solution



So I get the eigenvalues to be 1,3,3 with 3 being the one with multiplicity of 2. For the eigenvector for 1 I get 1,-1,0 and for 3 I get 1,1,1 but here is the problem. For the other eigen vector for 3 the answer can be anything that satisfies x1=x2
x2=x1
x3=x3

so can something like 1,1,2 be the answer?

Sure it could. Try it out if you are unsure. There are a lot of choices for specifying the eigenvectors. Any linear combination of 1,1,1 and 1,1,2 will also be an eigenvector with eigenvalue 3.
 
  • #3
But wouldn't that mean there is no one definitive eigenbasis?
 
  • #4
xdrgnh said:
But wouldn't that mean there is no one definitive eigenbasis?

Sure it would. There never is. You have a two dimensional space of eigenvectors with eigenvalue 3. There are lots of ways to choose a basis. I wouldn't call any of them 'definitive'.
 

1. What is an eigenvector?

An eigenvector is a vector that when multiplied by a matrix, results in a scalar multiple of itself. In other words, the direction of the vector remains the same after the transformation.

2. What is a 2nd multiplicity eigenvalue?

A 2nd multiplicity eigenvalue is an eigenvalue that has a multiplicity of 2, meaning it has two eigenvectors associated with it. This is often seen in matrices with repeated eigenvalues.

3. Why is finding the eigenvectors of a 2nd multiplicity eigenvalue important?

Finding the eigenvectors of a 2nd multiplicity eigenvalue is important because it allows us to understand the behavior of a matrix and its transformations. It also helps in solving systems of differential equations and diagonalizing matrices.

4. How do you find the eigenvectors of a 2nd multiplicity eigenvalue?

To find the eigenvectors of a 2nd multiplicity eigenvalue, we first need to find the corresponding eigenvalue. Then, we can use this eigenvalue to solve for the eigenvectors by setting up and solving a system of equations.

5. Can a 2nd multiplicity eigenvalue have more than two eigenvectors?

Yes, a 2nd multiplicity eigenvalue can have more than two eigenvectors. The number of eigenvectors associated with an eigenvalue is equal to its multiplicity. So, if a 2nd multiplicity eigenvalue has a multiplicity of 3, it will have three eigenvectors associated with it.

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