There are four main components to a vector space:
- A set V
- A field F
- An operation “+” that allows us to add together elements of V
- An operation “⋅” that allows us to multiply, or scale, an element of V
Notation (V×W)
Given two sets V and W, we can make a new set V×W, which we would call the product of V and W, that is: V×W:={(v,w)∣v∈V,w∈W} or that V×W produces a new set of pairs of elements where the first element is all possible values of V and the same for the second and W.
Definition (Vector Space)
An F-vector space is a set V, together with an addition operation V×V(v,w)⟶V⟼v+w and a scalar multiplication operation F×V(c,v)⟶V⟼c⋅v (i.e. defined as (V,+,⋅)) that satisfy the following six rules:
- Commutativity: If v,w∈V then v+w=w+v
- Associativity: If u,v,w∈V and a,b∈F then (u+v)+w(ab)⋅v=u+(v+w)=a⋅(b⋅v)
- Additive identity: There is an element 0∈V such that for v∈V, 0+v=v
- Additive inverse: For every v∈V there is a w∈W such that v+w=0
- Multiplicative identity: For all v∈V, 1⋅v=v
- Distributivity: Given a,b∈F and v,w∈V, we have: a⋅(v+w)(a+b)⋅v=a⋅v+a⋅w=a⋅v+b⋅v
Notation (Set of Functions)
Let S be any set. We use the notation FS to denote the set of function from S to F.
Example: Sequences of real numbers: (ak)k=0∞, this describes a function f:N↦R where f(k)=ak. So (ak)k=0∞ can be considered an element of RN.
Notation (Polynomials)
A polynomial of one variable, with coefficients in F, is an expression of the form p(t)=antn+an−1tn−1+...+a1t+ao where ai∈F, ∀i=0,1,...n. The degree of p, denoted deg(p), is given by deg(p)=max{k∣ak=0} We use F[t] to denote the set of all polynomial with coefficients in F, and we use F[t]≤n to denoted the set of all polynomials with degree ≤n.