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►Although divergent, these integrals may be interpreted in a generalized sense.
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►The fact that expansion (2.6.6) misses all the terms in the second series in (2.6.7) raises the question: what went wrong with our process of reaching (2.6.6)? In the following subsections, we use some elementary facts of distribution theory (§1.16) to study the proper use of divergentintegrals.
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►On inserting this identity into (2.6.54), we immediately encounter divergentintegrals of the form
…However, in the theory of generalized functions (distributions), there is a method, known as “regularization”, by which these integrals can be interpreted in a meaningful manner.
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►These are the structurally stable focal singularities (envelopes) of families of rays, on which the intensities of the geometrical (ray) theory diverge.
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►For divergent expansions the situation is even more difficult.
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►As an example consider
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►However, regardless whether we can bound the remainder, the accuracy achievable by direct numerical summation of a divergent asymptotic series is always limited.
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►From §8.19(i) the generalized exponential integral is given by
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►The transformations in §3.9 for summing slowly convergent series can also be very effective when applied to divergent asymptotic series.
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I. Shavitt and M. Karplus (1965)Gaussian-transform method for molecular integrals. I. Formulation for energy integrals.
J. Chem. Phys.43 (2), pp. 398–414.
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►The period is .
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►As from below the period diverges since are points of unstable equilibrium.
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►As from below the period diverges since is a point of unstable equlilibrium.
…As from above the period again diverges.
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►For large the corresponding asymptotic expansions (generally divergent) are used instead.
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►Stable recursive schemes for the computation of are described in Miller (1960) for and integer .
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