# Questions tagged [terminology]

Questions of the kind "What's the name for a X that satisfies property Y?"

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### Why are isotropic random vectors called isotropic if they aren't?

A random vector $X \in \mathbb{R}^n$ is isotropic if $\mathbb{E}XX^T = I_n$. However isotropic random vectors don't have the property of isotropy. See 1. So why are they called isotropic? Similarly a ...
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### Trying to understand “moats”

According to the TSP Gallery moats provide lower bounds for the optimal solution of TSP instances. On the webpage they are depicted as blue rings around red disks, whose radii represent maximal vertex ...
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### What is a hull in the most general mathematical sense?

I have implemented an algorithm that filters the edges of simple complete graph with weighted edges according to a criterion that is inspired by elementary planar geometry and, to my surprise, in the ...
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### Probability Terminology

This is strictly a low-level terminology question. If I have a probability space $\Omega$ and a measurable space $S$, then a random variable $X:\Omega\rightarrow S$ gives rise via pushforward to a ...
190 views

### What is the name of this geometric structure, where we identify each sphere of vision with the sphere at infinity?

If you consider hyperbolic $n$-space $H^n$, modeled by the open unit ball $B^n \subset \mathbb{R}^n$, then given any two distinct points $x_1$, $x_2$ in $H^n$, there is a natural way of identifying ...
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### Dominant rational maps and compositions

According to many books (and also to Stack project, see https://stacks.math.columbia.edu/tag/01RI ), a morphism $f\colon X\to Y$ between schemes is said to be dominant if the image is dense in $Y$. ...
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### What is the name for a functor preserving open maps? Quotient maps? Effective epimorphisms?

How does one call an endofunctor of the category of topological spaces which preserves open maps? Quotient maps? More generally, how does one call a functor that preserves effective epimorphisms?
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### Infinite composition of continuous functions

Let $f_n:\mathbb{R}\rightarrow \mathbb{R}$ be a sequence of functions and define $F_n:= f_n\circ \dots\circ f_1$. Then $F_n$ is continuous. However, the pointwise limit need not be (consider Mateusz'...
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### How are these “Voronoi-dual” configurations called?

If $\mathscr P\subset \mathbb R^d$ is a discrete point configuration, take the Voronoi diagram of $\mathscr P$ and call $\mathscr P'$ the vertices of that diagram. I would like to know if ...
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### Name for a matrices having a specific property

is there an established name for the property that a square matrix can be made symmetric by permutation of its columns? Is it possible to recognize those kind of matrices efficiently?
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### Is there a name for order-preserving functions $f$ where “$a\le b$ if and only if $f(a) \le f(b)$”? [closed]

This is something only slightly stronger than monotonicity. I think that in category theory this would be a fully faithful functor, but I’m not sure if there is a standard name for this in order ...
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### Terminology: Existence + Representation

I'm looking to describe a result in a recent paper of mine, but I don't know if there is a term used for a result which is both an existence theorem and a representation theorem. Specifically, the ...
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### Why the name `Lipschitz-Free Banach spaces'?

There are many names for the same objects that is known as the Arens--Eells spaces, transportation cost spaces, free Banach spaces over a (pointed) metric space, and Lipschitz-free Banach spaces. The ...
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### Reference request for linear matrix inequality with PSD matrices

In literature, people say a spectrahedron is the following set $$\left\{x \in \mathbb{R}^d : x_1 A_1 + \cdots + x_d A_d \geq B \right\}$$ where $\geq$ is in the positive semidefinite sense. Is there a ...
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### Is there a name for and/or reasonably nice characterisation of “mixingly physical” measures?

Let $M$ be a Riemannian manifold with volume measure $\lambda$, let $f \colon M \to M$ be a diffeomorphism, and let $\mu$ be a probability measure on $M$ with compact support. As stated in the ...
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### What is a bipartite hypergraph?

Bipartite graphs are very useful, and I am looking for a generalization of this concept to hypergraphs. I found two different definitions of bipartite hypergraphs: In the Wikipedia page Hypergraph, a ...
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### Why aren't $B_n$ and $C_n$ the other way around?

In the classification of complex simple Lie algebras/groups, I have always been vaguely puzzled why $B_n$ and $C_n$ are labeled the way they are. I always instinctively want to put the special ...
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### Emergence of the orthogonal group

Do we know what mathematician first considered, and perhaps named, what we call the group $\mathrm O(n)$, or $\mathrm{SO}(n)$, for some $n>3$? I mean it specifically as group (not Lie algebra) ...