Eigenvalue Question: Can I have an Infinite Matrix?

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Discussion Overview

The discussion revolves around the properties and characteristics of infinite matrices, particularly focusing on the existence of matrices with uncountable eigenvalues and the structure of matrices with a countable number of rows and uncountable columns. The scope includes theoretical aspects of linear operators and their properties.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions whether a matrix can have an uncountable number of eigenvalues if it is infinite.
  • Another participant suggests that instead of "infinite dimensional matrix," the term "linear operator" is more commonly used.
  • There is a follow-up inquiry regarding the possibility of a matrix having a countable number of rows and an uncountable number of columns.
  • A participant confirms that both questions posed are affirmative.
  • One participant expresses interest in other properties of infinite matrices.
  • Another participant mentions that a notable property of infinite matrices is that they do not need to be continuous, which they describe as a significant defect.
  • A participant proposes that a matrix with countably many rows and uncountably many columns could represent a linear map from functions to sequences.

Areas of Agreement / Disagreement

Participants generally agree that infinite matrices can exist with the properties discussed, but the conversation includes various interpretations and implications of these properties, indicating that multiple views remain on the topic.

Contextual Notes

Some assumptions about the definitions of matrices and linear operators may be implicit in the discussion, and the implications of discontinuity in linear maps are not fully explored.

cragar
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Can I have a matrix that has an uncountable number of eigenvalues?
If the matrix was infinite.
And also can I have a matrix with a countable number of rows and an uncountable number of
columns?
 
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Sure, you can have that. But we often don't speak of "infinite dimensional matrix" anymore, but rather of a linear operator.
 
Ok thanks for your answer. What about my second question?
Can I have a matrix with a countable number of rows and an uncountable number of
columns?
 
The yes was to both questions.
 
ok thanks. Are there any other crazy interesting properties of infinite matrices?
 
The craziest property, I think, is that infinite matrices don't need to be continuous. This is quite a serious defect, since discontinuous linear maps are not so interesting.
 
a matrix with countably many rows and uncountably many columns might be a linear map from functions to sequences.
 

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