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βΊIn §22.19(ii) it is noted that Jacobian elliptic functions provide a natural basis of solutions for problems in Newtonian classical dynamics with quartic potentials in canonical form .
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βΊ
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βΊwhere is the (squared) angular momentum operator (14.30.12).
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βΊwith an infinite set of orthonormal eigenfunctions
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βΊis tridiagonalized in the complete non-orthogonal (with measure , ) basis of Laguerre functions:
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βΊFor either sign of , and chosen such that , , truncation of the basis to terms, with , the discrete eigenvectors are the orthonormal functions
…This equivalent quadrature relationship, see Heller et al. (1973), Yamani and Reinhardt (1975), allows extraction of scattering information from the finite dimensional functions of (18.39.53), provided that such information involves potentials, or projections onto functions, exactly expressed, or well approximated, in the finite basis of (18.39.44).
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βΊAssume that is an orthonormal basis of .
…where the limit has to be understood in the sense of convergence in the mean:
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βΊThe eigenfunctions form a complete orthogonal basis in , and we can take the basis as orthonormal:
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βΊEigenfunctions corresponding to the continuous spectrum are non- functions.
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βΊThe normalized system of products (31.15.8) forms an orthonormal basis in the Hilbert space .
For further details and for the expansions of analytic functions in this basis see Volkmer (1999).
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βΊThe sequence , forms an orthonormal basis in the space of -bandlimited functions, and, after normalization, an orthonormal basis in .
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βΊtaken over all subject to
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βΊFor the Laguerre polynomials this requires, omitting all strictly positive factors,
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βΊimplying that, for , the orthogonality of the with respect to the Laguerre weight function , .
…These results are proven in Everitt et al. (2004), via construction of a self-adjoint Sturm–Liouville operator which generates the polynomials, self-adjointness implying both orthogonality and completeness.
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βΊThe resulting EOP’s, , satisfy
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