Questions tagged [singularity]

This tag is for questions relating to singularity, which is a point where a mathematical concept is not defined or well behaved, such as boundedness, differentiability, continuity. In general, because a function behaves in an anomalous manner at singular points, singularities must be treated separately when analyzing the function, or mathematical model, in which they appear.

A singularity or, singular point is a point at which a function, equation, surface, etc., becomes degenerate or just diverges towards infinity.

The word singular means something that is extraordinary, unique, and strange. When we talk about singularity in mathematics, we usually refer to the uniqueness of mathematical objects. In particular, singularities refer to the points where the mathematical objects are not well-behaved i.e. we can’t define them for those points.

Why we study about singularity:

The study of singularity is extremely important in many different fields. We employ complex mathematical formulations when we build physical structures and surfaces. These formulations are governed by the underlying functions, and if we don’t understand the singularities of those functions, the physical structure will collapse. Apart from this, they are used in particle physics, quantum mechanics, relativity, study of deformable surfaces, light patterns, and many more fields. We construct so many devices based on these physical phenomena, and all of them are critically dependent on their corresponding singularities

Singularity in Complex Analysis:

Singularities are extremely important in complex analysis, as they characterize the possible behaviors of analytic functions. Complex analysis refers to analysis of functions whose domain and range can include the complex number set. Complex singularities are basically points in the domain of a function where it fails to be analytic.

Classification:

Singularities can be non-isolated or isolated. Non-isolated singularities usually arise due to our own definitions of boundaries, like if we choose to define the function only within a certain limit. They are not very interesting to us because we know exactly why they occur. Isolated singularities, on the other hand, arise due the inherent nature of the functions. They refer to those isolated points where the function behavior is not defined. Isolated singularities may be classified as removable singularities, poles, essential singularities, and logarithmic singularities.

References:

https://en.wikipedia.org/wiki/Singularity_(mathematics)

http://mathworld.wolfram.com/Singularity.html

https://en.wikipedia.org/wiki/Singularity

1113 questions
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Finding poles, indicating their order and then computing their residues

I really don't understand the concept behind finding poles in Complex Analysis and I can't find anything on the internet or in books that helps me grasp the concept... The following are past exam questions that I'm looking at but don't know where to…
38
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Singularities, essential singularities, poles, simple poles

Could someone possible explain the differences between each of these; Singularities, essential singularities, poles, simple poles. I understand the concept and how to use them in order to work out the residue at each point, however, done fully…
smith
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Intuitive explanation of why some autonomous differential equations go to infinity in finite time

Take any differential equation of the form $$\frac{dy}{dx}=y^n$$ where $n > 1$. The solution $y(x)$ will reach infinity at a finite value of $x$. Assuming $y_0 =1 $ for all cases, here are a few examples: $$\frac{dy}{dx}=y^2$$ has the solution…
15
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2 answers

Asymptotics of $\displaystyle{\sum_{i=0}^n\sqrt{i(n-i)}}$ as $n\to+\infty$

I am studying a bit of asymptotics and for practice I decided to find the asymptotic of the following, $$s(n)=\sum_{i=0}^n\sqrt{i(n-i)}$$ as $n\to\infty$. This comes directly from this post, where @Gary provided some hints in the comments: $${\rm…
14
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Applications of resolution of singularities

I would like to know applications of Resolution of Singularities. What are the benefit of resolving singularities of a variety by blow-up maps in a context outside of mathematics? I'm fine with both positive and zero characteristics cases. The only…
12
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2 answers

Solve Poisson Equation Using FFT

I am trying to solve Poisson equation using FFT. The issue appears at wavenumber $k = 0$ when I want to get inverse Laplacian which means division by zero. We have ${\nabla ^2}\phi = f$ Taking FFT from both side we get: $-k^2\hat\phi = \hat f…
11
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1 answer

Understanding the singularity in $f^{-1}(x)=\int_0^x f(t)dt$

Note that here $f^{-1}(x)$ is the functional inverse of $f$. Clearly from the definition of the equation $f^{-1}(0)=0\Rightarrow f(0)=0$. By setting $x\to f(x)$ and differentiating one finds $$f'(x)f(f(x))=1$$ and therefore $\lim_{x\to…
10
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1 answer

Singular linear systems of ODEs

A classical problem in quantum mechanics involving the Dirac Delta function is given by $$ y''+(\delta(x)-\lambda^2)y=0. $$ Then, to find ''bound states'', you solve on the right and find the converging solution as $x\rightarrow \infty$, then solve…
9
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0 answers

Monodromy element: Why that name?

Let $(H,R)$ be a quasitriangular Hopf algebra, i.e. $R$ is a choice of an universal $R$-matrix for the Hopf algebra H. (You can find a definition of the term quasitriangular Hopf algebra on wikipedia.). One calls the element $Q:=R_{21}\cdot R_{12}…
9
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1 answer

A basic understanding of the Navier-Stokes, or Terry Tao's "exploding water" problem

The New York Times Magazine JULY 24, 2015 article The Singular Mind of Terry Tao starts off with: This April, as undergraduates strolled along the street outside his modest office on the campus of the University of California, Los Angeles, the…
8
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2 answers

How is the discriminant defined for $x^3+y^3+z^3+u^3+(ax+by+cz+du)^3+exyzu$?

Recently I am reading a book by Arnol'd et. al.. In this text I did not find the definition of discriminant $\Delta(a,b,c,d)$ : I wonder what is the meaning of the discriminant here ? The following is the discriminant of the cubic. I also found…
8
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2 answers

Prove $P(z)=z^4+2z^3+3z^2+z+2$ has exactly two zeros in the right half plane

NOTE: The answer found here is not what I'm looking for. The question is: Prove $P(z)=z^4+2z^3+3z^2+z+2$ has exactly two zeros in the right half plane. [Hint: Write $P(iy)=(y^2-2)(y^2-1)+iy(1-2y^2)$, and show that…
8
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1 answer

Blowing up the whitney umbrella over the z-axis

My professor gave us the example of the Whitney Umbrella as an example of a non-trivial resolution of singularities. I'm aware that to resolve the singularities of the Whitney Umbrella, I need to first, blow up the Whitney Umbrella over the…
Rushabh Mehta
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Is $z=0$ a pole of $1/\sqrt{z}$?

Consider the function $f:z\mapsto 1/\sqrt{z}$, defined, say on the right half-plane $Re(z)>0$. (We can resolve ambiguity by taking the branch that is positive for real $z$). Let $U$ be the right half-plane, and $a=0$. Then the following…
user167949
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8
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3 answers

Proving that the derivative always diverges faster than the original function

Let $f$ be a differentiable real function. What is the simplest/neatest way of proving that $\lim_{x \to a} f(x) = \infty$ implies that $ \lim_{x\to a} \frac{f'(x)}{f(x)} = \infty$? It seems like such a simple statement that perhaps there is even a…
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