Chapter 2: Dimensions of a matrix

The number of rows and columns in a matrix are written in the form rows×columns.

If you have a matrix like this   __    __     
                                            / 1 2 3 /
                                            / 4 5 6 /
                                            / 7 8 9 /

it has 3 rows and 3 columns, so the dimensions are 3×3. You read it aloud " three by three"
Matrices like that are called "square matrix"

Always remember: rows×columns       

 This is is a 1×3 matrix                            

This is a 3×3 matrix

This is a 3×2 matrix

This is also a 3×3 matrix (square matrix!)

The Identity Matrix

This is an example for an identity matrix.