资料来源 : pyDict

双重的,双的双数

资料来源 : 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.

资料来源 : 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"

资料来源 : 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)