Triangular Similar Matrix question

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Discussion Overview

The discussion centers on whether every matrix is similar to a triangular matrix, exploring the implications and potential proofs related to this concept within linear algebra.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions if every matrix is similar to a triangular matrix and seeks a proof.
  • Another participant suggests that the proof can be approached by induction, mentioning that in the field of complex numbers, any n x n matrix has at least one eigenvector, which can be used to construct a basis for C^n.
  • This participant describes a method where the first column of the matrix can be made to have only the first element non-zero, leading to a block-triangular matrix, and proposes applying the inductive hypothesis to the remaining block.
  • Another participant states that every matrix is similar to a diagonal matrix or to a Jordan Normal Form, both of which are upper triangular.
  • A further contribution references the Schur triangle theorem, noting that matrices can be unitary similar.

Areas of Agreement / Disagreement

Participants present multiple viewpoints on the relationship between matrices and triangular forms, with no consensus reached on the proof or implications of the statements made.

Contextual Notes

The discussion includes various approaches to proving the similarity of matrices to triangular forms, but does not resolve the underlying assumptions or the completeness of the proposed proofs.

Alupsaiu
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Hi,

Is every matrix similar to a triangular matrix? If it is, anyone have an idea how to prove it?
Thanks
 
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Alupsaiu said:
Hi,

Is every matrix similar to a triangular matrix? If it is, anyone have an idea how to prove it?
Thanks

The proof can be done by induction. (Idea): In the field of complex numbers any n x n matrix has at least an eigenvector v. Complete v to get a basis of C^n. With respect to this basis, the first column of A has only the first element (let's call it a) eventually non zero, so A is similar to a block-triangular matrix, with a being the first 1 x 1 block and a certain (n-1)x(n-1) matrix B being the second block. Apply the inductive hypotesis to B and you get the result.
 
Every matrix is similar to a diagonal matrix or to a "Jordan Normal Form" both of which are upper triangular.
 
schur triangle theorem and it can be unitary similar
 

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