Solving systems of linear equations

Introduction

Introduction

\(m_{11}x+m_{12}y+m_{13}z=v_1\)

\(m_{21}x+m_{22}y+m_{23}z=v_2\)

\(m_{31}x+m_{32}y+m_{33}z=v_3\)

Matrix and vector notation

We can write the above as:

\(\mathbf{M}x=\mathbf{v}\)

What are the properties of \(\mathbf{M}\) and \(\mathbf{v}\)?

They are linear in addition and scalar multiplication.

Rank

Matrix rank

Rank function

The rank of a matrix is the dimension of the span of its component columns.

\(rank (M)=span(m_1,m_2,...,m_n)\)

Column and row span

The span of the rows is the same as the span of the columns.

Types of matrices

Empty matrix

A matrix where every element is \(0\). There is one for each dimension of matrix.

\(A=\begin{bmatrix}0& 0&...&0\\0 & 0&...&0\\...&...&...&...\\0&0&...&0\end{bmatrix}\)

Triangular matrix

A matrix where \(a_{ij}=0\) where \(i < j\) is upper triangular.

A matrix where \(a_{ij}=0\) where \(i > j\) is lower triangular.

A matrix which is either upper or lower triangular is a triangular matrix.

Symmetric matrices

All symmetric matrices are square.

The identity matrix is an example.

A matrix where \(a_{ij}=a_{ji}\) is symmetric.

Diagonal matrix

A matrix where \(a_ij=0\) where \(i\ne j\) is diagonal.

All diagonal matrices are symmetric.

The identity matrix is an example.

Other

Basis of an endomorphism

Changing the basis

For any two bases, there is a unique linear mapping from of the element vectors to the other.