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eigenvalues of matrices or operators

10 votes
Accepted

Eigenvalues of a matrix with entries involving combinatorics

Clearly, these statements 1 and 2 together imply that the eigenvalues are $1,l,\ldots, l^{n-1}$. We will assume throughout that $l\geq 2$, otherwise the statement is obvious. …
Lev Borisov's user avatar
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3 votes
Accepted

Proving 2 matrices have the same trace

Let's call $C=A-B$. Then you have $C^2=I_n$ and $BC-CB$ is invertible. You want to show that $C$ has an equal dimension of $1$ and $(-1)$ eigenspaces, which in turn implies both the equality $tr(A)=tr …
Lev Borisov's user avatar
  • 5,186
2 votes

When is this matrix singular?

For $\phi_j=0$ and $t_k=k$ you have (up to a constant) the matrix $A_{jk}= \lambda_j^k - \lambda_j^{-k}$ where $\lambda_j=\exp( i w_j)$. You can factor out $\lambda_j-\lambda_j^{-1}$ to get a matrix $ …
Lev Borisov's user avatar
  • 5,186