Questions on the usage and meaning of words in mathematics, the names for mathematical entities, and other such questions.

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1answer
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Name for a collection of subsets of a set $E$ such that every element of $E$ is in some member?

Let $X$ be a set. A partition of $X$ is a collection of subsets $\{E_\alpha\}\subset\mathcal{P}(X)$ such that the following holds. For every $x\in X$, there is some $\alpha$ such that $x\in ...
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0answers
43 views

Vector calculus vs Vector analysis?

I was just wondering, is vector analysis the same as vector calculus? What about multivariable calculus? Because my multivariable calculus book (which I assume is the same as vector calculus?) covers ...
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1answer
34 views

Is there a name for the vector field that points along contour lines of a scalar field, proportional to the gradient?

Given a scalar field $G$ on $\mathbb{R}^2$ (say), the vector field $(\frac{\partial G}{\partial x}, \frac{\partial G}{\partial y})$ is called the gradient of $G$. Is there a standard name for the ...
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1answer
74 views

Terminological conventions regarding group actions

Suppose: $G$ is a group $T$ is a Lawvere theory ("algebraic theory") and $X$ is a $T$-algebra What conventions surround the phrase: "action of $G$ on $X$"? In particular, does this mean: a ...
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0answers
21 views

The basis induced by the nilpotent linear transformation

In Halmos's book, there is a theorem regarding the nilpotent transformation: If $A$ is a nilpotent linear transformation of index $q$ on a finite-dimensional vector space $V$, then there exist ...
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1answer
35 views

What does “421 is the smallest prime formed by the powers of two in logical order from right to left” mean and if so is it correct?

I've seen this on number gossip and a few other places, but I'm not exactly sure what it means. The only possibilities I have thought of for what they mean are "421 is the smallest center squared ...
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2answers
33 views

What is the name for one side of a ratio?

Basic example: "If you are asked to put a ratio in the simplest form, make sure that you have found the smallest factor that goes into both [?]." I've tried searching for ratio diagrams in Google, ...
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68 views

What is a nontrivial graph?

I've been operating happily under the definition that a nontrivial graph is a graph with at least two vertices for some time. Today I came upon a source which defined a nontrivial graph as a graph ...
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26 views

What to call a polynomial that with no roots in $\mathbb{Q}$ but does in $p$-adics

As an example, consider the polynomial $f(x)=x^2-2$. This polynomial has no roots over the rationals $\mathbb{Q}$. However, $\sqrt{2} \in \mathbb{Q}_7$, so it does have roots in the 7-adics. Is there ...
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1answer
32 views

Name for a nonlinear version of bilinear form

A map $b:X \times Y \to \mathbb{R}$ is called a bilinear form if $b$ is linear in both arguments. Is there a name for a form $b$ which is linear in only one argument and may be nonlinear in the ...
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0answers
40 views

What does it mean when two sets are “adjoined” in a metric space?

I encountered the word "adjoined" in Baby Rudin, Chapter 2 concerning basic topology on Euclidean space. It appeared in the proof to Theorem 2.35 Theorem$\quad$ Closed subsets of compact sets are ...
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17 views

What does it mean an ideal is nilpotent modulo another ideal?

Reference:Chatters, A. W.; Hajarnavis, C. R. (1971), "Non-commutative rings with primary decomposition", Quart. J. Math. Oxford Ser. (2) 22: 73–83, doi:10.1093/qmath/22.1.73 Let $R$ be an rng and ...
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1answer
24 views

Terminology help for a set relation: for sets $X, Y$, not necessarily disjoint, such that neither is a subset of the other.

Is there an existing term for pairs of sets $X, Y$, not necessarily disjoint, such that neither $X \subseteq Y$ nor $Y \subseteq X$? Would it be incorrect (or misleading) to call them something like ...
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1answer
21 views

Definition of quasi-cyclic and full rational groups

In Unit Groups of Classical Rings by Karpilovsky, p.96, we can see this theorem: Let $G$ be a divisible abelian group. Then $G$ is a direct product quasi-cyclic and full rational groups. I want ...
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1answer
43 views

Name when two functions are equal under integration (expectation)?

What is it called when $E[X] = E[Y]$? That is, $$\int x f(x)\,dx = \int y g(y)\,dy.$$ What I want to say is not that the expectation of $X$ is equal to that of $Y$ but rather (the equivalent ...
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2answers
135 views

What do we call the covector associated to a vector?

