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

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2
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0answers
33 views

Is there a name for functions $f$ such that $\{f \le a\}$ is analytic?

Let $X$ be a Polish space and $f : X \to \mathbb{R}$ an arbitrary function. In The limit inferior of Borel functions I showed that a certain function $f$ has the following property: For each $a ...
7
votes
2answers
252 views

Why the SVD is named so…

The SVD stands for Singular Value Decomposition. After decomposing a data matrix $\mathbf X$ using SVD, it results in three matrices, two matrices with the singular vectors $\mathbf U$ and $\mathbf ...
11
votes
7answers
9k views

What is the difference between an indefinite integral and an antiderivative?

I thought these were different words for the same thing, but it seems I am wrong. Help.
4
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1answer
51 views

What should you call a property, like an invariant, but that is reversed instead of preserved?

Suppose $P$ is some property of some objects and $f$ is a function on those objects. If $Px$ implies $Pf(x)$ and $\lnot Px$ implies $\lnot Pf(x)$, then we might say that "$P$ is invariant under $f$". ...
1
vote
0answers
53 views

Distribution of the kth powers of normal random variables.

If $X_1,..,X_n$ are standard normal random variables then it is known that: $\sum_\limits{i=1}^n X_i$ is a normal random variable and $\sum_\limits{i=1}^n X_i^2$ is a $\chi^2$-random variable. My ...
0
votes
3answers
45 views

What's logical symbol for “for some”?

"For every" $x\in S$ would be $\forall x\in S$ which it's same as "for all" $x\in S$. But, is "for some" is same as "there exist"? It seems Yes, but is it Yes for every time? In several texts I found ...
2
votes
2answers
59 views

Do “small” and “large” numbers actually exist in an absolute sense?

Numbers like $(10)^{-10^{10^{10}}}$ are generally regarded as small, whereas numbers like, for example, Graham's Number, are regarded as extremely large. My question is, are these numbers simply ...
1
vote
1answer
505 views

What is an isosurface?

I am trying to understand the marching cubes algorithm. I would like very much an easier definition of an isosurface than what is available online. Could anyone please explain it? Thanks.
3
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0answers
20 views

On a metric over m-subsets of [n]

Given an integer $n$, denote the set of integers $\{1,2,\dots,n\}$ as $[n]$. For two $m$-subsets $A$ and $B$ of $[n]$, list their elements in the increasing order as $a_1 < a_2 < \dots < a_m$ ...
4
votes
2answers
125 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: ...
11
votes
3answers
349 views

Has this algebraic structure been named or studied?

Apologies if this is is not very well-defined or exposes my ignorance; I know comparatively little about abstract algebra. The structure of certain programming languages can be described with the ...
10
votes
1answer
515 views

The word “integral” in calculus unrelated to “integral” / “integer” in algebra?

I think that the word integral in calculus is nothing to do with integer or integer numbers. But why is integral is chosen for integration? In algebra, integral means related to integers, and this is ...
1
vote
0answers
15 views

Directed Acyclic Graph - root and leaf node terminology

I have found conflicting terminology regarding how to label nodes in directed acyclic graphs. Specifically, I am looking for a definition of root and leaf nodes (preferably something to cite). For ...
2
votes
1answer
35 views

How to read $[G:N]$?

For a group $G$ and a normal subgroup $N$ of $G$, the quotient group of $N$ in $G$ is written $G/N$. I could find from this link how to read $G/N$ ("$G$ modulo $N$" or "$G$ mod $N$"), but I couldn't ...
3
votes
1answer
49 views

What is the precise difference between functions and operators?

I have heard affirmatively that all operators are functions, but not all functions are operators. But at the same time I have heard that functions map numbers to numbers, whereas operators map ...
4
votes
0answers
45 views

Terminology in graph theory

Let $G$ be a finite graph with the following property: For any vertex $a$ and edge $\{b, c\}$ of $G$, there is an edge connecting them: there is one of $\{a,b\}$ or $\{a, c\}$ in $G$. Is there ...
0
votes
0answers
48 views

Confusion regarding continuous functions between topological spaces – a subtle but possibly important point

Let $T: V_1 \to V_2$ be a linear mapping. Show that $T$ is a continuous function between $(V_1, \tau_{V_1}) $ and $(V_2, \tau_{V_2}) $ A direct solution to the problem is not what I am looking ...
1
vote
1answer
28 views

What do you call a graph where the vertices are signed?

