Eigenvalue of a rotation matrix

In summary, an eigenvalue of a rotation matrix is a scalar value that represents the amount and direction of scaling of the corresponding eigenvector when multiplied by the matrix. It is calculated by solving the characteristic equation det(A-λI) = 0, where A is the rotation matrix and λ is the eigenvalue. The significance of the eigenvalue lies in its ability to provide important information about the properties of the rotation matrix, such as stability and direction of rotation. A rotation matrix can have complex eigenvalues, which occur when it is a reflection or a combination of rotations and reflections. The eigenvalue is also related to the determinant of the matrix, as it is equal to the determinant and can be used to find the eigenvalues.
  • #1
supermesh
7
0
cos a -sin a

sin a cos a

How do I find the eigenvalue of this rotation matrix? I did the usual way, but didn't work! Could someone tell me how to start this problem?
 
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  • #2
How far did you get doing it the 'usual way'? It should work.
 
  • #3
Did you try solving the characteristic polynomial?
 
  • #4
A rotation matrix in C^n is unitary. Unitary linear operators have eigenvalues with absolute value 1 (because unitary transformations are also normal). You will get two complex eigenvalues, both with absolute value 1. Use the high school complex quadratic formula.
 
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1. What is an eigenvalue of a rotation matrix?

An eigenvalue of a rotation matrix is a scalar value that represents the amount and direction of the scaling of the corresponding eigenvector when multiplied by the rotation matrix. It is also known as the characteristic value.

2. How is the eigenvalue of a rotation matrix calculated?

The eigenvalue of a rotation matrix can be calculated by solving the characteristic equation det(A-λI) = 0, where A is the rotation matrix and λ is the eigenvalue. This equation is derived from the fact that when a vector is multiplied by a rotation matrix, the resulting vector is a scalar multiple of the original vector.

3. What is the significance of the eigenvalue of a rotation matrix?

The eigenvalue of a rotation matrix is significant because it provides important information about the properties of the rotation matrix. It can be used to determine the stability of a system, the direction of rotation, and the relationship between the eigenvalues and eigenvectors of the matrix.

4. Can a rotation matrix have complex eigenvalues?

Yes, a rotation matrix can have complex eigenvalues. This occurs when the rotation matrix is a reflection or a combination of rotations and reflections. In this case, the eigenvectors will also be complex.

5. How does the eigenvalue of a rotation matrix relate to the determinant of the matrix?

The eigenvalue of a rotation matrix is equal to the determinant of the matrix. This means that the determinant can be used to find the eigenvalues of a rotation matrix. Additionally, the product of all the eigenvalues of a rotation matrix is equal to the determinant, and the sum of the eigenvalues is equal to the trace of the matrix.

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