# Tagged Questions

Use the convention tag for questions about standard, cultural practices in mathematics.

96 views

### The convention for speakers to refer to themselves at the board with a single initial

This question is being asked on behalf of a graduate student in my department. When and where did the tradition start of a seminar or colloquium speaker using just the first initial of the speaker's ...
144 views

### Which is the best notation for a sequence?

In a set, the order of its elements is (as far as I know) not important; in a sequence, the order of its elements is important. Which is the notation I should use in order to define a sequence? I ...
17 views

### Analogue of right-inverse for non-surjective function

Given a function $f: X \to Y$, not necessarily surjective, is there a common name (and more concise definition than follows) for a function which maps elements in $Y$ where $f$ is defined to elements ...
103 views

### Name and notation convention for “unnormalized probability”

Given a finite set of non-negative numbers $S={s_1,...,s_n}$, we can divide them by a normalization constant $Z$ (i.e. their sum) to get a probability distribution. Then we typically say (and write) ...
20 views

### what are the formal names of operands of unary operations?

In case of binary operations, operands have formal names. Taking addition for example: $$a + b$$ We can formally call $a$ the augend and $b$ the addend. Names for operands are available in individual ...
29 views

### A Summation Convention – Substitution Rule

I'm new to this forum. I'm starting a PhD – it's going to be a big long journey through the jungle that is CFD. I would like to arm myself with some tools before entering. The machete is Cartesian ...
33 views

### Value expressions

What is the value of the expression: $\sum_{k=0}^{d}b^{k}\left[\begin{array}{c} d\\ k \end{array}\right]\prod_{i=0}^{k-1}\left(c-b^{i}\right)$ for $k = 0$? In particular, what is then the value of:...
67 views

90 views

### Writing a Series of Equalities and Inequalities across Several Lines

What is the convention for writing a series of successive equalities and inequalities across multiple lines? Let me explain. Let $E_k$ denote an expression; for example, $E_0$ could be a sum or an ...
51 views

### Defining perpendicular lines in the 3D space

Is there a universal agreement about the definition of "perpendicularity" between two stright lines in the 3 dimensional euclidean space? Do they need to meet or it is enough to have perpendicular ...
46 views

### When talking about periods of a function why is it common to introduce a factor of $2$?

In many books I have read, when talking about periodic functions, they tend to write the period as $2\omega$. Why do we need the $2$? I haven't come across any working where the factor of $2$ is ...
48 views

15 views

### Symbol or name for Basismatrix of Linear Programming

This question is about the Basismatrix in the context of Linear Programming. Basically (haha!) we have the Matrix of the standard (or normal) form, which consists of (A|E) with the coefficient matrix ...
37 views

### problems on define set with polynomials

I'm trying to say set A is the set of nonnegative integers that not of this two forms $3x^2 + (6y-4)x - y\$ and $\ 3x^2 + (6y-2)x + (y - 1)$, for example: $4=3 \cdot1^2+(6 \cdot1-4) \cdot 1-1\$ is ...
58 views

### Graph diameter of a single vertex?

Convention-wise, given the simple graph with a single vertex, what is the graph diameter? I can see three options, zero, since there is a trivial path from the vertex to itself. infinity, since ...
42 views

### shouldn't we specify the topology when we talk about Borel $\sigma$-algebras?

Maybe this is me being pedantic, but this thought has just occurred to me. The Borel $\sigma$-algebra on X is the smallest $\sigma$-algebra containing all open sets. When we talk about Borel $\sigma$...
100 views

### decimal digit grouping delimiters

I feel a bit silly having to ask this but I just can't seem to find any resources that give an answer to this. When dealing with decimal values that have a large number of digits to the right of the ...
59 views

### Matrix with rank more than $1$

Is there a shorter way of saying that a matrix $A$ has rank more than $1$? I am looking for something like "full-rank", or "rank-deficient."