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

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SUMMARY

The trace of a real, symmetric n by n matrix M is preserved under the transformation UMU^{-1}, where U is the matrix of eigenvectors of M. This is established through the cyclic property of the trace, which states that Tr(ABC) = Tr(CAB). The transformation does not require U to be unitary, confirming that the trace remains invariant regardless of the orthogonal transformation applied.

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  • Understanding of linear algebra concepts, specifically matrix transformations.
  • Familiarity with the properties of the trace function in linear algebra.
  • Knowledge of symmetric matrices and their eigenvectors.
  • Basic understanding of orthogonal transformations and their implications.
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  • Study the cyclic property of trace in detail, including its applications in various matrix operations.
  • Explore the properties of symmetric matrices and their eigenvalues and eigenvectors.
  • Learn about orthogonal transformations and their significance in linear algebra.
  • Investigate the implications of trace preservation in different mathematical contexts, such as statistical mechanics.
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Students and professionals in mathematics, physics, and engineering who are studying linear algebra, particularly those focusing on matrix theory and transformations.

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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It's true and obvious. And U doesn't need to be unitary. Use the cyclic property of trace. Tr(ABC)=Tr(CAB).
 
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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