<mathematics> Every field of mathematics has a different
meaning of dual. Loosely, where there is some binary symmetry
of a theory, the image of what you look at normally under this
symmetry is referred to as the dual of your normal things.
In linear algebra for example, for any vector space V, over
a field, F, the vector space of linear maps from V to F is
known as the dual of V. It can be shown that if V is
finite-dimensional, V and its dual are isomorphic (though no
isomorphism between them is any more natural than any other).
There is a natural embedding of any vector space in the dual
of its dual:
V -> V'': v -> (V': w -> wv : F)
(x' is normally written as x with a horizontal bar above it).
I.e. v'' is the linear map, from V' to F, which maps any w to
the scalar obtained by applying w to v. In short, this
double-dual mapping simply exchanges the roles of function and
argument.
It is conventional, when talking about vectors in V, to refer
to the members of V' as covectors.
(1997-03-16)
Nearby terms:
D-type flip-flop « du « DUA « dual » DUAL-607 » dual-attached » dual boot
