Proving Convexity of Numerical Range for Normal T

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SUMMARY

The discussion centers on proving the convexity of the numerical range for a normal linear transformation T in a finite-dimensional inner product space over complex numbers. Participants clarify that for T to be normal, it must satisfy the condition T*T = TT*, where T* is the adjoint of T. The main goal is to demonstrate that if a and b are in the numerical range of T, then the linear combination (1-c)a + cb is also within this range for 0 ≤ c ≤ 1, thereby establishing convexity.

PREREQUISITES
  • Understanding of linear transformations in finite-dimensional inner product spaces
  • Familiarity with the concept of normal operators in linear algebra
  • Knowledge of numerical ranges and their properties
  • Basic proficiency in complex numbers and their operations
NEXT STEPS
  • Study the properties of normal operators in linear algebra
  • Explore the definition and implications of numerical ranges in operator theory
  • Learn about the proof techniques for convexity in mathematical analysis
  • Investigate examples of linear transformations and their numerical ranges
USEFUL FOR

Mathematics students, particularly those studying linear algebra and operator theory, as well as researchers interested in the properties of normal operators and numerical ranges.

julydecember
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Homework Statement


If T is a linear transformation on the finite-dimensional inner product space over complex numbers and is normal, then prove that the numerical range of T is convex.


Homework Equations





The Attempt at a Solution


If we assume a and b are in the numerical range of T, then we have to prove that (1-c)a + c b is also in the numerical range of T for 0<= c <= 1. Can someone give some help, please?
 
Last edited:
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julydecember said:

Homework Statement


If T is a linear transformation on the finite-dimensional inner product space over complex numbers
which finite-dimensional inner product space? And what is the codomain of T?

julydecember said:
and is normal,
what does normal mean?

julydecember said:
then prove that the numerical range of T is convex.
Do you mean "prove that the image of T is convex"?
 

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