I am trying the understand the spectral theorem as given in wikipedia link:
I understand that eigenvectors are vectors and unitary operator is a matrix. My question is: for a positive definite matrix $A=UDU^H$ is the set of eigenvectors $U$ is unitary? In the above equation $D$ is a diagonal matrix of eigenvalues. Can we form a general relation between set of eigenvectors of an operator to unitary operator?