Proof: Eigenvector of B Belonging to \lambda for A*S*x

In summary: So, in summary, the homework statement is trying to find an eigenvector of B corresponding to a specific eigenvalue, and the attempt at a solution shows that this can be done by multiplying by the eigenvector corresponding to the given eigenvalue. Next, the student is stuck on how to show that this corresponds to the desired result, but with the help of the previous information, they are able to conclude that A(Sx) = \lambda(Sx) and that this equation corresponds to the desired mathematical statement.
  • #1
WTFsandwich
7
0

Homework Statement


Let B = S^-1 * A * S and x be an eigenvector of B belonging to an eigenvalue [tex]\lambda[/tex]. Show S*x is an eigenvector of A belonging to [tex]\lambda[/tex].


Homework Equations





The Attempt at a Solution


The only place I can think of to start, is that B*x = [tex]\lambda[/tex]*x.
However, even starting with that, I can't figure out where to go next.
Could someone point me in the right direction?
 
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  • #2
WTFsandwich said:

Homework Statement


Let B = S^-1 * A * S and x be an eigenvector of B belonging to an eigenvalue [tex]\lambda[/tex]. Show S*x is an eigenvector of A belonging to [tex]\lambda[/tex].


Homework Equations





The Attempt at a Solution


The only place I can think of to start, is that B*x = [tex]\lambda[/tex]*x.
However, even starting with that, I can't figure out where to go next.
Could someone point me in the right direction?
That's a decent start. Next, show that A(Sx) = [itex]\lambda[/itex]x. That's what it means to say that Sx is an eigenvector of A corresponding to [itex]\lambda[/itex].
 
  • #3
What do I use to show that?

The only new information I've got that might be helpful is that A = S * B * S^-1

Multiplying on the left by S gives A*S = S*B

After doing that, I'm stuck again. I feel like this is the right track, but I don't know how to relate this back to what I'm trying to prove.
 
  • #4
Mark44 said:
That's a decent start. Next, show that A(Sx) = [itex]\lambda[/itex]x. That's what it means to say that Sx is an eigenvector of A corresponding to [itex]\lambda[/itex].
Slight correction: You want to show that A(Sx) = [itex]\lambda[/itex](Sx)
WTFsandwich said:
What do I use to show that?

The only new information I've got that might be helpful is that A = S * B * S^-1

Multiplying on the left by S gives A*S = S*B

After doing that, I'm stuck again. I feel like this is the right track, but I don't know how to relate this back to what I'm trying to prove.
Multiply by x now.
 
  • #5
I think I got it now.

After multiplying by x, I have ASx = SBx.

Bx has already been shown equal to [tex]\lambda[/tex]x, so I substitute that in, giving

ASx = S[tex]\lambda[/tex]x

[tex]\lambda[/tex] can be moved to the other side of S since it's a scalar, giving ASx = [tex]\lambda[/tex]Sx.
 
  • #6
Right.
 

Related to Proof: Eigenvector of B Belonging to \lambda for A*S*x

1. What is an eigenvector?

An eigenvector is a vector that, when multiplied by a square matrix, results in a scalar multiple of itself. In other words, the direction of the vector remains unchanged but its magnitude is scaled by a constant factor.

2. What is the significance of an eigenvector?

Eigenvectors are significant because they represent the directions along which a linear transformation has the simplest effect. They are used in many applications, including computer graphics, data analysis, and quantum mechanics.

3. What is the relationship between eigenvectors and eigenvalues?

Eigenvectors and eigenvalues are closely related. An eigenvalue is the scalar multiple by which an eigenvector is scaled when multiplied by a matrix. In other words, the eigenvalue represents the magnitude of the transformation along the corresponding eigenvector.

4. How are eigenvectors and eigenvalues calculated?

Eigenvectors and eigenvalues are calculated by finding the roots of the characteristic polynomial of a square matrix. This polynomial is obtained by subtracting the identity matrix multiplied by the eigenvalue from the original matrix, and then finding the determinant of this resulting matrix.

5. What is the practical application of understanding eigenvectors?

Understanding eigenvectors is important in many fields, including physics, engineering, and computer science. They are used in image and signal processing, data compression, and machine learning algorithms. In physics, eigenvectors play a crucial role in understanding quantum mechanics and the behavior of particles in a quantum system.

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