Completeness of eigenvectors of Hermitian Matrix.

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How do you show that eigenvectors of a Hermitian matrix form a complete set of basis?

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In the same way how you do that for normal matrices.

  1. Use or prove the Schur decomposition: for any square matrix $A\in\mathbb{C}^{n\times n}$, there is a unitary $Q$ and triangular $T$ such that $A=QTQ^*$. A simple but very strong result which can be shown quite simply by induction.

  2. Show that $A$ is Hermitian iff $T$ is Hermitian. A Hermitian triangular matrix is necessarily diagonal.

  3. The eigenvectors can be then found stuffed in the columns of $Q$.