Are eigenfunctions always normed and orthogonal?
131906
"An operator is hermitian". Implications?
54099
What are the eigenvalues of $\operatorname{ad}x$?
114208
Does non-symmetric positive definite matrix have positive eigenvalues?
155123
Selfadjoint Operator: Basic Criterion
1048
Discreteness of set of energy eigenvalues
141015
Proof of orthogonal matrix
78654
An example of a norm which can't be generated by an inner product
129549
Showing that the orthogonal projection in a Hilbert space is compact iff the subspace is finite dimensional
126337
Eigenvalues in orthogonal matrices
128361
The kernel and range of the powers of a self-adjoint operator
134981
Eigenvalues of $L^\dagger L$ are positive
14550
Every Hilbert space has an orthonomal basis - using Zorn's Lemma
45527
Do real matrices always have real eigenvalues?
5506
Perturbation property of Orthonormal basis for Hilbert space
59632
Bessel's function in spectral geometry
88153
Finding all inner products on $\mathbb{R}^2$ for which a given linear map is orthogonal
133711
Orthogonal basis for infinite-dimensional vector spaces