Let $V$ denote an inner product space. Write $V^*$ for either the algebraic dual, or else the continuous dual. In either case, for each vector $v \in V$, we get a covector $v^c \in V^*$ given by: ...
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0answers
113 views

When do the zero divisors of a commutative ring form an ideal?

Let $J$ denote the set of zero-divisors of a commutative ring $R$. Since we automatically have $RJ \subseteq J$, hence $J$ is automatically halfway to being an ideal. Furthermore, its already ...
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0answers
41 views

Proper names for different representations of the same formula

I would like to know what to call formulas that are all on one line and what to call the same formulas that are on multiple lines. One line example: P ÷ TVD ÷ 0.052 Multiple line example: ...
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1answer
29 views

Does “data” in Cauchy data come before or after the coinage of data in computer science

Is the usage of data as in Cauchy data (i.e. initial conditions) borrowed or came before the usage of data in computer science and do both usages mean roughly the same thing (data ~ information)?
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0answers
14 views

Is there a term for irreflexive relations whose reflexive closures are equivalence relations?

Consider a relation $\sim$ which is irreflexive, that is: $$ \forall A \:A\nsim A $$ Further suppose the reflexive closure of $\sim$ is an equivalence relation. The reflexive closure of $\sim$, ...
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1answer
50 views

prior probability vs a priori probability

What is the difference between "Prior probability" and "a priori probability" Wikipedia have two distinct pages for them. As of my inference i thought "Prior" and "a priori" are same, i.e., P(y) in ...
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0answers
25 views

By or through for a rotation

"Rotated through pi rad" vs "Rotated by pi rad" I have heard both used and also heard mentioned that there was a mathematical difference between the two. Is this true or can they be used ...
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5answers
417 views

Necessity of being Hausdorff in the definition of compactness?

According to R Engelking - General Topology: A topological space $X$ is called a compact space if $X$ is a Hausdorff space and every open cover of $X$ has a finite subcover, i.e., if for every ...
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0answers
31 views

Name (reference?) for lax monoidal functors that are 'full, or surjective, on monoids'?

A lax monoidal functor $F$ takes monoids to monoids. Is there a name for a lax monoidal functor that is 'full' or surjective with respect to this property? In other words, the functor $F : \mathcal{C} ...
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3answers
97 views

Is there any difference between 'all real numbers' and '$(-\infty, \infty)$'

I've just thought about this. All the textbooks I've been looking at for pre-calc, the domains are always written as 'all real numbers', whereas my calculus textbooks would rather write them as ...
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0answers
27 views

Name of a vertex set of the same out-degree

I have a graph and it is very important to me to distinguish vertex sets of the same out-degree. For example, I have a set of all vertex of the out-degree 1, a set of all vertex of out-degree2, and so ...
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1answer
18 views

Uniform closure of polynomials

What is the meaning of "uniform closure of polynomials"? I have seen it in Conway's Functional Analysis book VII § 5.
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1answer
20 views
1
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1answer
57 views

What does “thread” mean in general topology?

I am studying from "R Engelking - General Topology". In p.98 it is written: Why the word "thread" is chosen? I mean what's the relation to everyday meaning of thread?
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4answers
107 views

What is the direction along the edge of a circle called (in English and by chance German)?

Note: I am actually also searching for the term in German. That is why I posted this here (as opposed to the language SE's), besides me looking for this term in a mathematical/technical context. ...
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0answers
54 views

a new(?) operation using products of multiplicities

Does the operation $$n \odot m := \prod_{p \text{ prime}} p^{v_p(n) \cdot v_p(m)}$$ on positive integers have a common name? Has this operation been studied somewhere? Notice that $\odot$ is ...
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1answer
56 views

Graph theory - how to find nodes reachable from the given node under certain cost

I'm considering the following problem (very rough description): Assume we have a graph where edges are assigned some non-negative costs, a starting node s and some ...
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3answers
284 views

What is the name for a function whose codomain and domain are equal?

