# Unitary Transformation of complex matrix to diagonal matrix with positive diagonal elements

I 'm trying to prove that for any $$n \times n$$ complex matrix $$M$$ there exist unitary matrices $$A$$ and $$B$$ such that $$\Lambda=AMB$$, where $$\Lambda$$ is a diagonal matrix with positive elements. I have tried using schur lemma and try proving it for upper diagonal matrices but no luck.