How to diagonalize NxNxNxN matrix

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Discussion Overview

The discussion revolves around the challenges of diagonalizing a symmetric NxNxNxN matrix, specifically in the context of finding eigenvalues and eigenvectors for a Hamiltonian. Participants explore the definitions and implications of higher-dimensional matrices and tensors.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant seeks methods to diagonalize a symmetric NxNxNxN matrix, noting its application to a Hamiltonian for determining energies and wavefunctions.
  • Another participant questions the definition of an "NxNxNxN" matrix, suggesting that a "4D matrix" is simply a 4x4 matrix and asks for clarification on the space it acts upon.
  • A participant clarifies that they meant an N by N by N by N matrix, indicating the use of four indices (ijkl).
  • Further inquiry is made regarding the multiplication of two NxNxNxN objects, suggesting a need for clarity on operations involving such matrices.
  • Another participant introduces the concept of tensors, explaining the hierarchy of tensor ranks and how they relate to matrices and higher-dimensional objects.

Areas of Agreement / Disagreement

Participants express differing views on the definition and implications of an NxNxNxN matrix, with some seeking clarification and others introducing related concepts such as tensors. The discussion remains unresolved regarding the methods for diagonalization and the nature of the matrix in question.

Contextual Notes

There are limitations in the discussion regarding the definitions of higher-dimensional matrices and the operations applicable to them, as well as the mathematical framework needed for diagonalization.

ann3
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I have a symmetric NxNxNxN matrix that I need to find eigenvalues a eigenvectors for. All the BLAS routines are for NxN matrices and I can't find anything that would work on a 4D matrix. Any tricks you guys know of?
If it helps to know, it's a Hamiltonian and I want to find energies and wavenfunctions.

Thanks.
 
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First of all, how are you going to define an "NxNxNxN" matrix? A "4D matrix" is just a 4x 4 matrix. On what space is such a matrix acting?
 
I misspoke, it's not a 4D matrix, it's an N by N by N by N matrix. So there are ijkl indices.
 
In what sense would you multiply two NxNxNxN objects?
 
I think you're talking about Tensors now. Rank 0 tensor = Scalar, rank 1 tensor = vector, rank 2 tensor = matrix, rank 3+ is where you get into stuff you can't really visualize.
 

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