# [seqfan] Re: triple vs triplet

Richard J. Mathar mathar at mpia-hd.mpg.de
Sun Oct 25 21:54:33 CET 2015

```On behalf of http://list.seqfan.eu/pipermail/seqfan/2015-October/015489.html:

As far as I know (English being only my third language after German and Latin..)
a double, triple, ... is an ordered sequence of two, three ...
values, the n-tuple with n=2,3.... It also counts occurrences in statistics.

A triplet (quadruplet,...) is the physicist's name of
something that originates from a common source; the most common use of
that terminology is the Zeeman splitting of atomic lines in spectroscopy caused
by the magnetic term of the Hamiltonian (or its relativistic counterparts).

Music uses trios, quartets, quintets, etc for the number of musicians
needed to perform a piece in chamber music.

So the versions seem to differ mainly in saying nothing about association but
putting things into order on one hand, and looking at some sort of
binding/association on the other.

In geometry, an association of 3 is a triangle and something on a straight
line a 3-string (chain of 3, 3-on-line?). The OEIS uses frequently the word
triangle for matrices if values on one side of the diagonal are not used
or missing; so I guess the associated arrangement of 3 values on a line
then is a 3-vector (although "vector" is sometimes only used for rank-1
tensors?) if some linear algebra lies underneath.

Richard
```