# singularity

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## 1—10 of 87 matching pages

##### 1: 31.13 Asymptotic Approximations

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►For asymptotic approximations of the solutions of Heun’s equation (31.2.1) when two singularities are close together, see Lay and Slavyanov (1999).
►For asymptotic approximations of the solutions of confluent forms of Heun’s equation in the neighborhood of irregular singularities, see Komarov et al. (1976), Ronveaux (1995, Parts B,C,D,E), Bogush and Otchik (1997), Slavyanov and Veshev (1997), and Lay et al. (1998).

##### 2: 31.12 Confluent Forms of Heun’s Equation

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►Confluent forms of Heun’s differential equation (31.2.1) arise when two or more of the regular singularities merge to form an irregular singularity.
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►This has regular singularities at $z=0$ and $1$, and an irregular singularity of rank 1 at $z=\mathrm{\infty}$.
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►This has irregular singularities at $z=0$ and $\mathrm{\infty}$, each of rank $1$.
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►This has a regular singularity at $z=0$, and an irregular singularity at $\mathrm{\infty}$ of rank $2$.
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►This has one singularity, an irregular singularity of rank $3$ at $z=\mathrm{\infty}$.
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##### 3: 31.14 General Fuchsian Equation

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►The general second-order

*Fuchsian equation*with $N+1$ regular singularities at $z={a}_{j}$, $j=1,2,\mathrm{\dots},N$, and at $\mathrm{\infty}$, is given by ►
31.14.1
$$\frac{{d}^{2}w}{{dz}^{2}}+\left(\sum _{j=1}^{N}\frac{{\gamma}_{j}}{z-{a}_{j}}\right)\frac{dw}{dz}+\left(\sum _{j=1}^{N}\frac{{q}_{j}}{z-{a}_{j}}\right)w=0,$$
${\sum}_{j=1}^{N}{q}_{j}=0$.

►The exponents at the finite singularities
${a}_{j}$ are $\{0,1-{\gamma}_{j}\}$ and those at $\mathrm{\infty}$ are $\{\alpha ,\beta \}$, where
…The three sets of parameters comprise the *singularity parameters*${a}_{j}$, the*exponent parameters*$\alpha ,\beta ,{\gamma}_{j}$, and the $N-2$ free*accessory parameters*${q}_{j}$. … ►
31.14.3
$$w(z)=\left(\prod _{j=1}^{N}{(z-{a}_{j})}^{-{\gamma}_{j}/2}\right)W(z),$$

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##### 4: 31.1 Special Notation

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►Sometimes the parameters are suppressed.

##### 5: 16.21 Differential Equation

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►With the classification of §16.8(i), when $$ the only singularities of (16.21.1) are a regular singularity at $z=0$ and an irregular singularity at $z=\mathrm{\infty}$.
When $p=q$ the only singularities of (16.21.1) are regular singularities at $z=0$, ${(-1)}^{p-m-n}$, and $\mathrm{\infty}$.
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##### 6: 31.5 Solutions Analytic at Three Singularities: Heun Polynomials

###### §31.5 Solutions Analytic at Three Singularities: Heun Polynomials

… ►is a polynomial of degree $n$, and hence a solution of (31.2.1) that is analytic at all three finite singularities $0,1,a$. …##### 7: 36.14 Other Physical Applications

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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.
Diffraction catastrophes describe the (linear) wave amplitudes that smooth the geometrical caustic singularities and decorate them with interference patterns.
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##### 8: 1.10 Functions of a Complex Variable

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►Then $z={z}_{0}$ is an

*isolated singularity*of $f(z)$. …Lastly, if ${a}_{n}\ne 0$ for infinitely many negative $n$, then ${z}_{0}$ is an*isolated essential singularity*. … ► … ► … ► …##### 9: 12.16 Mathematical Applications

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►PCFs are used as basic approximating functions in the theory of contour integrals with a coalescing saddle point and an algebraic singularity, and in the theory of differential equations with two coalescing turning points; see §§2.4(vi) and 2.8(vi).
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