資料來源 : pyDict
雙重的,雙的雙數
資料來源 : Webster's Revised Unabridged Dictionary (1913)
Dual \Du"al\, a. [L. dualis, fr. duo two. See {Two}.]
Expressing, or consisting of, the number two; belonging to
two; as, the dual number of nouns, etc., in Greek.
Here you have one half of our dual truth. --Tyndall.
資料來源 : WordNet®
dual
adj 1: consisting of or involving two parts or components usually
in pairs; "an egg with a double yolk"; "a double
(binary) star"; "double doors"; "dual controls for
pilot and copilot"; "duple (or double) time consists
of two (or a multiple of two) beats to a measure"
[syn: {double}, {duple}]
2: having more than one decidedly dissimilar aspects or
qualities; "a double (or dual) role for an actor"; "the
office of a clergyman is twofold; public preaching and
private influence"- R.W.Emerson; "every episode has its
double and treble meaning"-Frederick Harrison [syn: {double},
{twofold}, {treble}, {threefold}]
3: a grammatical number category referring to two items or
units as opposed to one item (singular) or more than two
items (plural); "ancient Greek had the dual form but it
has merged with the plural form in modern Greek"
資料來源 : Free On-Line Dictionary of Computing
dual
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)