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Questions where the notion matrix has an important or crucial role (for the latter, note the tag matrix-theory for potential use). Matrices appear in various parts of mathematics, and this tag is typically combined with other tags to make the general subject clear, such as an appropriate top-level tag ra.rings-and-algebras, co.combinatorics, etc. and other tags that might be applicable. There are also several more specialized tags concerning matrices.

5 votes
2 answers
715 views

Matrices with same eigenvalues

It would for instance follow if we can write the matrices as $C_1 = AB$ and $C_2= BA$, but I don't see how such a decomposition could work. … In particular, this does not seem to be restricted to 5x5 matrices but holds for arbitrary matrices of the above form. …
António Borges Santos's user avatar
3 votes
1 answer
293 views

Eigenvalues two-fold degenerate

Consider the matrix $$A:=\left( \begin{array}{cccc} 0 & a & 0 & 0 \\ f & 0 & b & 0 \\ 0 & e & 0 & c \\ 0 & 0 & d & 0 \\ \end{array} \right)$$ I noticed that if I square this matrix then the eigenv …
António Borges Santos's user avatar
3 votes
2 answers
388 views

Monotonicity of matrix conjugation

Let $A$ and $B$ be positive-definite matrices such that $A \le B.$ By matrix monotonicity of the root, this also implies that $A^{\alpha} \le B^{\alpha}$ for $\alpha \in [0,1].$ I am now curious under …
António Borges Santos's user avatar
1 vote
1 answer
126 views

Matrix transformation that always works?

.$$ That there exists one such matrix for each set of coefficients is clear, since the eigenvalues of the two $3x3$ matrices are the same. I am looking for one that works for all choices. …
António Borges Santos's user avatar