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

84 votes
Accepted

How did "normal" come to mean "perpendicular"?

normalis already meant right-angled in classical Latin; for example, angulus normalis appears in the first century text De institutione oratoria (volume XI, paragraph 3.141) by Marcus Fabius Quintilia …
Carlo Beenakker's user avatar
55 votes

Who started the "-oid" suffix fashion in math?

The suffix "-oid" means the same as "quasi", so "resembling", "like". A groupoid is a quasi-group, like a group. There are hundreds of words in that category, covering many scientific disciplines. In …
Carlo Beenakker's user avatar
53 votes
Accepted

Whence “homomorphism” and “homomorphic”?

I found this footnote on page 195 of Fricke and Klein's Vorlesungen über die Theorie der automorphen Functionen (1897): Translation: The term "homomorphic" seems more appropriate than the previously …
Carlo Beenakker's user avatar
36 votes
Accepted

Cardioid-looking curve, does it have a name?

The name of the curve is cochleoid (= shell-shaped rather than cardioid = heart-shaped). I compare the two below (gold = cochleoid, blue = cardioid). The distinction shell/heart refers to the addition …
Carlo Beenakker's user avatar
28 votes

Naming in math: from red herrings to very long names

Let me address the question "what happens if some name it has already been used but you don't agree with the choice?", by giving a recent example from (mathematical) physics. The 2012 experiment that …
20 votes
Accepted

Why are free objects "free"?

Free objects were first defined* by MacLane in Duality for Groups. That paper gives "free" a curious political context, I quote from page 486: Call the dual (in this sense) of a free (nonabelian) …
Carlo Beenakker's user avatar
15 votes
Accepted

The $\zeta$-word

Well, Riemann himself says "I denote this function by $\zeta(s)$" ("Die Function [...] bezeichne ich durch $\zeta(s)$"), so I would think the choice of which letter to use for this function was his. …
Carlo Beenakker's user avatar
15 votes
Accepted

Whence "Durchschnitt" and "Vereinigung"?

An extensive discussion of the origin of "Menge" is given in Earliest Known Uses of Some of the Words of Mathematics (scroll down to "Set and Set Theory"). Cantor's (1880) Über unendliche linear Punkt …
Carlo Beenakker's user avatar
15 votes
Accepted

Is there a name for matrices of the form $a_{ij}=\frac{1}{a_{ji}}$?

The name of an $n\times n$ matrix with positive real elements satisfying $a_{ij}=1/a_{ji}$ for all $i,j\in\{1,2,\ldots n\}$ is reciprocal matrix. A consistent reciprocal matrix has elements of the for …
Carlo Beenakker's user avatar
13 votes

Emergence of the orthogonal group

There may be an earlier source, but Adolf Hurwitz 1897 is one upper bound: A. Hurwitz, Über die Erzeugung der Invarianten durch Integration, Nachr. Ges. Wiss. Göttingen (1897), 71–90. Hurwitz’s paper …
Carlo Beenakker's user avatar
13 votes

Where does the name "R-matrix" come from?

This answer refers to what is probably the first appearance of an $R$-matrix in the context of quantum mechanical scattering theory. Quite possibly the later appearances in the context of the inverse …
Carlo Beenakker's user avatar
12 votes
Accepted

What's the difference between a Riemann theta and a Siegel theta function?

It's the same function. I checked with Maple 15: $r := RiemannTheta([0.5+I, 2 I], Matrix(2, 2, [[I, 0], [0, I]]), [])$ $evalf(r)$ $-6.586149971*10^6-2.132900065*10^{-8} I$ Mathematica 8 gives $N[ …
Carlo Beenakker's user avatar
12 votes
Accepted

Why are Lagrangian submanifolds called Lagrangian?

This echos the 2017 comments, but since the question has now been bumped to the front page it might be helpful to give the actual source in Maslov's book [1]. [1] V.P. Maslov, Perturbation Theory …
Carlo Beenakker's user avatar
11 votes
Accepted

The ten martini problem - reason for name

The name was coined by Barry Simon in this 1982 article (page 487): The Ten Martini Problem: The almost Mathieu operator has a Cantor spectrum. The name comes from the fact that Mark Kac* has …
Carlo Beenakker's user avatar
9 votes

Is there a "mathematical" definition of "simplify"?

I guess you'll find much of what you would like to know in this 2004 paper by Jacques Carette (published here): We give the first formal definition of the concept of simplification for general …
Carlo Beenakker's user avatar

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