vector space

Given a field F, a vector space over F is a set V with two operations defined on it:

• Addition of 2 vectors u,v in V: u+v;
• Multiplication of a vector v in V by a scalar c in F: c*v.

The operations are required to satisfy the following axioms. For vectors u,v∈V and scalars b,c∈F:

• Addition is commutative: u+v = v+u and associative: u+(v+w) = (u+v)+w.
• There exists a zero vector 0∈V such that for all v∈V, 0+v=v and for 0*v=0.
• Multiplication is associative: b*(c*v) = (b*c)*v.
• Multiplication is distributive across addition: c*(u+v) = c*u+c*v, and (b+c)*v = b*v+c*v.
• Multiplication preserves the field's unit: 1*v = v.

Examples

• If I is any set (called an index set) and F is a field, the set of functions I→F is a vector space over F:
  • Rⁿ is a vector space over the real numbers R (take I={1,2,...,n}).
  • Fⁿ is a vector space over F.
  • The set of all functions X→R is a vector space over R, for any set X.
• The set of functions from R to any vector space V over R is a vector space over R. (Of course this remains true if you replace "R" with any other field "F").
• The set of all continuous / differentiable / k times differentiable / analytic / almost any "nice" property functions X→Rⁿ, where X⊆R^m is some open set is a vector space over R.
• If F is a field and K⊆F is a subfield, then F is a vector space over K:
  • C (the complex plane) is a vector space of the real numbers R.
  • The finite field GF[p^k] is a vector space over GF[p].
  • R is a vector space over the rational numbers Q.

Many thanks to jrn and to scibtag for stubbornly insisting I have an error in the definitions -- the axioms (1*v=v) and (0+v=v) were missing!