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Domain (mathematics)




In Mathematics , a domain of a ''k''-place Relation ''L'' ⊆ ''X''1 × … × ''X''''k'' is one of the sets ''X''''j'', 1 ≤ ''j'' ≤ ''k''.

If ''k'' = 2 and ''L'' ⊆ ''X''1 × ''X''2, then ''L'' is a Function defined as ''L'' : ''X''1 → ''X''2. It is then conventional to call ''X''1 the domain of the function ''L'' and to call ''X''2 the '''codomain''' of ''L''.


DOMAIN OF A FUNCTION

Given a of ''f''.

The .

A well defined function must map every element of its domain to an element of its codomain. For example, the function ''f'' defined by
: ''f''(''x'') = 1/''x''
has no value for ''f''(0).
Thus, the set of Real Number s, \mathbb{R}, cannot be its domain.
In cases like this, the function is either defined on \mathbb{R} \backslash \{0 \} or the "gap is plugged" by explicitly defining ''f''(0).
If we extend the definition of ''f'' to
: ''f''(''x'') = 1/''x'', for ''x'' ≠ 0
: ''f''(0) = 0,
then ''f'' is defined for all real numbers, and its domain is \mathbb{R}.

Any function can be restricted to a Subset of its domain.