## Monday, October 3, 2011

### Math - Vectors - Vector spaces and some vector properties

According to Kaplan [1], a vector space, $$\left( v_1, \ldots, v_n \right) = V^{\; n}$$, contains the following properties:

\begin{align} \mathbf{I.} &= \mathbf{u} + \mathbf{v} = \mathbf{v} + \mathbf{u} \\

\mathbf{II.} &= \left( \mathbf{u} + \mathbf{v} \right) + \mathbf{w} = \mathbf{u} + \left( \mathbf{v} + \mathbf{w} \right) \\

\mathbf{III.} &= h \left( \mathbf{u} + \mathbf{v} \right) = h \mathbf{u} + h \mathbf{v} \\

\mathbf{IV.}&= \left( a + b \right) \mathbf{u} = a \mathbf{u} + b \mathbf{u} \\

\mathbf{V.} &= \left( a b \right) \mathbf{u} = a \left( b \mathbf{u} \right) \\

\mathbf{VI.} &= 1 \mathbf{u} = \mathbf{u} \\

\mathbf{VII.} &= 0 \mathbf{u} = \mathbf{0} \\

\mathbf{VIII.} &= \mathbf{u} \cdot \mathbf{v} = \mathbf{v} \cdot \mathbf{u} \\

\mathbf{IX.} &= \left( \mathbf{u} + \mathbf{v} \right) \cdot \mathbf{w} = \mathbf{u} \cdot \mathbf{w} + \mathbf{v} \cdot \mathbf{w} \\

\mathbf{X.} &= \left( a \mathbf{u} \right) \cdot \mathbf{v} = a \left( \mathbf{u} \cdot \mathbf{v} \right) \\

\mathbf{XI.} &= \mathbf{u} \cdot \mathbf{u} \ge 0 \\

\mathbf{XII.}  &= \mathbf{u} \cdot \mathbf{u} = 0 \; \; \text{if and only if} \; \; \mathbf{u} = 0 \end{align}

The first property in the above list is known as the commutative property or law which is true for vector addition [2]:

$\mathbf{A} + \mathbf{B} = \mathbf{B} + \mathbf{A}$

or with scalars [3]

$m \mathbf{u} = \mathbf{u}m$

Note:  I think there might be an error in Tai [4].  He states that the associative law is

$\mathbf{A} + \mathbf{B} = \mathbf{B} + \mathbf{A}$

or

$\mathbf{A} - \mathbf{B} = -\mathbf{B} + \mathbf{A}$

when I think he meant commutative.

The second property in the above list is known as the associative property or law which is also true for vector addition [2, 3]:

$\left( \mathbf{u} + \mathbf{v} \right) + \mathbf{w} = \mathbf{u} + \left( \mathbf{v} + \mathbf{w} \right)$

or with scalars [3]

$m \left( n \mathbf{u} \right) = \left (mn \right) \mathbf{u}m$

The third property in the above list is known as the distributive property or law which is also true for vector addition [3]:

$\left( m + n \right) \mathbf{u} = m \mathbf{u} + n \mathbf{u}$

or

$m \left( \mathbf{u} + \mathbf{v} \right) = m \mathbf{u} + m \mathbf{v}$

References: