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I am trying to figure out whether the following implication is correct or not:

If $B$ is Hermitian and $A$ is Hermitian positive definite, then $A$ and $B$ commute.

Any ideas?

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    If it is a claim, then it shouldn't be a question...2012-04-20
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    Have you tried this for any pairs of matrices? Just make up some $2\times 2$ Hermitian matrix and some positive definite $2\times 2$ Hermitian matrix, and see whether they commute.2012-04-20
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    Try a couple examples with $A$ diagonal and $B$ non-diagonal.2012-04-20
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    And after you have tried some examples, if you then know what's up, you can post it as an answer.2012-04-20
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    Perhaps you mean "if $AB$ is Hermitian ..."2012-04-21

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By the following example, we can show that $A$ and $B$ don't necessarily commute:

Let $A=\begin{bmatrix} 1 & 0\\ 0 &2 \end{bmatrix} $

Let $ B=\begin{bmatrix} 1 &1+i \\ 1-i& 4 \end{bmatrix}$

$A$ is hermitian positive definite, and $B$ is hermitian. Note that: $$AB=\begin{bmatrix} 1 &1+i \\ 2-2i& 4 \end{bmatrix}\neq BA=\begin{bmatrix} 1 &2+2i \\ 1-i & 4 \end{bmatrix}$$