Determinat of a continous matrix?

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Discussion Overview

The discussion revolves around the calculation of the determinant of a continuous matrix, specifically in the context of a Hamiltonian in momentum representation. Participants explore the implications of having infinite-dimensional matrices and the challenges associated with finding determinants and eigenvectors in this framework.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how to calculate the determinant of a continuous matrix where the elements are defined as a function of real numbers.
  • Another participant notes that if the matrix elements are real, the matrix is symmetric, and suggests that an orthogonal matrix can be found to diagonalize the Hamiltonian matrix.
  • A formula for the determinant involving the trace and logarithm of the diagonalized matrix is proposed, but the participant expresses uncertainty about how to find the orthogonal matrix needed for this process.
  • There is a suggestion to search for a new basis made up of eigenvectors of the Hamiltonian to simplify the problem, although a challenge is raised regarding how to find these eigenvectors if only the matrix elements are known.

Areas of Agreement / Disagreement

Participants express multiple competing views on how to approach the problem, particularly regarding the methods for finding the orthogonal matrix and the eigenvectors. The discussion remains unresolved.

Contextual Notes

Participants highlight the complexity of working with infinite-dimensional matrices and the dependence on the specific definitions of matrix elements and eigenvectors. There are unresolved steps regarding the determination of eigenvectors from given matrix elements.

wenty
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Determinat of a "continous" matrix?

a(x,y) is a matrix element ,and x,y is the row and column index.
If x,y are real numbers, how to calculate the determinat of this matrix or the inverse matrix?

An example of this kind of matrix is <k|H|k'>,a Hamiltonian in momentum representation.
 
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So it's an infinite dimensional matrix...

If the matrix elements [itex]\hat{H}_{k,k'}=:\langle k|\hat{H}|k' \rangle[/itex] are real,then this matrix is symmetric.Then u can find an orthogonal matrix which would diagonalize the hamiltonian matrix.

Then

[tex]\det\left(\hat{H}_{k,k'}}\right)=exp \ \left(trace \ ln \hat{H}^{diag}_{k,k'}\right)[/tex]



Daniel.
 
dextercioby said:
So it's an infinite dimensional matrix...

If the matrix elements [itex]\hat{H}_{k,k'}=:\langle k|\hat{H}|k' \rangle[/itex] are real,then this matrix is symmetric.Then u can find an orthogonal matrix which would diagonalize the hamiltonian matrix.

Then

[tex]\det\left(\hat{H}_{k,k'}}\right)=exp \ \left(trace \ ln \hat{H}^{diag}_{k,k'}\right)[/tex]



Daniel.

The problem is how to find this orthogonal matrix.In ordinary case,to find this matrix we should solve an equation which needs to know the determinant of the given matrix.Then the question remains.
 
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How about u search for a basis (a new set of kets [itex]|k\rangle[/itex]) made up of eigen vectors (in general sense,the spectrum in continuous) of the Hamiltonian,and then everything would be tremendously simple...?

Daniel.
 
dextercioby said:
How about u search for a basis (a new set of kets [itex]|k\rangle[/itex]) made up of eigen vectors (in general sense,the spectrum in continuous) of the Hamiltonian,and then everything would be tremendously simple...?

Daniel.



But if what you only know is a(i,j),which isn's the matrix elements of the Hamiltonian,how do you find the eigen vectors?
 

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