Matrices Commuting with Matrix Exponential

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SUMMARY

The discussion centers on the relationship between matrices A and B, specifically whether the condition ##\left[ A, e^B \right]=0## implies ##[A,B]=0##. Participants explore counterexamples using nilpotent and skew-Hermitian matrices, emphasizing the complexity introduced by the properties of the exponential function. A key insight is that while ##[A,B]=0## guarantees ##\left[ A, e^B \right]=0##, the reverse is not universally true, particularly in cases involving skew-Hermitian matrices. The conversation highlights the need for specific conditions under which the implication holds.

PREREQUISITES
  • Understanding of matrix commutation and the notation ##[X,Y] = XY - YX##.
  • Familiarity with matrix exponentials, particularly ##e^B## for matrices B.
  • Knowledge of skew-Hermitian matrices and their properties, including unitarily diagonalizable characteristics.
  • Basic concepts of nilpotent matrices and their implications in linear algebra.
NEXT STEPS
  • Investigate the properties of nilpotent matrices and their role in counterexamples involving matrix commutation.
  • Learn about the implications of skew-Hermitian matrices in quantum mechanics and their relationship with unitary transformations.
  • Explore the conditions under which the exponential function is injective for matrices, particularly in the context of eigenvalues.
  • Study the implications of the Baker-Campbell-Hausdorff formula in relation to matrix exponentials and commutation.
USEFUL FOR

Mathematicians, physicists, and students of linear algebra interested in the properties of matrix commutation, particularly in the context of quantum mechanics and advanced matrix theory.

  • #31
Thanks.

StoneTemplePython said:
Looking at this in terms of a power series really misses the mark as we have powerful diagonalization theorems that we may lean on.
And if you want to kill the last "by-foot" step, you could substitute 4) by the adjoint representations and that exp is a local diffeo around 0.
 

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