# isolated singularity

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## 1—10 of 87 matching pages

##### 1: 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*. … ► … ► … ►In any neighborhood of an isolated essential singularity, however small, an analytic function assumes every value in $\u2102$ with at most one exception. …##### 2: 32.2 Differential Equations

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►be a nonlinear second-order differential equation in which $F$ is a rational function of $w$ and $dw/dz$, and is

*locally analytic*in $z$, that is, analytic except for isolated singularities in $\u2102$. In general the singularities of the solutions are*movable*in the sense that their location depends on the constants of integration associated with the initial or boundary conditions. An equation is said to have the*Painlevé property*if all its solutions are free from*movable branch points*; the solutions may have movable poles or movable isolated essential singularities (§1.10(iii)), however. …##### 3: 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).

##### 4: 1.18 Linear Second Order Differential Operators and Eigenfunction Expansions

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►Often circumstances allow rather stronger statements, such as uniform convergence, or pointwise convergence at points where $f(x)$ is continuous, with convergence to $(f({x}_{0}-)+f({x}_{0}+))/2$ if ${x}_{0}$ is an isolated point of discontinuity.
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►Should $q(x)$ be bounded but

*random*, leading to*Anderson localization*, the spectrum could range from being*a dense point spectrum*to being*singular continuous*, see Simon (1995), Avron and Simon (1982); a good general reference being Cycon et al. (2008, Ch. 9 and 10). … … ►For this latter see Simon (1973), and Reinhardt (1982); wherein advantage is taken of the fact that although branch points are actual singularities of an analytic function, the location of the branch cuts are often at our disposal, as they are not singularities of the function, but simply arbitrary lines to keep a function single valued, and thus only singularities of a specific representation of that analytic function. … ►The materials developed here follow from the extensions of the Sturm–Liouville theory of second order ODEs as developed by Weyl, to include the*limit point and limit circle*singular cases. …##### 5: 1.4 Calculus of One Variable

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►A

*removable singularity*of $f(x)$ at $x=c$ occurs when $f(c+)=f(c-)$ but $f(c)$ is undefined. … … ►Ismail (2005, p 5) refers to these ${x}_{n}$ as isolated atoms. …##### 6: 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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##### 7: 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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##### 8: 31.1 Special Notation

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►Sometimes the parameters are suppressed.

##### 9: 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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