The Eigenfunction reference article from the English Wikipedia on 24-Jul-2004
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Eigenfunction

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In mathematics, an eigenfunction f of a linear operator A on a function space is an eigenvector of the linear operator; it satisfies

for some scalar λ, the corresponding eigenvalue. The existence of eigenvectors is typically a great help in analysing A.

For example, is an eigenfunction for the differential operator

for any value of , with a corresponding eigenvalue .

Eigenfunctions play an important role in quantum mechanics, where the Schrödinger equation

has solutions of the form

where are eigenfunctions of the operator with eigenvalues . Due to the nature of the hamiltonian operator , its eigenfunctions are orthogonal functions. This is not necessarily the case for eigenfunctions of other operators (such as the example mentioned above)