What do we call a function whose domain and co-domain are the same set? Edit: While i expressed my question in terms of functions, domains and codomains, i was actually interested in the most ...
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1answer
99 views

Should the empty set be called “half-open”? [closed]

Empty set is both open and closed in any metric space (also in any topological space). Consider $\mathbb{R}$ with usual metric. In this metric space, should we say that the empty set is half open?
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1answer
51 views

How to call a category with a single morphism between every two objects?

How to call a category where for every pair of objects $A, B$, there is a unique morphism $f\colon A\to B$? (A trivial category?)
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1answer
43 views

Why are free modules called “free”?

Let $R$ be a ring (not necessarily commutative) with multiplicative identity. A $R$-module $M$ is called free if $M$ has a linearly independent generating set $\beta\subseteq M$. That is, for any ...
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0answers
40 views

Confused about Graph Theory Language

I was confused about some of the wording in this definition I came upon: Let G be a control flow graph (a control flow graph you can imagine as a directed graph) for program P. A hammock H is an ...
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1answer
76 views

Is a function a derivative?

I'm reading introductory calculus and I find that 'function' tends to be defined by what it does rather than what it is. If $y = f(x)$, then surely the value of $y$ is dependent on that of $x$, i.e. ...
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0answers
49 views

What is a “note” (that might be published) in mathematics?

My background is not in mathematics but I am translating a novel from the French that has a few mathematicians as characters. A few times, the publication of a "note" is mentioned. This is the French ...
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1answer
31 views

Is there a concept called the cross derivative between two functions?

Let $f$ and $g$ be two real functions. Is there already a concept for the quantity $\lim_{h \to 0} \frac{f(x+h)-g(x)}{h}$? Note that when $g=f$, the quantity, if exists, is the derivative of $f$ at ...
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2answers
92 views

The phrase “up to”

I have begun seeing the phrase "up to" a lot after taking abstract algebra. I usually can figure out what means in context. For example, $\mathbb Z_4$ equals the set of rotations of a square, up to ...
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1answer
21 views

Jargon for maximum/minumum absolute value in a set

Given a group of numbers $-5,-3,1,2$, the maximum is 2, the minimum is -5. What is the mathematical jargon for the maximum and minimum in absolute terms (i.e. -5 and 1 respectively)? Basically, I ...
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3answers
104 views

G/N read as G modulo N.

In my abstract algebra course, the instructor is calling G/N (the set of left Cosets of N in G) G mod N. This has not yet been explained. Why is this the case? My immediate suspicion is some ...
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2answers
73 views

Name and role of a particular finite group?

The group generated by the functions $x\mapsto 1/x$ and $x\mapsto 1-x$ with composition of functions as the group operation is a non-abelian group with only six elements (listed below). Does this ...
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2answers
16 views

Correct term for percentage in decimal form

I have 35% of something, but when I calculate how much that is I multiply the total by 0.35 Is there a unambiguous word for the decimal form of a percent? "Decimal" is too broad because it can refer ...
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1answer
24 views

What's the name given to the ratio $P^2/A$ for a closed figure in the Euclidean plane?

Let $\mathscr{F}$ be the set of all plane, closed Euclidean figures having positive perimeter, and let $\sim$ be the similarity relation on $\mathscr{F}$. Then, for any equivalence class ...
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0answers
37 views

division algebras in Weil's Basic Number Theory

I have a question regarding the terminology in Weil's Basic Number Theory. In Corollary 5 of I-§4 (p. 14) there is a statement regarding division algebras over local fields. It starts like this: Let ...
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1answer
33 views

What is “Real coordinate space”?

What is the Real Coordinate Space in the discussion of vectors? How does it relate to Cartesian Coordinate System and Euclidean Space? P.S. Please, use naive terms.
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1answer
60 views

Name for a continuous surjection such that $\operatorname{cl}(f^{-1}(A)) = f^{-1}(A') \implies \operatorname{cl}(A) = A'$

Consider a continuous surjective map $f \colon (X, \tau) \to (X', \tau')$ satisfying $$\operatorname{cl}(f^{-1}(A)) = f^{-1}(A') \implies \operatorname{cl}(A) = A'$$ for all $A, A' \in \wp(X')$ I ...
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2answers
59 views

What is the general definition of a discriminant? (Not just the definition for polynomials)

For example, in regards to the second derivative test for a function of two variables, $D=f_{xx}f_{yy}-(f_{xy})^2$ is refered to as the "second derivative test discriminant." I know that D is the ...