Let $G = (V, E)$ be a graph, and $f: V \to \{1,-1\}$ be a function assigning a sign to each vertex. What is this system $(G, f)$ called? In my current research, we've been using "oriented graph" ...
0
votes
0answers
4 views

Successive divisibility of a sequence? Progressive divisibility? terminology or reference

Perhaps I say that an (infinite) sequence $(r_n)$ of positive integers is progressively divisible iff $r_n \mid r_{n+1}$ for all $n$. Is there some other terminology that is in use for this? I am ...
23
votes
2answers
5k views

Why are invertible matrices called 'non-singular'?

Where in the history of linear algebra did we pick up on referring to invertible matrices as 'non-singular'? In fact, since the null space of an invertible matrix has a single vector an ...
2
votes
2answers
131 views

Why is the exterior derivative called exterior derivative

I am studying exterior calculus, and I think I have some grasp of what is the exterior derivative. However its name still eludes me - why is it called a derivative? Is it just because the operator $d$ ...
4
votes
1answer
259 views

What is the difference between Calculus and Analysis? In Stochastic processes?

I guess one could say that Calculus is just a non-rigorous version of Analysis. What about in subjects involving stochastic processes? I took up masteral classes called stochastic calculus. I plan to ...
1
vote
1answer
13 views

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 ...
1
vote
0answers
34 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 ...
2
votes
1answer
33 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 ...
4
votes
1answer
39 views

Graph vertex set with a certain property

Let $G$ be a graph and let $V$ be a set of vertices with the following property: If a vertex $v$ is connected to every $u\in V$, then $v$ has to be in $V$. Does such $V$ have a (standard) name? Note ...
0
votes
0answers
19 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 ...
0
votes
1answer
66 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 ...
0
votes
1answer
77 views

What does it mean by “explode in finite time”? [closed]

I read some stochastic analysis book in probability theory (for the chapter of existence of solution) and it states "explode in finite time". What is the mathematical definition for this?
1
vote
1answer
90 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?
0
votes
1answer
34 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 ...
3
votes
2answers
32 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, ...
5
votes
2answers
695 views

what size is a “unit torus”?

Wikipedia articles on "unit sphere" and "unit circle" say the radius is 1. Articles on the "unit square" and "unit cube" say the length of the side is 1. Would you expect a unit torus to have major ...
0
votes
0answers
53 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 ...
0
votes
1answer
109 views

Why are some branches of mathematics called 'theory' and others not?

We say: graph theory , group theory, number theory , set theory, what is definition of theory? We also say abstract algebra, real analysis, but why we do not say abstract algebra theory or real ...
3
votes
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 ...
1
vote
0answers
24 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 ...
2
votes
0answers
35 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 ...
1
vote
1answer
17 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 ...
0
votes
1answer
70 views

What's the proper name for the evaluation function?

What do we call the (proper-class) function $$\mathrm{eval}(*,*)$$ such that for all functions $g$ and all $x \in \mathrm{dom} \;g$ we have $\mathrm{eval}(g,x) = g(x)$ ? I looked up 'evaluation ...
9
votes
1answer
6k views

What's the difference between early transcendentals and late transcendentals?

Anton, Bivens, and Davis have written calculus books with late transcendentals and Stewart has a calculus book with early transcendentals. What's this all about? edit 1: (Both terms show up in the ...
4
votes
0answers
112 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 ...
0
votes
0answers
16 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 ...
1
vote
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 ...
1
vote
1answer
22 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 ...
2
votes
0answers
36 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: ...
1
vote
1answer
44 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 ...
3
votes
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
13 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 $\sim$, ...
1
vote
1answer
42 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 ...