Is the trace of a matrix preserved by an orthogonal transformation?

In summary, the transformation UMU^{-1} preserves the trace of a real, symmetric n by n matrix M, where U is the matrix of its eigenvectors as column vectors. This is true and can be easily proven using the cyclic property of trace. It does not require U to be unitary.
  • #1
ehrenfest
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Homework Statement


My statistical mechanics book says that if M is an real, symmetric n by n matrix, and U is the matrix of its eigenvectors as column vectors, then the transformation UMU^{-1} preserves the trace of M. Is that true? If so, is it obvious? If it is true but not obvious, how do you prove it?

Homework Equations


The Attempt at a Solution

 
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  • #2
It's true and obvious. And U doesn't need to be unitary. Use the cyclic property of trace. Tr(ABC)=Tr(CAB).
 
  • #3
Dick said:
Tr(ABC)=Tr(CAB).

Why is that true?

EDIT: never mind http://en.wikipedia.org/wiki/Trace_(linear_algebra )
 
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1. What is an orthogonal transformation?

An orthogonal transformation, also known as an orthogonal matrix, is a type of linear transformation in which the length and angle of vectors are preserved. This means that the transformation does not change the shape or size of the objects being transformed.

2. How is an orthogonal transformation different from other types of transformations?

An orthogonal transformation is different from other types of transformations, such as rotations and reflections, because it preserves both length and angle. This means that the transformed object will be an exact copy of the original, just in a different position or orientation.

3. What are some common applications of orthogonal transformations?

Orthogonal transformations are commonly used in computer graphics, particularly in 3D graphics, to rotate and scale objects without distorting the image. They are also used in signal processing, such as in Fourier transformations, to analyze and modify signals.

4. How do you perform an orthogonal transformation?

To perform an orthogonal transformation, you need to multiply the original vector or matrix by an orthogonal matrix. This can be done using various mathematical operations, such as matrix multiplication or rotation formulas.

5. Can an orthogonal transformation be undone?

Yes, an orthogonal transformation can be undone by multiplying the transformed vector or matrix by the inverse of the original orthogonal matrix. This will result in the original vector or matrix being restored to its original form.

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