# Definition:Coordinate System

## Definition

Let $R$ be a ring with unity.

Let $\sequence {a_k}_{1 \mathop \le k \mathop \le n}$ be an ordered basis of a free $R$-module $G$.

Then $\sequence {a_k}_{1 \mathop \le k \mathop \le n}$ can be referred to as a coordinate system.

### Coordinate Function

Let $\left \langle {a_n} \right \rangle$ be a coordinate system of a unitary $R$-module $G$.

For each $x \in G$ let $x_1, x_2, \ldots, x_n$ be the coordinates of $x$ relative to $\left \langle {a_n} \right \rangle$.

Then for $i = 1, \ldots, n$ the mapping $f_i : G \to R$ defined by $f_i \left({x}\right) = x_i$ is called the $i$-th coordinate function on $G$ relative to $\left \langle {a_n} \right \rangle$.

### Coordinates on Affine Space

Let $\EE$ be an affine space of dimension $n$ over a field $k$.

Let $\RR = \tuple {p_0, e_1, \ldots, e_n}$ be an affine frame in $\EE$.

Let $p \in \EE$ be a point.

Since Affine Coordinates are Well-Defined, there exists a unique ordered tuple $\tuple {\lambda_1, \ldots, \lambda_n} \in k^n$ such that:

$\ds p = p_0 + \sum_{i \mathop = 1}^n \lambda_i e_i$

The numbers $\lambda_1, \ldots, \lambda_n$ are the coordinates of $p$ in the frame $\RR$.

### Coordinate

Let $\sequence {a_n}$ be a coordinate system of a unitary $R$-module $G$.

Let $\ds x \in G: x = \sum_{k \mathop = 1}^n \lambda_k a_k$.

The scalars $\lambda_1, \lambda_2, \ldots, \lambda_n$ can be referred to as the coordinates of $x$ relative to $\sequence {a_n}$.

### Origin

The origin of a coordinate system is the zero vector.

In the $x y$-plane, it is the point:

$O = \tuple {0, 0}$

and in general, in the Euclidean space $\R^n$:

$O = \underbrace {\tuple {0, 0, \ldots, 0} }_{\text{$n$coordinates} }$

Thus it is the point where the axes cross over each other.

## Also see

• Results about coordinate systems can be found here.