Commutivity of $A$ and $\sqrt{AA^*}$ in the proof of existence of compatible complex struture

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The following contents is in de Silva's Lectures on Symplectic geometry.

I can't understand the sentence of "Since $A$ commutes with $\sqrt{AA^*}$ "

Why these commute with each other?

Thank you in advance.

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It is because $A$ is skew-symmetric, $A^*=-A$. So $B$ also diagonalizes $A$ (but with imaginary eigenvalues).