Eigenfunction

In mathematics, an eigenfunction f of a linear operator A on a function space is an eigenvector of the linear operator; it satisfies
\mathcal A f = \lambda f for some scalar λ, the corresponding eigenvalue. The existence of eigenvectors is typically a great help in analysing A. For example, f_k(x) = e^{kx} is an eigenfunction for the differential operator \mathcal A = \frac{d^2}{dx^2} - \frac{d}{dx}, for any value of k, with a corresponding eigenvalue \lambda = k^2 - k. Eigenfunctions play an important role in quantum mechanics, where the Schrdinger equation
i \hbar \frac{\partial}{\partial t} \psi = \mathcal H \psi has solutions of the form
\psi(t) = \sum_k e^{-i E_k t/\hbar} \phi_k, where \phi_k are eigenfunctions of the operator \mathcal H with eigenvalues E_k. Due to the nature of the hamiltonian operator \mathcal H, its eigenfunctions are orthogonal functions. This is not necessarily the case for eigenfunctions of other operators (such as the example A mentioned above).

 

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