Linear Algebra - Normal and Unitary Matrices

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Homework Help Overview

The discussion revolves around the properties of normal and unitary transformations in the context of linear algebra, specifically focusing on a transformation T defined on a unitary space V over the complex numbers. The original poster seeks to prove that T is a unitary transformation given certain conditions.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the implications of the condition T-1 = -T and its relation to the eigenvalues of T. Questions arise regarding the definitions and properties of the space V, including whether it is a general vector space or a specific type such as a Banach or Hilbert space.

Discussion Status

Some participants express confidence in the original poster's approach, while others seek clarification on the definitions used and the assumptions made about the space V. There is acknowledgment of the need for a clear understanding of the terms involved, particularly regarding the definition of a normed vector space.

Contextual Notes

Participants note that the term "general unitary space" may require further specification, and there is a discussion about the dimensionality of V, which is confirmed to be finite. The original poster also reflects on the clarity of their question formulation.

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Homework Statement


Suppose V is a unitary space [over C] and T: V -> V is a normal transformation that satisfies T-1=-T. Prove that T is unitary transformation.

Homework Equations


I know that T is unitary if and only if it is normal and the absolute value of its eigenvalues is 1. [*2]

The Attempt at a Solution


T-1=-T so T2=-I, now suppose a is an eigenvalue of T so T2v=a2v=-Iv what in turn means [itex]a=\pm 1[/itex].
So from [*2] we can conclude that T is unitary.

Have I missed something?
 
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Did you prove normality? Also, can you be more specific about V? Is it just a vector space? A Banach Space? Hilbert Space? Is it finite or infinite dimension? What definition of unitary are you using?
 
Thanks for posting!

Normality is given.
V is a general unitary space. [it means V is a general space over the complex field]
Forgot to mention: V is finite dimension space.
Unitary definition:[itex]T \cdot T^*=T^* \cdot T=I[/itex]
 
Ah yes, I see now that it was given. It looks fine to me, though I have to say I've never heard of a "general unitary space." Perhaps this is okay in this instance since [itex]\mathbb C[/itex] is algebraically self-dual, but normally one requires at the very least a normed vector space.
 
So I guess the prove is ok? [This question was formulated by myself so it is totally possible that I didn't define the question itself well]

What is normed vector space?
 
It looks fine so long as the result about being normal with modulus 1 is true. I think it's true, but haven't run through the proof myself. In any case, I would say you're good to go.

A normed vector space is a vector space with a norm. :) Not sure I can be more explicit than that.
 
Kreizhn said:
It looks fine so long as the result about being normal with modulus 1 is true. I think it's true, but haven't run through the proof myself. In any case, I would say you're good to go.

A normed vector space is a vector space with a norm. :) Not sure I can be more explicit than that.

Thanks!

Kreizhn said:
...
A normed vector space is a vector space with a norm. :) Not sure I can be more explicit than that.
I though every vector space has a norm, so I should not explicitly say it.
 

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